What are some of the tricks to get all of the air out of hydraulic cylinders and lines, especially when starting with new components? This is something I've struggled with my entire working life, it seem like whenever I have something completely apart or I'm installing a new cylinder I have a dickens of a time getting the air out. I've tried everything from pre-filling the cylinder with a tiny funnel then holding that fitting end up while pushing the cylinder in to squeeze any air to the top. I've tried hooking up the lines and leaving the highest fitting loose while forcing fluid though the circut, then tighten it mid stream (like you would bleeding brakes). I've tried doing both of the above then cycling it many times with the cylinder at various angles. Often nothing seems to completely work, sometimes I just live with it, but others like my current project are downright dangerous with air in the lines. Right now I've working on a tractor mounted hydraulic post driver, put new tilt cylinders on (they require .031" restricted orifice fittings to move slow enough) and with any amount of air in those circuits they move very fast and erratic. What am I missing, I don't think I'm that bad of a mechanic?
I've always just cycled the cylinders gradually, extending the amount of travel a little bit further each time until I'm running it full stroke. Can't recall ever having issues with air.
It sounds like you're doing everything reasonable to purge air which is something I, myself have been burned by in the past. Dipper cylinders are the ones I'm fighting the most. Slow, deliberate exercise at idle, never reaching end of travel till after many many cycles is what most mfrs recommend. I've found that the higher viscosity oils tend to not detonate as easily. Now , I use 56 or higher in whatever I can get away with. Good luck.
Have not really run in to a situation where air couldn't be worked/purged out of the system except on nexgen 374's and 395's which have a lengthy procedure of pressurizing the hyd tank and then pulling a vacuum on a hand full of test ports
I will try the slow and gradual method of cycling the cylinders. I had just been running them stop to stop but it sounds like that may be wrong.
I would agree with what @funwithfuel wrote above. I think it is standard practice in Cat manuals to 1) rebuild cylinders with the piston at mid-stroke, and 2) excercise the cylinder a small distance in each direction from the centre at engine idle speed, gradually increasing the distance of movement and observing how smoothly it moves back & forth before finally moving the cylinder to full stroke in both directions. Taken from - "A Procedure for Initial Cycling of Hydraulic Cylinders to Remove Air and Prevent Cylinder Dieseling" Use the following procedure when air has been introduced into the cylinder: All cycling is to be done at low engine idle. Cylinders should be cycled with the rod unpinned from the linkage. Ensure that the oil level is at or above the full mark on the sight glass on the hydraulic tank before performing the cylinder cycling process. Always orient cylinders in the horizontal position or parallel to the ground where possible. Cylinders that are exercised vertically do not provide a good opportunity for air to escape. Ensure that cylinders are supported and rod travel is unrestricted. When performing the cylinder cycling process: Ensure that cylinder snubbing does not occur in the first six extend and retract cycles. When the rod is fully extended, extreme pressures are achieved and can cause dieseling. Do not stall the cylinder. Do not allow relief valve to open. Cycle cylinders SLOWLY. Move cylinders as slowly as the machine will allow. Do not rapidly reverse rod travel direction and wait 4 seconds before reversing travel for all cycles. Perform the following cycles: For the first six cycles do not fully extend or retract the rod. Use a maximum of between 1/2 and 3/4 of the stroke to extend and retract the rod. Perform four more cycles fully extending and retracting the cylinder but under the conditions of Step 6. Once this procedure is completed, all the air should be purged from the cylinders. With no air remaining in the cylinder, no further special handling is required.
Thanks for everyone's input Ok, so I've been working on this for a while now and have been following 92U/funwithfuel/niges instructions and one cylinder it worked perfectly on, the other is acting odd. Cylinder unhooked, laying horizontal, fittings up, low idle, starting from center of stroke, working gradually out to full stroke over the course of about 100 cycles. In this position the cylinder seems to get completely bled (moves nice and slow/smooth even at full throttle) hook it back up to the machine and it moves way too fast and violent, until it hits the last little bit of fluid at the ends of the stroke and slows down. Did the entire procedure twice and same results. This is just a regular 2" bore x 4" stroke welded cylinder, with a .031" restrictor fitting in one of the ports. All new parts, cylinder, spool valve, hoses, etc. Even when hooked up and acting like it's full of air it doesn't drift at all, so I don't think a seal is bad. Thoughts?
