My backhoe is using to combination pumps. This is my third replacement in less than 2 months.kindly assist me trouble shoot the possible cause on my combination piston pump. Using 1/2" horse combined as case drain. 1st failure of combination pumps Pump 1 · Low pressure of 900 psi · Wear on the valve plate Pump 2 · Retainer plate bend and wear on the pistons holes · Pistons shoes rounded, crashed and one piston separated from piston shoe · Swash plate had cut on the inlet half circumference · Slight wear on valve plate 2nd failure of combination pumps Pump 2 · Pistons rounded on shoes · Retainer plate cracked on kidneys and peeling on the drive shaft hole 3rd failure of combination pumps Pump 1 · Retainer plate crack on kidneys and wear on the pistons holes · Pistons shoes rounded, crashed and one piston separated from piston shoe · Swash plate/cradle had cut on the inlet half circumference · Wear on lower edge corner of the ball guide Pump 2 · Retainer plate wear on the pistons holes · Pistons shoes rounded · Swash plate/ cradle had slight pitting wear on the low pressure half circumference · Wear on lower edge corner of the ball guide
Did you flush the system?
I flashed for most of the pipes during the first replacement, but not the return to filter/tank main lines
Bearing in mind the lack of machine specific details, the two top causes of piston pump failure are, in my experience; Contamination Lack of flow to the pump inlet caused by, for example, a blocked suction screen or lack of tank head pressure.
This is rexroth A 10 VO 28 combination pumps. I managed the tank level well. The swash plates had cut on the low pressure half as shown on attached photos. Could that give a clue on the position of swash plate/craddle at the time of failure
When you have a pump failure putting that many contaminates in the hydraulic system a complete flush of the entire system is mandatory. Do have or have you read the installation manual. Did you follow the Rexroth installation instructions exactly as it is described in the manual ? Particularly about filling the pump with oil and bleeding the air out of the system before start-up ?
I filled the pump through case drain with oil. Then I connected the case drain connection to tank which is designed to be below the oil tank level. 1/2" horse pipe to tank is connected to case drain to both pumps? Or the case drain pipe too small to serve the two pumps?
Those are damaged parts on opening
Start around page #26 I thinks. https://md.boschrexroth.com/modules...AED1F692440.s142-vm&sch=M&id=14528,20,1208238
Is there any factory warranty on those pumps ? Are you using the factory recommended oil ? Other than new filters is there a screen in the hydraulic circuit that should be cleaned.
Looks to me like you have A cavitation problem as in supply or suction line restriction or high case drain pressure. Look for 1. Oil too thick or high viscosity 2. Restriction in supply line 3. Lack of tank pressure on pressurized system. 4. Blocked case drain or plugged case drain filter The case drain should be very little on a good pump and 1/2 inch line should do it . Just make sure there is nothing blocking it. Also make sure it’s not connected to the main return line causing back pressure. Also is there any motors on the same case drain line that are failing and causing high case pressure. Check the case drain pressure with a gauge while working it if you can .
This pumps are installed on venieri 12.23 backhoe. 1/2 case drain for two pumps is connected to an approximately 1" horse hydrolic pipe from hydrolic rediator and this return horse enters the the tank below fluid level. As for inlet condition, first failure may have been due to cavitation because of the gun like sound. 2rd failure and third doubt because no machine gun like noise.
Suction and case drain lines has no filters. Filter installed only on main line to the radiator which connects back to tank.
Lack of a filter on the pump case drain line and lack of a screen on the suction side screams "Cheap" to me, especially when using a piston pump. Dunno about anyone else. Why the fcuk didn't the manufacturer use a gear pump if they were going to skimp on filtration..? I think you are in for a complete system cleanout. I may miss something in the list below. If I do someone please shout out:- 1. Remove and clean hydraulic tank. 2. Remove and clean cooler 3. Remove, disassemble, and clean every hydraulic cylinder on the machine 4. Remove, disassemble, and clean every control valve on the machine. 5. Remove and clean every hydraulic hose & fitting. NOTE: Order a few cases of aerosol brake cleaner - you're going to need them. Just out of interest, what oil are you using in the hydraulic system..?
Pump 1 is connected to a priority valve which gives priority to steering wheel. Then any excess joins pump2 flow through a non return valve for work hydraulics. Pump 2 flow has a non return valve before joining excess pump 1 flow.
I am using shell tellus S2 m 46
That system has to be cleaner than a hospital operating room table when you get done doing everything Nige says. I would be looking closely at those non-return check valves.
Shouldn't be an issue with the oil provided it agrees with what the manufacturer recommends. What does the manual recommend..? However IMHO you could go to an ISO32 (equivalent to SAE10W) with no ill effects. That would satisfy all lingering doubts as to oil being "too thick". Otherwise refer to post #14 above. You may not like it, but you are in for a major amount of work.
Also to note, I think I am using close centre valves with compensator and load sensing dfr. Pump 1 which is connected to the priority valve had loop immediately at the output horse looped to its load sense port, I disconnected the loop because to me it was up stroking the pump unnecessarily if even when you required no flow. The steering valve has ls ports also the shovel valve and the backhoe valves.
What part of "completely clean every single piece of the system" is unclear to you..? The only factor that system complexity is going to affect is how long the cleaning process takes to accomplish to an acceptable level of cleanliness when completed. My bet is on at least a week, maybe two, even allowing for (super-clean) workshop facilities and tooling to be available. This is not a job that can be done anywhere. Once you've got it up and running my suggestion would be to sell it PDQ. Or alternatively if you have a large boat attach a chain to it and use it as an anchor.
How many hours did the machine have on it when the original pump failed ? If that loop that you removed was factory original you may have created a fatal flaw in the system. What I mean is, you may have two problems contributing to the failures now. Nige just now gave you the best piece of advice in this thread so far.
