Got a mini with a thumb that's operating slowly. It's got a D-03 valve on a "Power Beyond" Block. I'm less than happy to admit ignorance when it comes to hydraulics but it'll soon be evident. I know what the D-03 valve does but I don't know how. As far as the PYB goes, I understand it takes pressure from one function and robs it for another. It blocks the donating function while the parasitic circuit does it's thing. There are three relief valves on the block- Three hoses coming into the block and two out to the thumb cyl. So there are 5 ports on the block- "P" which I think is pressure, "PYB" back to the donating function (?) "T" to the tank (return?) . The outputs are "A" and "B" which go out to the thumb. My hunch is that one of the reliefs is bad. What I don't know is why there are 3 reliefs? On top of that, I know what a relief does and know how to adjust one but don't know how it works. Does it back pressure up from the return side and let go at a prescribed pressure or, something else.? Lack of knowledge is enough to drive someone to drink, which is exactly what I've done. Here are some pics:
Wait a minute, I gotta get something in my head. Do you simply flip a switch to make the thumb operate? Or do you have to operate some other function, stick, or pedal while operating the switch as well?
Rob i have never seen a valve just like that one but i think your looking at two circuit reliefs and one power beyond. The pwb port should feed another controll valve down line then return's to tank. Do you know if it's a open or closed center system. Both systems use pwb just set up differntly.
Some how the D-03 controls everything, there's a switch on the handle that works the 'open and close' - switches the D-03
Sorry Steve, I can't wrap my head around your post at the moment.
What brand of hoe is it. So your saying switch open everthing hyd works and closed nothing hyd works is this valve factory or something someone has installed.
The pump flow is taken from the main valve outside of the spools. There is probably a plug removed and an adapter fitting plugged into it and a hose runs from there up to your auxiliary valve block. The D-03 valve is the electrically actuated pilot control valve on top of the aluminum valve block. The two cartridges with the long screws probably house a spool valve. The screws control the maximum amount of stroke each way that the spool can move. The relief cartridge is most likely ported from the input to the tank return. Energizing one side of the D-03 sends pilot oil to one side of the spool in the aluminum block that then opens and sends oil down to the thumb cylinder. If you look straight down at the center of the D-03, there should be a hydraulic schematic that explains the operation of the pilot. I think in the photo I see the lock nut gone from one of the limiting screws for the main spool. If that spool moves too much one way the oil will find somewhere other than the thumb cylinder to go to. Let us know what you find when you check it out.
It's a gray market Komatsu PC30 MR-2. I think the valving was installed by a rental outfit. Everything works fine Steve but the thumb (which this mess operates) is slow to open and close.
Yeah, I noticed that nut missing too John. I just wanted to know how things worked before I started turning screws or swapping reliefs.
pressure reducing valve?? Looks like you may have a pressure reducing valve and two circuit reliefs. The reducing valve will "step down" the main system pressure for an individual circuit much like a air pressure regulator does. If you could post some valve makes and model numbers it would help. Tom
I had same thoughts as John C. It's an internal pilot solenoid valve and the opposing adjusting screw cartridges determine how far the spool shifts. I'm thinking the Y port is a separate tank port to provide tank drain for internal pilot circuit and not be affected by spikes in pressure and flow on the T port.
BTW Rob, power beyond typically, but not in every case, is used to describe the configuration of the tank outlet port of an open center hyd valve and how it sends oil to down stream valves from the tank port of valve. Yes, that solenoid valve may be fed by a power beyond circuit, but it doesn't care where it gets its oil supply from, that's why PBY is more reflective of valve supplying the oil than the valve receiving it.
The one missing the nut is screwed pretty far out which the nuts are jam nuts i might try measuring how far its out then slowly turn it in some and see what it does.
Hi. It's been a while since I have thought about closed center hydraulics. Could the third line on the input side of of the manifold be some type of load sense to stroke the pump when the the thumb is operated without any other function? If so, perhaps the third cartridge is associated with this.
Good point brian, being a mini ex, it should be a closed center system, I totally overlooked that. Very interesting valve arrangement. BTW, welcome to the forum. :usa
I've not seen the closed center systems on Komatsu minis. I don't think this one is load sensing either. Many of these machines have two gear pumps installed. The later models as I recall have the piston pump but were pressure compensated on the top end. As the pressure got over a threshold, the pump output gets cut back by that pressure. More than likely this is an open center system and may have negative flow control of the pump. Basically all the valve spools are open center to the bottom of the valve which has a restricted flow back to the tank. When all the valves are centered there is a small hose that goes back to the pump which tells it to destroke. When a valve is stroked that oil goes away from the outlet on the bottom of the valve and pressure drops which puts the pump back on stroke.