Are both cylinders on the same spool or does each have its own valve? Could it be one spool is closed to wide open with no lead in cuts, while the other has a lead-in.
Which circuit? Any anti-cav valves or something like that on the circuit?
Each on a separate circuit, it's a Shaver HD10 post driver that I converted to hydraulic tilt/angle. Copied their design exactly, new Prince monoblock three spool valve, first spool is single acting (raise/drop hammer), second spool is double acting fore/aft tilt (the problematic one), third spool is double acting side to side tilt. Below is a picture of a new HD10, mine is basically the same except both cylinders have the fittings on top and I used JIC hoses/fittings. I do also have a second set of valves mounted below the pictured one to control top and tilt on the tractor for more range of motion, but that should be unrelated to the problem:
Have you tried without the flow restrictor to see if it works properly? Wondering if the flow restrictor could cause air bubbles in one direction or restricts the flow too much?
I can pull the flow restrictor out and try to bleed it, but I'll have to disassemble to put it back in which will reintroduce air into the lines. The geometry and small size of the cylinders make the functions move dangerously fast without the flow restrictor (tried that when I first put it together). I might try moving the flow restrictor to the other end of the cylinder and see if that does anything.
Welder Dave brought up a good point. That orifice could be foaming the oil/air making it near impossible to purge the air out.
I will try removing the orifice and see if I can get it bled for testing purposes. Would installing the orifice at the valve end of the circuit vs the cylinder end help the situation at all?
I don't know, and the whole theory is speculation. I could see air/oil forced through an orifice would cause foaming or aeration which is obviously a combustible mix. Is there a possibility that the pump just has too much flow? Just spitballin here, throwin out ideas.
I wonder if flow restrictors have max. flow rates they can properly reduce? I mean if you wanted to slow 100 GPM down to 2 I don't think it would work. It sounds like MG might be turning the flow into something like a pressure washer that is sure to cause aeration. Maybe a 2 stage flow restriction would work? Do you know the hyd. flow of the tractor?
Definitely not too much flow, we regularly run these HD10 drivers on tractors or skid steers with 10-20 gpm hydraulic flow, the tractor I have it mounted on is only 5gpm. The way I have it setup is nearly identical to the factory hydraulic setup Shaver uses on these drivers (restrictors and all) and they work fine. So I'm not reinventing the wheel, I just must be missing something. The only other thing I can think of is this new tractor runs Kubota Super UDT hydraulic oil which is about the consistency of water, not sure if that has anything to do with it. Everything we've run post drivers on previously has used regular Kubota UDT, JD Hy Gard, or the like.
Any feedback from the manufacturer? Just a friendly phone call? Hi, I recently set this up and I'm experiencing this... any thought or suggestions. They may have been down this road before, many times over. Years back we had a crane mfr whose extension cylinders in the boom would chatter like mad. Ultimately, they had us change to 56 with an additive package, no other physical changes, and it stopped. That was with a full power boom not pin n latch. Chatter with a load was a no-no!
Ok so I *think* I got it, will double check tomorrow to make sure it's still bled, but so far it seems good. The problem was indeed the orifice restrictor or it's location. I took it out, bled the cylinder, then installed the orifice at the valve end, bled again and it seems to have worked. Based on yalls theories and what I can figure, it was either aerating the oil or trapping air and due to the location it just couldn't get out. Once the system was properly bled, some air did get reintroduced, but since the orifice was directly at the valve it was much easier for the air to escape. From now on I will install any restrictors at the valve end, unless there is a good reason not to?
What’s worked best for me is: extend cylinder fully, crack rod side hose and start retracting cylinder until no air is seen then tighten hose. Retract cylinder fully then crack piston side hose and start extending cylinder until no air is seen in oil and tighten hose. Repeat several times if necessary. If the seals in a cylinder are good and not leaking either internally or externally, I can’t really see how else you could get the air out?