One has to ask what was wrong with the system (contamination in a valve somewhere maybe..? Hmmmm. now there's a novel thought.......) that was causing the undesired upstroking of the pump. The better way to fix it might have been to fix the underlying problem that was causing the undesired pump upstroke, not modify the system - My opinion (* other opinions may be available. YMMV)
I had a bit of a peruse of the Venieri web site. Your 12.23 model does not seem to be listed, the laergest backhoe is a 10.33. However one thing that struck me was the number of models that use a hydrostatic transmission. If that was the case on your particular machine it would explain the use of a piston pump. Does your machine have a hydrostatic transmission..? Is this what you have..?
I got the machine second hand from Italy. Maybe the first owner made the modifications. But let's look at the controls first if they are right. By tapping the output flow and feeding back to load sense unit for closed centre valves means the pressure increases to the compensator or relief valve setting whichever is lower. This changes the pump in my opinion to a fixed displacement pump.
For what little this is worth Nige.
I have never had issues with the transmission except when transmission fluid is low or in excess. The machine uses clerk automatic transmission. And suspect a branched shaft feeds the transmission pump.
Do you have a parts manual for it..?
I don't believe I've ever seen a closed center load sensing system that didn't have a suction screen in the hydraulic reservoir. The damage to the parts shown in the photos is typical for having a vacuum on the suction side of the pump. Slipper feet on the pistons only get damage like that when they are being pulled off the swash plate by vacuum and then slammed back onto the plate by pressure. My guess is that somewhere on the top of that tank is a bolted on plate with a stud in the middle that pushes down through a rod that connects to and holds a suction strainer in place over the outlet port of the tank. If there is no strainer, you had better figure a way to install one. Start there before you go any further.
I will clean the system before installation as advised. For the filter at suction, the filter is installed on the return line to tank but maybe the disigner assumed introduction of hydraulic oil from outside has to be absolutely clean. The inlet pipes are protruding some length above the tank flow.
If that's the case, the engineer isn't very bright. Without an inlet strainer, any failure will put chunkies right back into the pump. Major damage and rapid failure. At least the strainer will keep the big pieces from getting back into the system. It helps but small pieces cause a lot of damage. Ponder this: the smallest particle a human eye can see is 40 microns. The particles that cause major wear are under 5ish microns. They're the ones that are small enough to get in between spools and valve bodies. They cause the scoring and wear.
To clarify on control loop. I removed the bypass loop from outlet to load sense and reversed the non return valves on order to pump hydraulic fluid to a dead end. Then I set the idle pressure to 300 psi. Then I reconnected the loop which anabled me to build pressure to 3800 psi by adjusting the maximum pressure compensator and the main relief valve. Leaving main relief valve at 3800 psi, I adjusted the maximum compensator pressure to 3600 psi. I then removed the bypass loop and when the machine was at iddle, pressures never went beyond 300 psi. By either operating the steering, backhoe load valve, or shovel load valves the pressures goes beyond 1000 psi depending on load. To test the maximum pressure, I stalled the front bucket by lifting fully and the pressure did not exceed 3600 psi.
To clarify on control loop. I removed the bypass loop from outlet to load sense and reversed the non return valves on order to pump hydraulic fluid to a dead end. Then I set the idle pressure to 300 psi. Then I reconnected the loop which anabled me to build pressure to 3800 psi by adjusting the maximum pressure compensator and the main relief valve. Leaving main relief valve at 3800 psi, I adjusted the maximum compensator pressure to 3600 psi. I then removed the bypass loop and when the machine was at iddle, pressur
What does that have to do with the failed pumps?
To clarify on control loop. I removed the bypass loop from outlet to load sense and reversed the non return valves on order to pump hydraulic fluid to a dead end. Then I set the idle pressure to 300 psi. Then I reconnected the loop which anabled me to build pressure to 3800 psi by adjusting the maximum pressure compensator and the main relief valve. Leaving main relief valve at 3800 psi, I adjusted the maximum compensator pressure to 3600 psi. I removed the bypass loop and at iddle the pressures never went beyond 300 psi. By operating the steering, the front bucket or backhoe valves the pressures goes beyond 1000 psi depending on load. To test the maximum pressure I stalled the front bucket but never went beyond 3600 psi.
I explained it because someone had replied that by removing the bypass loop I may have changed the design and caused the pumps to fail.
Right on, John ! That is why I inquired as to why the loop was removed / altered. Geez "reversed the non-return valves" I was typing while you posted Eric. I posted earlier you may have created another problem with the loop removal. I see you know that prolly was contributing one of the contributing factors for failure. Like John C said you REALLY have to find a restriction in the suction side of the pump.
The non return valves were only reversed to enable setting the maximum pressures i.e pumping fluid to dead end. Thereafter they were put in right direction.
That's 300 psi on idle and maximum pressure 3600 at stalled conditions. Which are the required pressures in the system.
How about high case pressures. Can they have the same effect as high vacuum at inlet?
How about high case pressures. Can they have the same effect of piston and slipper separation as high vacuum at inlet?
Case drain can be designed into the system to ensure the pumps get oil. Most manufacturers use air pressure on the top of the reservoir to force oil into the pump. Some plumb an air compressor with a regulator, others use the up and down level of the fluid to suck air in and then hold it there. That might be something to look into. Do you have a breather/relief on the top of the tank that is plugged up. Most have a provision of a small air filter to ensure only clean air gets into the tank. Really high case drain pressures are a result of leakage in the pump caused by damage to the seal plate or the piston and barrel assemblies. I've seen some systems where a centrifugal pump is installed in the pump to ensure the case is always full. Your high case drain pressures basically happened after the pump was damaged.
I hope Nige, Tinkerer, John C and others don't lose your cool and leave this forum like what has happened in the past.
Thank you, mine seams gravity filled. will check the oil tank lid if it has breather
Having read what's gone on so far my vote for a first action would be - drain and remove the hydraulic tank from the machine. Open up all the inspection ports that it might have and get a good look inside it. Keep any particles you find. Then post photos of everything however insignificant it might seem. Like CSI, put something like a ruler beside particles when taking photos to give an idea of scale.
Okay will do that and get back, thank you very much
Did you ever reply to the question regarding if you have a Parts Manual for the machine..? If you do have one it might (depending on how good quality it is) be a key factor in helping identify things. Also it would be helpful to have a system operation document for the implement hydraulic system.
