hydraulic help

[Bob Vavricka]

Is there anyone on the forum that is an expert in hydraulic systems or who can point me to a source for troubleshooting a problem. I belong to a Kiwanis Club that runs a small train in a kiddie park that uses hydraulics for a drive system. It is a shop-built train that was converted to run on hydraulics about 10 years ago and we are have replaced the control valve and motor. It used to free wheel when you let the control valve go back to neutral, now the wheels lock up when you let back on the control valve so I am looking for some technical assistance on our problem and thought I would try here. It us amazing to see the range of expertise of forum members.
Thanks,
Bob Vavricka

[Steve Rozmiarek]

Bob, it quit working after you changed the valve? The reason it doesn't free wheel is that the oil is stopped by the valve when you close it. If it worked before with this valve, you have a check valve messed up. If it never worked with this valve, it's the wrong valve or some adjustments need made. Have some pics?

[Tom Stenzel]

If the problem started with the valve replacement, the replacement valve is what would be called "closed center". The ports that go to the load (hydraulic motor in your case) are blocked when the valve is allowed to go to the center position. If you want to allow the load to move freely you are looking for an "open center" valve, where the load ports are both connected together and open to the tank line.

For a hydraulic motor you simply need the ports open to each other. All open center valves also open to the tank, as they don't know what the valve will be used for. For instance, a single ended cylinder, like what you would see on a logsplitter, changes it's internal volume as portions of the rod leave and enter the cylinder. The tank port is left open to allow oil to flow in and out. Otherwise the cylinder would still be locked even with the ports on each end hooked together.

the other consideration is if the pressure port is open to tank in the neutral position like found on a backhoe, or blocked to maintain system pressure like found on machinery. In your case I *THINK* you want the pressure open to tank to reduce prime mover (the engine running everything) loading and heat. That may not be true as I don't know what else is going on in your train. I also don't remember the naming for that type of valve out of the top of my head.

It's been 35 years since I worked in a hydraulic shop so I'm not up on what's currently out there for manufacturers or parts.

-Tom

[Tom Stenzel]

Just to prove that decades of time and a year and a half of chemo can rot the brain, it looks like "open center" refers to the pressure port being open to tank in the neutral position. I got that wrong.

I'm still casting about for the correct terminology for having the ports open to each other and to tank. But that is still what you're looking for.

I remember valves with the ports blocked being much more common. What you have is what would be required on a backhoe.

-Tom

[Bob Coleman]

I think this is what Tom is saying: When in "drive", the valve has both the hydraulic supply from the pump and the oil return to the tank open. Your old valve, when shifted to "neutral", shut the supply line and left the return line open. The new valve shuts both the supply and return lines. At least this is how I interpret it in USN hydraulic speak.

If you look on the valve it should have little arrow symbols that show what I described.

[Jerry Bruette]

I think Tom has it right.

With the pump running and the valve in the neutral position, oil goes from the pump to the valve and through the valve back to tank.

With the pump running and the valve in your "forward" position the oil goes from the pump to the valve then to the hydraulic motor, turning the motor so the train goes forward, then back to tank.

With the pump running and the valve in your "reverse" position the oil goes from the pump to the valve then to the hydraulic motor, turning the motor so the train goes in reverse, then back to tank.

You should also have a system pressure relief valve that would relieve pressure to tank should something go wrong, along with a valve that would set the system pressure.

Jerry

[Tom Stenzel]

I tried drawing -using my best guesses- what your 4 way valve is doing, and what you want it to do.I hope the PDF explains more than it confuses.

The little squiggly line at each end represent springs, so that the valve will move to the neutral position if you let go of the handle. There may be detents to hold the valve in a position but I didn't put them in my drawing and I don't remember the symbol for them anyway.

If this uses an electrically operated valve, then there will be a box with a smaller rectangle with diagonal line through it on each end of the valve.

The drawing is a bit crude, I used Openoffice to draw it. Man, talk about eating your own dog food...

-Tom

[Steve Rozmiarek]

Tom, I think the term you were looking for is float. Jerry called it neutral, but referring to the same thing. Curious what valve Bob is using, there are a bunch of different valves out there.

[Mark Bolton]

Steve's got your answer. You need a valve with a center float. It's not open center. The. Float position opens all ports to tank which in your motor scenario would be like throwing your car into neutral.

[Tom Stenzel]

Mark has it right.

Boy, did I botch up my terminology. Started off wrong, then wandered off in the bushes. Using "float" in a search I came up with:

http://www.enerpac.com/en-us/valve-information

What I called open center Enerpac says it's tandem center. I don't remember that at all!

No relation to Enerpac, the link does have diagrams and names for the different valves. Open center is what you're looking for.

BTW, I looked at the Northern Tool site, they have lots of valves but the descriptions were useless.