Well that brings back some very real memories I'd forgotten about, had that identical unit 30 years ago and went through those same issues you just did, sorry I never saw this thread in time to help you out. When we had hose or cylinder issues we'd leave the fittings loose then cycle them till oil came out then tightened the fittings up. With the orfis restrictors in place anywhere but near the valve it was impossible to bleed the air out. I can't recall now but I think the unit we had used two restrictors per cylinder one on each port and I think we took one out and only restricted one side but I don't remember which side of the cylinder stroke we put it on. The happiest day I can recall was when that shaver post driver left and we started using a Deere crawler loader to shove posts into the ground instead for the steel t posts and digging wood posts in with an excavator, 10 times faster and so much easier the only down side it was no longer a one person job but a three person job. One to run the crawler loader one to run the skid steer that carried 100 plus posts and third to handle the posts for as fast as we put them in. Over the years I've blown apart several hydraulic cylinders due to trapped air usually small cheap cylinders that have aluminum end caps or very low grade metal, the issue I've had is air compresses and oil won't, meaning if you have oil on one side and air on the other one side can compress the air without moving but when it does can move at tremendous speed. So if a cylinder is new or rebuilt with no oil in it, the seals will take some force to move but once moving they can move fast,so fast if it's to extend can crack the end cap. So whenever we install a new or rebuilt cylinder we squirt oil into both sides and pull and push them by hand to cycle them and I like to leave them fully extended and cycle them to retract first so the side with the cap on is full of oil to help eliminate this issue. The longer a cylinder sits on a shelf somewhere the worse the potential is if that makes sense, with larger cylinders this has never been an issue but after you blow the end caps off a couple small 2 inch or less cylinders you tend to be wary and make sure they move by hand first, part of the reason for starting at half stroke and moving each direction a little at a time is to help eliminate this issue, once you have some oil on each end you no longer have metal hitting metal but oil to help cushion things when air compresses and when things do start to move very fast, you don't have metal hitting metal.
Thanks for the reply. Moving the orifice to the valve end solved the problem. I wouldn't have thought it made that much of difference on which end it was in, but obviously it did. I've been building fence for almost 25yrs now and I've tried a couple different fairly expensive European and Australian tractor mount drivers, skid steer mount drivers, about everything short of the new self propelled track units, and I've come full circle back to using a Shaver HD10 on a small 4wd HST tractor. These newer Shaver models are so much better than those old ones I remember from decades ago. They extended the mast so it has a solid foot that rests on the ground which takes all of the slop and jarring out of the unit. This alone made all the difference in the world being able to drive straight posts. In addition to hydraulic angle and tilt I've added 12" of side shift and 12" of fore/aft shift. On a small tractor that's easy to get on/off it makes for a pretty decent unit for one man operation. Best I have come up with so far that doesn't cost $100K+
I have no idea how many miles of fence I've built over the years and I too tried many different things, all really took two people to get much done and not walk yourself to death or climb on and off a machine 500 times a day. When I bought my first crawler loader we started to use that and never looked back. When we added a skid steer to the equation then the hydraulic wire winder to fit that we could roll up the old barbes, string all new wire and replace any broken posts and use the crawler loader to take out trees and brush, then after tightening the barbs one person sat in the skid steer bucket as the second person drove along the fence as the one sitting in the bucket installed all the fasteners saving miles of walking and bending over as the third person picked up old posts and rolls of wound up wire and picked apart fasteners to hand to the one putting them on. The best part of the whole deal the other two helpers were my kids or as some refer to them cheap labor so depending on which one's upset me or their mom the most that day determined who was helping me and what job they got assigned snd for how long, I guess today it would be considered child abuse but the centuries before it was called life and learning job skills and how to work. That and my wife also used it a lot to eliminate whining and complaining and things not getting done around the farmstead because all she would have to say is "if you won't or can't get whatever done you can go help your dad and take one of your siblings places putting in new or fixing fence". She also kept record so once spring fencing season was over if you upset her anytime during the rest of the year she not only kept track of how many times but also the duration of time that kid needed to help Dad while fencing the next year. Needless to say I never had to ask who was helping me fence I was pretty much told who was helping me and I'm also pretty sure why one son signed up for the marine corp while he was still in high school, it was that or helping fence for the next 200 years or his mom passed away whichever came first.