I could not get the workshop and repair manual for the machine. Please see attached
You are not trying hard enough to get the manuals. They are available , you have to be persistent in your quest for them. Any dealers that can look up what you need ? Where are you buying the pumps ? Unfortunately you cannot flush and clean the system without a working pump. Better order two of them.
The machine is quite old 1992 model. Is there a site you can recommend who might be selling these manuals? I bought replacement parts from panagon systems, USA. Will receive by next week.
(popcorn eating emote here)
You may have bought your pumps from PANAGON, but I think that's all you can get there. You have what I believe is a really obsolete, oddball machine in your part of the world. If you really are in Kenya the closest dealer to you is in Egypt. Good grief ! Your only hope for finding manuals is from a dealership. I used a VPN and located the company for you. https://www.vf-venieri.com/en/after-sales/
okay thank you. will make an inquiry
Correction. It’s an obsolete, oddball machine in ANY part of the world. I’ll be honest and say that even with 40+ years in the industry I’d never heard of the brand. That’s why getting hold of some good service documentation is a key factor in attempting to find and fix the root cause.
Your failure in my opinion was low charge pump pressure, the pistons and shoes are held on the swash plate by charge pressure and anytime you see failure of shoes and swash plates it indicate that there was not sufficient pressure to hold the shoes in contact with the swash plate. I do not know your operating habits but will say, Hydros were not made to be run at low RPM as any system I have worked on depended on RPM to maintain charge pressure. You must get that system cleaned up somehow as others have said, Hydros will tolerate no contamination. Also, if there is any leakage in the associated component that would also cause leakage of the charge pressure and any contamination from failed pumps is gonna go straight to components in its circuit.
Thank you all for your help. Had looked for the manual before but could not get. With your wealth of knowledge I think it possible to fix since we know every component in the machine. For example hydraulics pump is rexroth, priority valve is rexroth with steering priority for pump 1, steering pump is danfoss static non reactive with load sensing port, shovel control valve is rexroth closed centre with load sensing, backhoe control valve is rexroth closed centre with load sensing, brakes cylinder is safim hydraulic booster with engine driven hydraulic pump, transmission is clerk automatic 4 speed, engine is Perkins 4 cylinder 1004 turbo charged.
But it’s better to have a manual that tells you how the manufacturer intended things to work instead of trying to figure it all out from first principles.
It is better to have a manual but I've had occasion as well where it just wasn't going to be available such as this case. Sometimes you just have to do your best to recognize each component in the system and apply what you know toward how they likely work. I had forgotten about a charge pump possibly being installed in this machine. The thing is that a charge pump is usually used in a closed loop system and what is described here is an open loop closed center load sensing system with a priority steering pump that has the ability to also feed the implement functions. A close inspection of the piping between the hydraulic pump and the reservoir is in order. I don't recall now, did you find any tags on the pump or other components in the system? Sometimes you can do an on line search by any numbers on the tag that might provide more information and give you a clue as to how it is supposed to work.
Dis you read the Rexroth installation instructions, Eric ? Especially about new oil not being clean. Everything you need to know is in there. Including why you are having repeated failures. Notice that it says to not use the new pump to flush the system !
@Tinkerer just ordered cheaper pump parts from china to use for the flushing then later install more reliable parts
on the issue of filter on suction line here is screen shot from venieri 10.23C and no strainer on suction.
I suppose the best thing that can be said is that there is half-reasonable access into the tank to clean it out. Not having at least a suction screen in a system equipped with piston pumps is nothing short of criminal.
Items 2 and 3 are the types of covers I was talking about. Even the the parts drawing doesn't show any strainers, I would be pulling those covers if for no other reason than to clean out the tank. The drawing shows hoses 55 and 59 as being the same size as the pump discharge hoses. If you look at the actual hoses, is that true?
The persistence I mentioned earlier paid off for both of us, Eric. I also found and downloaded the parts book. I am posting a different page from the book that shows more of the circuit details. Is #47 in my image the valve(s) you reversed ? If not did you check it for an obstruction ? Have you flushed the cooler in the radiator ?
The parts book page posted by the OP looks interesting. I'd love to know the logic of how the oil flow into the fitler works when it's coming from two different places.
please note that this is not the actual machine manual, i was just using it to demonstrate luck of strainer at suctions of some venieri machines. @Tinkerer the page you referring to is transmission circuit. we are discussing hydraulic circuit. now that you have mentioned, there is a collection block for all return lines heading to filter and then tank e.g shovel valve, steering pump, backhoe valves. from manual on a similar venieri machine this block has check valves. i have never opened it and i think it might be full of wear debris. as earlier advised will remove the tank and inspect all openings.
Please tell me that the oil flowing in the transmission circuit and the oil flowing in the implement hydraulic circuit both pass through the same filter housing.......... That would just be the cherry on top of the cake.
Don't they share the same oil cooler ? That is why I posted the trans. circuit.
Oh deep ***kin joy........... now a transmission circuit to clean out as well. What's the transmission make..? Do we know..? It must be a bit of an oddball to run on ISO46 hydraulic oil in sub-tropical ambient temperatures. TO-4 oil maybe..? It wouldn't do the hydraulics any harm.
Exactly, Nige ! The cesspool gets deeper and deeper. It's going to take more money to fix it than its worth. IMHO !
Back to my suggestion of a couple of pages ago. Attach a length of large capacity chain to it and turn it into an anchor for a bulk carrier....... I wish to ***k that the Italians would stay out of the earthmoving equipment business.
The transmission and the hydraulic circuits are two different circuits. Each has different lines and filters. The main engine rediator has independent jackets at the sides for transmission cooling. The hydraulic system has a small hydraulic radiator in front of the main radiator.
That's the oil I use in the transmission
The attached is priority valve, steering orbitrol and shovel control valve I am using
So where is the tank for the transnmission oil..? Or are we looking at two separate tanks that just look the same, one on each illustration..? The transmission hydraulic circuit posted by Tinkerer above (post 64) appears to have at least one hose, maybe two, connected to the "hydraulic" tank.