-Tom

[Steve Menendez]

I don't want to be the one to specify the wrong valve to you, but can wholeheartedly recommend Grainger and McMaster-Carr as suppliers of hydraulic goodies. Our Facility Maintenance Manager uses those 2 companies extensively for hydraulic hoses and controls.McMaster Carr (www.mcmaster.com) has a particularly good technical description to accompany almost everything they sell.Steve.

[Bob Vavricka]

Thanks for the replies. More information concerning the system. The hydraulic pump is powered by a 22 HP Air Cooled Honda Engine and the fluid runs through a filter and cooling radiator before going into the control valve. Between the control valve and the motor "was" a crossover relief valve. The motor is a Char Lynn 104-1026-006 motor that drives the wheels through a sprocket and chain to the drive axle.
It has worked fine for about 10 years. What changed? We had a decrease in power and in troubleshooting it as best we could determined the control valve was letting fluid bypass. The control valve was a Hawe control valve that had both electro-hydraulic and manual actuators. The electo-hydraulic was supposed to give us the ability to set ramp-up and ramp down times, but never worked as we expected so for most of the time it has been used with the manual lever. If I am reading the information right it is an open-center control valve.288596 This is a link to the information I found on the valve. http://www.hawe.de/fileadmin/content/typeman/catalog/Pdf/7/7/D77002-en.pdf This valve was replaced with an basic open center control valve with an internal bypass valve that could be set between 1000 and 3000 psi and is currently set at 2500 psi.
After replacing the valve we still did not have enough power and the rep from the place where we bought the control valve indicated that since the control valve had a bypass valve, that we did not need the cross-over relief valve so it was removed--I think that was our mistake. Removing it did not solve the problem. The fix was a new hydraulic motor identical to the first. So what we have now is the new control valve and no cross-over relief valve. I believe re-installing the crossover relief valve is what we need to do. However if that is true, I can not find information on how to adjust it. The original adjustment has been changed.
My questions at this point is do you think the cross-over valve missing is what causes the wheels to lock-up? And can anyone point me to information on how to adjust it if I put it back in. The cross-over valve has Oil Control, Italy Modena on it and the number 051501035720000 on it. I believe the company is now Boschrexroth. 288597.

[Tom Stenzel]

I hope this helps.

Quote: I believe re-installing the crossover relief valve is what we need to do. However if that is true, I can not find information on how to adjust it. The original adjustment has been changed.
My questions at this point is do you think the cross-over valve missing is what causes the wheels to lock-up? And can anyone point me to information on how to adjust it if I put it back in.

The purpose of a crossover relief valve is to prevent sky high pressures caused by a load driving the hydraulic motor/cylinder. Usually these loads are caused by inertia. Where would you find a load with a lot of inertia? A loaded, moving train certainly comes to mind.

Right now your ‘relief valve’ are the steel wheels skidding on the rails. What if the friction was higher and the wheels wouldn’t skid? Then there would be really high stresses in the system- broken drive chain, snapped shafts, burst hydraulic line from the motor acting as a pump and having the oil nowhere to go. The crossport relief valve is there to prevent just that.

Setting it isn’t critical. It typically is set somewhat higher than system pressure, but low enough to prevent any mechanical damage in your system. With it in place and set to a reasonable pressure, you won’t lock up your wheels but you will get a high braking action. Setting it lower pressure than your system relief valve will result oil from the pump bypassing the motor, reducing available torque.

The electo-hydraulic was supposed to give us the ability to set ramp-up and ramp down times, but never worked as we expected so for most of the time it has been used with the manual lever. If I am reading the information right it is an open-center control valve

I looked through the Hawe valve PDF and can’t find where any ramp up/down option was available. I could have missed it, the English translation is awful. What the valve provides is a proportional current/flow, where the flow varies with the current. Valid current values are 0.2 amp to 1.0 amp at either 12 or 24 volts depending on the coil option.

It doesn’t help when Hawe describes the valve as open center when it has the pressure relief valve option (PSL model) and closed center when it doesn’t (PSV option). It will allow the motor freewheel in the center (neutral) position if it has spool option H or O (see table 14 on page 11 of the PDF). For inertial loads they do have an optional valve (regeneration as they put it, /32 DFA or B option see page 12) but if you have it i THINK you would lose reverse in your system. I think that’s what Attention: Not suited when pulling loads are anticipated! is trying to say, and the way the valve is piloted seems to confirm it.

This valve was replaced with an basic open center control valve with an internal bypass valve that could be set between 1000 and 3000 psi and is currently set at 2500 psi.

If the valve is truly open center the motor should freewheel in the valve’s center position. System pressure would also fall off as the pressure port is going directly to tank ( I’m using Enerpac’s terminology now).

Myself, I would reinstall the Hawe valve, there probably is nothing wrong with it.

-Tom

[Bob Vavricka]

Tom,
I appreciate your detailed reply and the time I know it took for you to compose it.
I didn't give you enough info about the ramp-up/down feature. It required a remote handle and circuit board controller which we never got to work right (ten years ago). So we used the manual lever. I don't think that made any difference in the overall operation of the system.