The thumb is slow but does the thumb have good clamping force.
I've been thinking about this valve all day. I still think John C is right, it's an open center hydraulic valve. As for the markings on the valve, hyd valves typically go like this: P is pressure supply port to valve. T is tank return port. A and B are work equipment outlet ports to actuators such as cylinder, motor, etc. X (which you don't have) and Y are typically pilot circuit ports. Here's my best guess about that valve Rob, I'll try to explain it in some understandable fashion and the other pros can tell me if I'm all wet. The aluminum block is typically called a manifold. A manifold is used for a variety of valve and function configurations. This particular manifold is for an open center 4 way valve. All that means is when the valve is in the neutral position (no functions being operated), oil enters the P port and flows right through the valve to the T port to return to tank. 4 way basically means it has 4 ports to control oil flow in and out. The manifold is fitted with a main relief valve to dump excessive pressure on P port and send it to T port to return to tank. The output to A and B port would be controlled by either a spool in the manifold, or some form of valve within the two cartridges on opposite side of manifold. My guess is a spool, but can't confirm that. In either case, spool or cartridge valve, it's controlled and operated by internal pilot ports that connect spool/cartridges to the solenoid valve mounted on top of the manifold. That solenoid valve is what had me puzzled, then it dawned on me. Remember, the solenoid valve operates the spool/cartridges by directing pressurized oil, via internal pilot circuits, to act against the spool or cartridges and shift them. Being that it's an open center valve arraignment, there is no real standby pressure on the P port to operate the pilot circuit within the solenoid valve. That's where the Y port comes in. The Y port is likely connected to the pilot circuit of the excavator controls, the circuit that the joysticks use to control the main valve and such on the machine. That way there is pressurized oil to operate the solenoid valve circuit regardless of pressure, or lack of, on the P port.
old dowg/new technology Thats Slick Willie and John, couldn't resist saying that-if you all are corrcet about a spool being in the manifold and the adjustments on either end limiting the stroke of the spool it would be equavilent to the industrial subplate mounted DCV-notice the high-tech threaded rod and locknuts on the endcaps where you can limit the shifting of the main spool. Can't say where the Y ported hose is terminated but it should go directly back to tank unrestricted-Y will always be pilot DRAIN and X will be pilot PRESSURE. You maybe on the right track if this is an open center setup as you will need a MINIMUM pilot pressure in order to generate enough force to shift the main spool, in industrial applications this is around 100 psi-an appropriately size check valve is generally installed in the pilot pressure port of the main body to insure enough pressure. I hope this file uploaded showing the Vickers two stage valve. Tom
HydrauMind (Hydraulic Mechanical Intelligence New Design) system, closed-center system with load-sensing and pressure compensated valves. If im not mistaken thats what your dealing with.
Rob, you're a little slow out there. By the time you give us some info to work with, we're already gonna have that valve on a launch pad flying the space shuttle. Bah ha hahahaha :tong
That's kinda what had me hung up Maytag, I knew X was typically for pilot pressure and Y is typically pilot return, just puzzled over the configuration. Do you suppose that's not a main relief valve on the P port and is instead a pressure regulating valve of sorts that holds the required PSI on the P port to operate internal pilot porting? Would make more sense that hose connected to Y is a separate tank line as then it wouldn't be subject to pressure spikes on T return line which could affect pilot valve spool operation.
When I have the option (not all manifolds are ported for Y) I will always convert to external drain for a pilot operated valve. Tank line pressure on a big industrial system can spike to several hundred psi-enough to shift detent valves. This is one of the first things to rule out when troubleshooting-kind of comparable to a bad ground and unexplained electrical problem on a piece of mobile equipment. Tom
Willie59 I bet Rob has already fixed it and is messing with all of us.
Or he's working on that 70's model RD350 Yamaha. LoL
Sorry, I didn't have time to work on it today. I did talk to someone that said the third cartridge might be a flow restrictor. We'll see.
LOL, How did you know :cool2
I'm Yoda.