Yes you are right, it seems for this model the transmission pump, hydraulic pump and brake pump are getting fluid from same tank. But mine has transmission dip stick on the right side and tank which is hard to notice. The hydraulic tank is on the left and very easily accessible.
OK, so we are back to common oil in both systems so that means the transmission system will also require a complete stripdown and cleanout. I'm not too impressed with your oil if it is being used in both a hydraulic system and also the powertrain. With my Cat background I'd personally look at an oil meeting TO-4 specification but maybe Tinkerer or John C might be able to suggest other suitable alternatives. It's going to be a real tightrope walking exercise to find an oil that meets the requirements of the transmission (friction modifiers for the clutches.?) and the demands of a hydraulic system that uses piston pumps. I see from one of your earlier posts that the transmission is a Clark and IMO that should work fine on a TO-4, probably a 10W which is more of an ISO32 than a 46. If you think that's light on viscosity I can tell you that most hydraulic systems in your type of climate generally run on 10W hydraulic oil. The only difference between a 10W hydraulic and a 10W TO-4 oil is the friction modifiers for the transmission clutch service, and I am of the opinion that said friction modifiers will affect the hydraulic system not one little bit.
You are misunderstanding me. The 10.23 c manual we are referring is not same us my backhoe design. My backhoe model is 12.23 and uses different dedicated lines for transmission and hydraulic fluid. I use S2ATF D2 automatic transmission oil for transmission and tellus 46 on the hydraulic system. I have no problems with the transmission at the moment but I have an issue with the hydraulic system.
Put some dye in one or the other and see where it goes. I would sure as he## be doing that before I would discount the possibility of cross contamination. I didn't misunderstand you Eric. But, you posted the first image from the wrong book. I thought when you did that it was pretty much same as your 12.23. I am wondering why you bothered posting a schematic of a system that doesn't have anything to do with the one we are trying to help you with.
There is a school of thought that says that suction screens cause too much restriction and they only get rid of the large particles not the stuff that causes the real damage. In my experience machines that have suction screens last a little longer than ones that don't.
It sure confused the ***k out of me ....... not difficult I hear you say.
Lets not forget that this machine was built years ago when maybe there wasn't a lot of refinement in high pressure load sensing hydraulic systems yet. In the probably time frame people were running automatic transmission fluid in high pressure hydraulics. Later on it became tractor hydraulic and then refined to the better stuff that we use today. I think there is a plan of action put together now so I hope Mr. Rop lets us know how the repairs turn out.
Sorry confusion
@Nige sorry for confusion, had explained earlier why I posted it.
The plan of action is: 1. I remove tank clean and inspect all openings. 2. Remove all lines and clean 3. Remove priority valve, shovel valve, backhoe valve, return block connector with its check valves, oil filter housing, cooler, engine driven pump, hydraulic master cylinder and all other components and clean. 4. All ascessible rams. 5. will flush the system using different pump parts from the ones I intend to finally use. 6. 4 rams which I am not able to access will force oil out of the return, then reverse and force oil from the opposite return since they are double acting. 7. Will then proceed to flush the system after removing and plugging load sense lines from the directional control valves. This create a continuous path from the pumps to the tank through the filter eliminating feedback to the pumps. Will then re-introduce the loops immediately from the pump outlet to load sense compensator to assist me upstroke the pump during flushing. This transforms the pumps from being variable displacement pumps to a sort of fixed displacement pumps. 8. Will set main relief valves to a much lower setting so that the pumps work at lower safer pressures during flushing. 9. Will also block the fluid from entering the cooler so that I work with much higher temperatures during flushing. 10. Finally will report back the results and then you can assist me on how we can modify the inlet and introduce filters.
How best do I introduce the inlet strainer to the machine. Are there safe distance to be considered from the pump inlet?
At the tank is good. Check out Stauff, they make that stuff.
You could also look at Hydac. Again they have a wide range. As an alternative to a suction screen what does the membership think regarding the installation of a high-pressure screen (or screens) after the pump(s) in an attempt to protect downstream components..?
The only company I know of using them in a heavy equipment application that has been successful is Komatsu. I bought some after market ones and put together a kit for Link-Belt loggers back in the nineties and what we found out is they have a specific life cycle on the steel castings. There was a phrase called the modulus of elasticity. That is what the engineers told me where the top of the case that the canister mounted in could only take so many pressure cycles before it changed shape and leaked or cracked and really leaked. The hard parts were good for between 3,500 and 5,000 hours and then you had to replace the whole filter housing. This being a smaller machine and likely running at a lower pressure, they might be good insurance. Space to mount them in though might be the real killer for using them.
John, HP screens are Standard fitment after the (piston) implement pumps on Cat large wheel loaders that have system pressures up to 5500psi and are hosed with XT-6 throughout. The only time they were ever taken apart was if a pump **** itself. No suction screens were fitted. I can’t ever remember one of those blowing its top. I’ll see if I can find a photo. Agree 100% regarding the space issue.
A machine I owned which had a transmission pump on a closed loop circuit, had a filter on the return line as well as a case drain. That machine suffered huge pressure spiking but never had any problems with the filters
I'm aware of the loaders. I should have said on excavators. In forty plus years I've only seen factory disaster catchers on Komatsu excavators.
When said disaster happens, how does the entire HP filter media not get solidly plugged with trash and rupture sending the trash down the line anyway?
if its "plugged" there is nothing left of the rotating group to load up
It's not a paper/cellulose/whatever filter element, it's a fine metal trash screen on a very stong support frame inside the housing. Basically as MB just said it plugs up more solid than a solid thing with debris from the pump that just **** itself. That debris literally has to be dug out of the screen housing with a shovel.
https://www.hydraulicspneumatics.co...2/the-truth-about-hydraulic-suction-strainers
The writer's opinion IMHO. And in my experience opinions are like a$$holes, everybody has their own ....... I'm not saying definitively that your system requires a suction strainer. I am however saying that IMHO it requires something more than what it has right now, because quite frankly what it was built with it ain't worth ****, again IMHO. (*other opinions are available - YMMV) Whether the "something more" turns out to be a suction strainer or an HP screen on the output side of the pump remains to be seen. Because right now you have a totally contaminated system that might have survived far better had its design been somewhat different.
I've run across that web site before and agree completely with Nige. Apparently all the major excavator manufacturers also agree with us. In any case you do need to remove the access plates and look inside for big and little pieces of pumps, cylinder packings and drive motor parts. The return filter will have plugged with the debris and the bypass would have opened letting that material travel into the reservoir.
Okay
The cooler in front of the radiator will need special attention. It has to be loaded with crap.
Finally opened tank it has wear debris as shown on attached photo
The outlet has no suction strainer just protruding outlet pipes as shown on attached outlet cover. The return line has no bypass relief on filter holder and no return check valves on return lines. Maybe the check valves are located at the control valves
Outlet cover
Well that mess just confirms what everyone was speculating and the fact that you have a long road ahead of you to decontaminate the system. Is aerosol brake cleaner available where you are.? If so I suggest that you invest in a couple of cases, just as a start. Please post some photos of the head assembly for the return line filter. Is the element a spin-on type or does it fit in a housing.? There is the possibility that the complete element assembly could lift off a "seat" to provide bypass relief but we don't know until we see photos.
I don't have the filter holder at the moment. But it's the housing type. I checked it very well it doesn't have any bypass hole between the inlet and outlet.
I have disconnected all the hydraulic lines and components for mechanical cleaning with the exception of the rams
Will check on serosal brake cleaner on Monday
Is there a big spring between the filter element and the housing on the “bottom” side..?
Yes spring at the bottom that pushes the centre hole with o ring in place
I mean pushes the filter against the center hole
I mean pushes the filter against the center hole
Keeeerching...........!! By the sounds of it that's the "bypass valve" - when the restriction to flow increases to a value that is more than the force generated by the spring, the whole filter element moves downwards and, guess what, unfiltered oil flows straight from the inlet to the outlet. Ifankyew.......
Okay, but when I checked the filter fins there were no as big debris as some in the tank. Is there possibility also as the shoes ceased the wear parts pass through the case drain to tank?
Did you cut the filter open anbd squeeze the media in a vice, then open up the pleats to check for particles n the base of them..? See this video, it's generic and for engine oil but it gives you enough of an idea how to do it. Doesn't matter what the system is, a filter cut works exactly the same way. Fast forward to about the 3-minute mark.
Absolutely, but don't let that fool you into believing that the rest of the system has somehow escaped becoming contaminated.
The tank inlet is shown on the attached photos with breather on the lid
Some of the shoe pieces will go to case drain , but when the shoe is failing the piston lube hole up the center of the piston will be at suction during the intake phase of it's rotation and the whole system will be contaminated. the system as many have stated must be disassembled and cleaned, It may have been mentioned but myself, I would install a couple strong magnets in the reservoir, it will not catch brass but will help with ferrous metal debris.
OK, so it is a combined tank cap and breather all in one. Probably has some sort of mesh inside the cap. I guess that the piece of square hollow section welded on to the bottom of the fill tube assembly must be designed to act as a type of baffle to prevent oil impacting directly on the underside of the filler cap/breather when the machine is moving and the oil is sloshing around in the tank. This also means that the tank breather is atmospheric and there is nothing to assist the oil flow from the tank to the pump inlet other than gravity and the suction from the pump itself. When the oil level in the tank is in the normal operating range, where is the pump inlet/suction port located (vertically-speaking) in relation to the oil level. Significantly below, a bit below, same level, or (God forbid) above the oil level..? I hope that you appreciate every hydraulic cylinder will have to come off the machine, and be disassembled and cleaned. If that is not done whatever else you are doing to the tank, valves, and lines, etc, is a complete waste of time.
Okay
Okay
After cleaning is to prevent re-occurence. As you have seen on my tank outlet manifold it may be difficult to install outlet strainer on the tank, how about installation on the suction lines?
Does the brake cleaner have any effect on the o-orings used in the control valves?
Not in my experience. If you are disassembling anything to clean it SOP would be to replace all O-Rings with new ones anyway. Before putting forward opinions about the potential location of a suction screen, the answer to the question "What is the height difference between the oil level in the tank and the pump suction port.?" needs to be answered. See post #121 above.
The cap should be like a radiator cap that will let air in and then hold it up to a set pressure. That air pressure is what forces oil into the pumps. If you pick up the loader boom through a couple of cycles first thing before putting the machine to work should charge the tank with enough air pressure. Nige has a very relevant question about whether or not the pump is mounted lower than the oil level in the tank. Most installations require the pump to be lower than the lowest normal level of oil in the tank. At this point a suction strainer appears to me to be something that would require welding some kind of bracket in the tank to hold the strainer in place and be a solid seal that would prevent debris from getting to the pump. Considering the base machine and the original design, it might not be worth the bother. Your question about mounting a strainer on the suction tubing is a good one. In my mind it would depend on how much room you have. The cylinders are a selective issue based on risk. How long did the machine run with a bad pump? Did the operator only stop when nothing would work, or did they just go until everything stopped? What attachments get used the most. In my experience some operations use the front loader more than the backhoe while others use the backhoe almost exclusively. Do you have drift in any of the cylinders? Answer each question and then weigh your risks of re-contaminating the system against the cost of repairing it all over again.
To confirm what type of breather it is, try blowing through either of the two holes circled in red (or even the four smaller holes immediately adjacent to them). Does the air come out of the holes close to the outer edge circled in blue..? If it does then you have an atmpspheric breather that is likely to be at best filled with some sort of metal mesh, probably similar to what your wife would use to scrub pans. Judging from the photo I'd also say that it will be full of a mixture of oily residue and dust.
From the photos there is hole on bracket below the tank inlet where you can hook up suction strainer glamp, problem is they are not vertically aligned to tank outlets
Ye Yes its oily paste was planning to clean. There are holes on the inside circumference, the seal and then holes on the outside circumference. Facing downwards may to avoid rain entry
Try blowing through the holes marked in red above as I suggested and report where the air exits. We need to determine if it holds pressure in any way or whether it is a purely atmospheric type of breather.