Usually the valve spool in the aluminum block is closed center because the oil from the machine main control valve is taken from a power beyond port. If the spool were open center, then none of machine functions would work as all the oil would be flowing out the power beyond port and back to tank. I don't recall seeing a PC30MR2 with Hydramind but I sure could be wrong about that. If it is then this whole setup is being run closed center and oil is being robbed from somewhere it probably shouldn't be. It is possible they are robbing oil from the blade circuit which as I recall is run off a gear pump. Those machines are pretty tight, so it may be difficult to trace the supply piping back to the source.
Rob my buddy had one they were good bikes i think he might still have it in a shed. He had a set of expansion chambers for it but dont think he ever used them. They just had a sound of their own.
And THAT is one thing that is certain.
John I havent worked on any pc 30 mr2 machines but i looked up the machine on komatsu like a sales page with specs and it talked about the Hydramind set up. If the blade is off a positive displacement gear pump and there coming off it to the thumb valve would be open c . Check out komatsu specs page on the Hydramind part. If the blade and thumb are on a gear pump open c. The three valves could just be two circut reliefs and a main relief with no power beyond. That would explain 3 hoses in and 2 out also. The one screw that looks to be way out with no jam nut could be the main relief for that manifold. If the pilot valve and manifold just had brand/#s .
They can run this a bunch of different ways depending on the system supply. The block looks a little home made which is pretty common in this neck of the woods. We have several shops in the area that will build a valve block for any odd application. I hope Rob has time tomorrow to do some exploration.
Not to be devils advocate here but did anyone see of the valve in question is even for an open centered system, let alone what gallons per minute valve it is, maybe the reason for everything being slow is because its too small of valve to begin with, the reason why the lock nut is off and the adjuster is screwed one way is so they could get some more flow to make it work faster, you know like any idiot trying to make something work thats not right to begin with. If some rental shop did it whats to say they knew anything about hydraulics to begin with and even started with the right valve? I'd opt to do this in reverse, first see whats needed and how it should have been done to work properly and then see how it is done to double check it was done right, how many gallons per minute system are you working with and how should it have been plumbed? Not to say I know anything about anything but thats where I usually start on any add on system done by anybody thats not working properly. Do you have any idea if it ever worked right? How about a flow regulator installed to see whats what and where things are actually going and at what gallons per minute and pressure, then compare it to how things should be and where they are going, we can discuss a lot of scenarios but until we know something that's actually happening how can we diagnose anything as to whats wrong? Again I'm by no means any expert and feel free to call me a moron at any time, I get that a lot at home anyhow but to me this is how I'd go about the situation and problem at hand. I did like the explanation of how the systems are supposed to work though and where they are supposed to go and how they preform, and it was in clear understandable english even I didn't get lost, so thumbs up on that part guys.
Randy i agree he needs to find model and numbers off the valve and see what he's got and what its on. If that is a main relief the screw is backed out of it isnt going to increase flow backing it out its going to lower pop off pressure and the valve might not even be seated or seated so lightly that half the oil is returning to tank and residual pressure is what the thumb is working off of. If that was the case the thumb wouldnt have good clamping force though. Everyone on here does have good knowledge and without info its hard to figure.
There are no numbers on the block. To me, it doesn't look factory. I checked the pressures and the relief that looked like it was turned out was at 200psi. That was the open function. The bite was at 1800. I Set them both at 1500. It now works as good as it ever has but it has always been somewhat slow as far as I know. Maybe it's by design? The third cartridge was turned almost all the way in so I backed it off and it made no difference. I took it out thinking it might be a bad oring or something but I didn't see anything.
I wish you lived closer Steve, I'll be looking for another one when I'm done with mine. I have expansion chambers, hope to hear the "ring ding ding" next spring.
So with three cartridges you basically have a Drac valve. It is a pressure control only and apparently the D-03 valve on top is for show.
That cartridge looks like a relief valve to me. Hey Rob, are there any markings on those cartridges?
Willie i talked to Frank Baria from heavyquip a few days ago hes a mess. Rob thats good you got the pressure up and it working. Seems you have a flow issue also. Make sure you got correct voltage and no cobbled up wiring causing a resistance going to the solenoids. The thumb imo should move as fast as the blade goes up and down. Are the cylinder,valve block, ports compairiable in size and the hose inside diameter. Also check for restrictor orfices in cyl,valve block, and where feed and return hoses are coming from. The picture of you holding the valve thats a compression release off a Bultaco quit messing with us.
Now that's funny. LMAO
I thought you would like that. Willie i appreciated you time the other day on the lull parts. Got everthing at tiffin parts and they are a good source for the lull's. Steve