By blowing air on the red holes comes out from blue and vise versa
Atmospheric breather it is then, so no internal pressure generated in the tank by temperature, etc. That might be a reason to consider installing an HP screen after the pump and maybe even a filter in the pump case drain line back to the tank rather than a suction screen.
I opened and serviced shovel and backhoe control valves today but did not find metallic parts like the ones in filter and tank
Finished today mechanically cleaning all hydraulic components and rams. Tank inlet height to maximum hydraulic level is 220 mm, inlet pipe height to tank bottom is 120 mm, total tank height is 400 mm.
Sounds good, Eric. What is next in your repair sequence ?
What micron size filter is recommended for suction?
What's the difference in height between the "normal" oil level in the tank and whichever pump inlet port is the highest..? Until there is some information about the relative heights of the oil the the tank and the pump inlet port I'd say hold off on that. What you might consider as a first step (please not I'm not discounting the idea of a suction strainer yet) is installing a relatively-fine filter in the pump case drain line, even if that means doing something temporary and simply routing a return hose into where the tank cap would normally fit. 2-micron filtration of the pump case drain line might initially give you far more "bang for your buck" than a suction strainer IMHO.
Thank you very much for your assistance, I fear a filter on the case drain line, I prefer a suction filter. Will measure height from pump inlet to normal oil level in tank and get back to you
I think you would want a metal strainer more than a filter. You don't want any negative pressure on the suction line. I would suggest something to put a positive pressure in the tank if you do install a strainer of some kind. Maybe look into making sure that cap doesn't release the air pressure that naturally collects in the tank above the oil level.
Here’s the deal. You have an atmospheric (as opposed to pressurized) hydraulic tank. Anything that restricts oil flow in the suction side of the pump has the potential to induce oil starvation and possibly also pump cavitation. That’s why it’s important to know the level difference between the oil in the tank and the pump inlet port, because that height is the only thing the generates head pressure at the pump inlet. Whatever flow restriction might be put in that line will reduce said head pressure. I can’t think of a hydraulic system I’ve come across in an earthmoving machine equipped with a piston pump produced by a major manufacturer that didn’t have a case drain filter.
I agreed. Cat is the most common machine here. Kindly reccomend case drain filter for cat machine that may suit my modifications as per the following flow requirements and pressure. Maximum flow for the two pumps is 160 l/min. taking10% maximum allowable case drain flow, approximate maximum total case flow is 16 l/min. Maximum allowable case pressure for the pumps is 2 bars.
Agreed John, but the problem is that the cap vents direct to atmosphere so on the face of it pressure can't builld up in the tank at all unless the breather in the cap becomes blocked. See posts 128-132 on the previous page. The only thing I can think of is to replace the cap with something that seals tight and at the same time install a breaker/relief valve on the tank at another location. Then the tank could potentially generate around 10-15psi of internal pressure with the oil at operating temperature and there would be no negative aspects at all regarding the installion of a suction screen. I'll have a bit of a search for a suitable filter for the case drain bearing in mind the flow and the maximum stated pressure in the line. Eric, do you have the capability of getting hydraulic hoses manufactured somewhere close to where you are..? Obviously the installation of a case drain filter will require some new hoses as well. Space to mount the filter may also be an issue, but with no photos to go by it's a bit of a cr@p shoot. Probably right on the side of the hydraulic (if feasible) tank would be one potentially obvious location.
Horses of any size is non issue, space for case drain also is okay unless there is minimum length limitations. For suction, the minimum recommended suction pressures is 0.8 bar with a maximum of 5 bars.
Sorry the suction numbers don’t make any sense - unless of course they indicate that the pump manufacturer requires a positive pressure at the pump inlet...? Even if the specifications were absolute pressure (rather than differential pressure) on the face of it the pump manufacturer is looking for something pretty positive in the way of pressure at the pump inlet port. That would be an interesting scenario considering the fact that there is only atmospheric pressure in the tank. The only thing that can create any sort of pressure is the difference in head between the oil level in the tank and the pump.
Yes where I am located you would expect atmospheric pressure of around 0.8 bars. Our fluid column adds only 0.0245 bar above atmospheric. So total pressure in suction is 0.8245 bars, pressure drop across the biggest suction filter is how much?
That's interesting they give a positive pressure spec for pump inlet pressure, yet its only atmospheric pressure in the tank. Wonder if somebody put the wrong cap on the tank and that was the reason for the original failure?
Possibly, the equipment is not new from manufacturer and may be iterations of mistakes from first owner. Zero manuals from manufacturer meaning we have to put together what we know about every component in system, and basing on that information we try to understand how the machine was intended to work.
A radiator cap will fit nearly any hydraulic tank fill. The positive pressure given is ample evidence that the cap is suppose to let air in and hold to a set pressure. Five bar is 72.5 PSI. I'm sure a hydraulic tank cap could be found from some other machine that would fit.
Eric, can you post a photo of the top of the tank showing the cap removed so that people can see what the filler neck looks like..?
Possible, but let's not forget the machine was built in Italy. Anything could have happened, including the desoign engineer completely overlooking the need for a pressurized suction to the pump. Also the data regarding pressure at the pump inlet port (which remember we still haven't clarified is absolute or differential pressure yet) comes from the pump manufacturer, not the equipment manufacturer, unless I'm mistaken again. Eric, I know parts manuals are often not the greatest thing in the world for detail, but does the hydraulic tank cap you have installed right now in any way resemble what the parts manual shows..? Don't you agree that a radiator cap would not allow the tank to vent when cold.? I'm more accustomed to a sealed cap (often a screw-on) with a separate breaker/relief valve mounted somewhere on the top of the tank. Suffice it to say that either option would be better than what Eric has right now.
The radiator caps with the little dangly bit on the inside let air in if the pressure in the tank is less than atmospheric if that is what you mean by "vent when cold"
This is an image from the 10.23 model backhoe parts manual and may or may not be any help. I would think both models would use similar tanks and caps ??
I was wondering how far inside the frame the hydraulic tank was hidden. I'd found a few videos of the 12.23 but nothing appeared to show the hydraulic tank or even a filler cap that I could see. I guess the first question is how much pressure will the hose #13, the tubes/hoses #22 & 23, and the sight glass #25 be able to safely withstand.?
Find attached the photo of neck and filler cap
Mine does not have horse 22, 23 and pipe 11
That cap certainly matches the one in the image I posted. A pressurized tank would most likely require the wrench that is also in the image I posted. So, with the machine up to operating temperature the tank cap will be hard to remove without using the wrench. There should be puff a of air come out when the cap is removed. If not the cap is defective and not containing the required pressure for the pump suction. IMHO ! The Italian dummies should of had a threaded filler tube and cap in this situation.
Only the level gauge glass 25
It doesn't have 22, 23 and 11
That's good. it means all that concerns us regarding pressure is the sight glass. Is the tube made from some sort of plastic..?
The tank shape is like that but the suction manifold is bolted at bottom.
Eric is there any chance this information from the installation manual applies to your pump ?
Well from previous test Eric did the cap passes air freely in both directions, so the possible alternatives are - either the breaker-relief mechanism inside the cap has failed, or there was never a breake/relief mechanism on the first place. What do you think would be easier, trying to find a correct genuine replacement cap that would (hopefully) work correctly and generate pressure in the tank, or modify the existing filler neck to take an alternative cap that could be depended on to seal..? When I hark back to the arrangement of the filler posted earlier by Eric I woulkd personally lean towards cutting off the filler neck around where the ridge is on the tube and welding on a screwed adapter for a cap that would be guaranteed to seal. Eric, what is the approximate inside diameter of the filler tube..?
Filler pipe is around 2"
I need to do some checking but I think 7H-1447, the smaller of the two "standard" screw-on Cat hydraulic tank caps, is a 2" thread if my memory serves me correctly. It would still require a collar with the appropriate screw thread welded on the tank though. EDIT: I checked and the 7H-1447 cap is indeed a 2" one. The complete parts list is 1 of each. 7H-1447 Cap, 2D-4202 Plate, 6H-9361 Snap Ring, 8T-2275 Ball, & 9H-6454 Gasket.
That's where pump2 is connected to pump1. I only have an adapter
We can modify, I think it's the easier faster option
Are there any machine dismantling/scrap companies in your area..? Any old small/medium-size Cat machine should have a tank on it with a cap such as the one in the illustration. Hacksaw the neck off the tank at the same time (see photo) and you would have everything you need in one fell swoop. Alternatively source the cap first and then find a piece of threaded pipe to fit it.
Wh Yes we scrap yards for cat. Will look for the part. What pressure do expect after installing ?
Based on temperature I’d say it should develop something in the range of 5-10psi of positive pressure which IMO would be more than adequate.
I don't really any of the cat screw on caps having the vent capabilities.
They don't John, but the next step would be to install a breaker/relief valve in that flange on the top of the tank that carries the filler neck. I need to find one that will relieve somewhere between 5-10psi. Actually there are three to choose from. 507-0643 lifts @ 5psi, 188-8844 @ 7.5psi, & 507-0644 @ 10psi. All three will vent at around negative 0.1psi. I'd go for the 5 or 10psi personally. They are a more common Part Number. Priced around $100.
A parker 5 psi cap is available off the shelf. It should fit straight on.
Good spot. I wonder if it would be available in Kenya though..? Maybe I’m worrying about nothing but I wonder how well a twist-on cap will seal on to the existing tank filler neck.
I have got the attached, I think it can work
Looks like the ones shown on this document
I can also get this one.
Pump requirements
Well that answers the inlet pressure question - bars absolute. So the inlet port requirements expressed in differential pressure terms assuming normal 1 bar (sea level) atmospheric pressure are a range from 0.2bar (+/-80 inches of water) of suction to 4 bars (+/-60psi) of positive pressure. That puts a slightly different complexion on the inlet requirements, although FWIW I still am of the opinion that the pump would work far better with a positive pressure at the inlet port, even if it was only a couple of psi - and whatever additional pressure can be generated by the tank cap will also pay dividends in raising the maximum allowable case drain pressure (see below). Case drain pressure specifications are also interesting. It's probably going to need a fair size 2-micron filter to keep pressures within specifications.
Then the controlling pressure in tank is maximum allowable case drain pressure.
Is the 5 psi absolute or gauge pressure?
Most of the stuff I've worked with in hydraulics are done at gauge pressure. The absolute pressure given for the minimum feed is using absolute pressure to account for differences in elevation that the machine may be worked at. Most hydraulics systems for some reason like to have 14 PSI in the hydraulic reservoir. In your case, I would say any positive pressure is going to work better than what you had. As far as case drain filters go, many of the systems I've worked on in the past never had them. Basically, if that pump is making metal, that filter isn't going to prevent contamination of the system.
From this forum suggestions my main cause of 2nd and 3rd failures most likely have been contamination. The first in my opinion was cavitation because the pump was making gun like noises. This may have been due to someone draining tank oil to container with water. Also the fluid level in may not have been kept properly within limits.
Also the oil tank cork had dirt, I also experienced major horse failure necesitating change which may have introduced dirt in the system prior to first failure
I used machine for close to 8 months without major issues with hydraulics. There after failure happened approximately 2 weeks after repair
In a nut shale, I will modify the inlet as suggested, the Dayton filter I posted looks promising because has a strainer and pressure relief. Meaning introduction of dirt in tank is minimal. How about your opinions with this dayton breather?
On cleaning the tank today, the returning lines and the tank refill/inlet are on one end of tank where I found a hole drilled at the bottom and big chunks of pump wear material was trapped. The opposite end is the suction manifold.
Would like now to proceed with flushing the system. Kindly advise on that.
Also to note is oil main return line from filter goes to cooler thereafter before entering tank (approximately 2" metallic pipe) ;are provisions for case drain line. One port was plugged so introduced another case drain line meaning now each pump has its own case drain line connected to this 2" line in effort to reduce case drain pressure.
I would agree that the 2nd & 3rd failures could have most likely been caused by system contamination remaining from the 1st failure. However IMHO what you should not lose sight of is that you have a tank cap that apparently should generate (a small amount of) pressure in the tank to aid pump suction. That cap was not functioning as designed if you could blow through it in both directions. That failing should be addressed at the same time you are decontaminating the system. Piston pumps don't suck too well. They like a postive flow of oil into them under pressure, either from the oil level in the tank being significantly above pump suction port height (not possible in your case) or by a system that generates pressure in the hydraulic oil tank. Out of those two options only one appears to be available to you.
Totally agree with Nige. The pump height has a lot to do with this kind of failure. A machine I owned had the load sense piston pump mounted above the tank oil level, it **** it self twice. To fix that problem I put a radiator cap on the tank and ran I hose from the engine inlet manifold to the tank with a pressure reducing valve so now the turbo charges the tank. Oh and that machine was Made in America (with pride) apparently. The idiot company who made it still dose the same crap.
Similar case - Cat 994 wheel loader (all models). The implement pumps (four of them) suction ports are probably a couple of feet above the oil level in the tank. The breaker relief valve in the tank is set to relieve at 35psi. 'Nuff said.....
You did not have any issue on case drain after raising the tank pressure?
There hasn't been any issues at all. The hose to the tank is set at 7psi, the cap is 10psi. The turbo can make 25 psi at W.O.T
The radiator cap let's air in at lower pressure?
No, the air goes in below the cap. I can get a pic of it next week, bout Wed.
Since all the breathers I am getting I am not sure if the hold pressure. Will modify with radiator cap since I am sure about the hold pressure. A cap rated 0.9 or 1.1 means absolute or gauge pressure?
Gauge pressure.
Finished the modifications
Finished flashing system and getting 15 psi absolute at the tank
Drilled port F thats where I am getting 15 psi s I am getting 15 psi
Those extra images can be edited out if you want Eric. Unless the time limit has expired for editing. Is the gauge visible to the machine operator ? In one of my service manuals it clearly states --- Do not operate hydraulics until 15 psi. is reached in reservoir. But, it is pressurized from the air brake system.
N It was a temporary installation to check on the pressure, will consider a permanent installation for the operator.
Well that should solve the problem of pump suction (or lack of it). Now you can install a suction line screen with confidence - but just remember now that you have 15psi in the tank the screen will have to be reasonably robust because if it ever plugs significantly the tank pressure could turn it inside out. Only the contamination issue to resolve now, and you have the light at the end of the tunnel.
What's the expected pressure drop across the suction filter?
I'd prefer to call it a screen and it all depends if it's plugged or not. If it's not plugged, pressure drop across it will be negligible. If it is 100% plugged with fine material assume as a worst case scenario that the pressure drop across it is 15psi (tank pressure).
What about fitting a gauge between the screen and pump, placed so the operator can see it as well as the gauge before the screen? This would allow the operator to see when there's a significant pressure difference and hopefully clean/change the screen when it needs it.
Thank you Nige and team for your assistance. I just reopened the pumps for inspection after operating for a week and it was in a good condition. Only might be running a little hot at the engine part. The engine is Perkins turbo charged 1004-4T and temperature gauge shows maximum of 100 degrees c. Is this normal operating temperature for this engine?
That's pump outlet horse pipe fitted with an orifice. What's the function of orifice on pump outlet?
Are you 100% sure that the hose in the photo is both genuine and original..? If yes, my bet is that it's an engineering "bodge" by the equipment manufacturer's engineers to get the pump to do something that the pump manufacturer did not design it to do. My opinion, others may differ.
I've seen orifices like that in load sense lines. I wouldn't think that line is an output but would have to see the schematic again to be sure. Where does the hose go to?
Looks like not genuine because it is only 1 foot and installed at the centre of main pipe
The load sense compensator requires a pressure differential between pump outlet and load sense compensator to function properly. But isn't this orifice provided in load sense control valves?
Does paragraph 1 mean the directional valve itself is an orifice and there maybe no need for installation of another orifice?
In all the variable displacement systems I've worked on there are a few control pressures used as references. Springs in the regulators are the first controls and set the base level of control. Pump outlet pressure, many times internally sensed from internal porting but also may be crudely connected just by an external pipe or hose back to a fitting on the regulator is a second control type. That plus spring pressure is the basis for pump control. The next one or two depend on if the system is open center load sensing or closed center load sensing. Open center load sensing uses two hoses and an orifice plus a regulator in the main control valve while a closed center system uses a single hose from the main control valve that gets its pressure from some kind of manifold that connects all the function outputs. Your system might even be pressure compensated control with no load sensing. Basically the operating pressure in the system acts on the pump regulators and backs off flow as the pressure rises in the system. Where on the pump does the hose with the small orifice connect? Where on the control valve does it connect? It is very possible that it is the wrong hose completely. It would be fun to figure out your system with my hands on it but unfortunately my hands and arms can't reach you from here.
My pump has both compensator and load sense control with closed centre directional valves with ls circuits. What you see on the picture is an orifice on the main pump outlet that feeds the directional valve and it seems out of place.
If that is an outlet, then I would definitely be getting it replaced with the correct size hose and fittings. That would certainly cause heat problems.
It is beginning to look like there is more than one piece to the puzzle of his pump failures. Is it possible that the hose was mistakenly switched with the correct one while all those pump replacements were being done ?
Not while I was doing the pump replacements most likely the previous owner was struggling with this machine and trying things out. There are two things which I think we're not right in the pump: 1. Pump no. 1 had 1/4 inch horse pipe connected immediately after leaving the the pump at its output and the load sense valve 2. Now pump no. 2 as discovered has an orifice at the pump output.
You got that right - see below ...... So all of a sudden 12 pages into the thread and it comes out that you bought the machine with problems that the previous owner struggled with, and failed to resolve. Didn't you think that this information was pertinent to mention before..?
These issues were discovered 1 at time for example the latest where the orifice is on the discharge pipe
What I’m getting at is that rather than the pump problems having developed during your ownership of the machine, you bought it with problems that a previous owner had tried and failed to rectify. That is very pertinent information that might have helped everyone to help you better had you seen fit to mention it before before.