The Hawe valve has an H in the numbers on the body and as best I can decipher their info that indicates the flow pattern which seems to agree with what you think.

I am pretty sure the valve we are using now is an open center valve if I understand it right (and I may not). I put a pressure gauge in the line between the pump and the valve and with the control valve in the center position there is not any pressure showing on the gauge, so I think the oil is going through the valve and back to the tank. Am I correct in that is how the open center works?

I will re-install the cross-over relief valve tomorrow and see how that works. There are two relief valves on the block that the lines attach to. One for the line to the motor and one for the line from the motor. From your comment about the relief valve, I will set the one from the control valve to the motor a little above the working pressure in the system so I get full flow to the motor. What about the one on the line from the motor to the valve? Is it set the same and serves the same purpose in reverse? We rarely use reverse on the train.

I'm still confused about how the open center allows the train to freewheel in the center position if both the A and B ports are not getting fluid and the pressure from the pump is returned to the tank through the valve.

I will consider reinstalling the Hawe valve if necessary, since I believe our initial problem was a worn motor and not the valve.

Again, I really appreciate your time and patience with my questions.

Bob Vavricka

[Tom Stenzel]

288737288738

I will re-install the cross-over relief valve tomorrow and see how that works. There are two relief valves on the block that the lines attach to. One for the line to the motor and one for the line from the motor. From your comment about the relief valve, I will set the one from the control valve to the motor a little above the working pressure in the system so I get full flow to the motor. What about the one on the line from the motor to the valve? Is it set the same and serves the same purpose in reverse? We rarely use reverse on the train.

Typically both valves are set to the same pressure. It’s meant a a safety device, you have all the same forces in both directions. Remember, setting it too low will cause no damage. The motor may not run correctly (loss of torque or power) but nothing will be broken. That’s an important start.

I'm still confused about how the open center allows the train to freewheel in the center position if both the A and B ports are not getting fluid and the pressure from the pump is returned to the tank through the valve.

I drew another picture. Instead of using names, I called them valves 1 through 4. Why? Because I can’t find consistency with the names. Hawe and Enerpac conflicted with names, and Mark in his post conflicted with both. And I’ll bet he can pull up a source that says he’s right! I’d prefer not to argue the names and just deal with the functionality.

Valve 1 has all ports closed off in the center position. Included only because I already had this drawn.

Valve 2 has the pressure port hooked to tank in the center position, with A and B both sealed.

I’m sure your replacement valve is acting this way. Where would a valve like this be used? A log splitter or a hoist. When the cylinder isn’t working you absolutely don’t want it to be able to wander around. Having the oil pump dump to tank with no pressure while not being used avoids a lot of heat. Then you don’t need an oil cooler at all. Plus a recoil started engine might have a chance to get running. It’s a very common valve.

Valve 3 in the center position has the pressure port sealed with A and B and the tank lines all tied together. This is probably how the Hawe valve is configured. This will allow the motor to free wheel and system pressure will be at the relief valve setting in the center position.

Valve 4 opens up all ports, A, B, pressure and tank together. Your motor will freewheel and the system pressure will fall with the valve in the center position. If your hydraulic system is doing anything else besides running the hydraulic motor then this valve can’t be used.

A question you might have is, if the oil is free to travel through the valve in the center position, what is the point of the crossover relief valve? And, you would be right, oil should never go through it. But it is a safety device, it’s there if something goes wrong.

I still wonder why the Char Lynn motor failed. I mostly saw the H series (101-) gerotor motors. They didn’t like side loads like sprockets and pulleys as they relied on a hydrodynamic bearing for sideloads.But your 104 series geroler has some substantial rolling element bearings that can take a pretty high radial load. Couple things come to mind.

If you don’t have a case drain, install one. It helps with the lubrication and at 2500 PSI system pressure you’re close to the limit of not having one. Also if you have a high drain flow it means the motor has high internal slippage and is worn out. It helps with diagnosing problems.

Try to place the sprocket as close to the motor (away from the shaft end) as practical and keep a straight chain line. The attached PDF (lifted from the Eaton manual) shows you can raise the side load limit by 20% by moving the side load from end of the shaft to the middle.. Since you can’t change the amount of side load placing it where the motor can best handle it would an improvement.

Check your oil and filter and clean things up if needed. 10 years of seasonal use on a Char Lynn? I would expect better. They’re rugged units.

-Tom

[Bob Vavricka]

Tom,
I don't see the pictures of the valves you drew. If you can post it I would find it helpful and others following the thread may also find it instructive.

You are right, what we have is your valve #2 which Prince calls a "tandem center spool." I found that they also make one called a "motoring spool" that is like your valve #3. I believe it will work for us because the hydraulic motor is the only thing we are using the hydraulics for. I'm still not sure what the Hawe valve is, but it has an H on the id plate that is in the Flow Pattern position and is shown in Table 14 of the pdf file I linked to in an earlier post. I don't think it is your valve 4, because I think we would have heard a different sound from the valve in the center position as the oil went through a bypass valve. We didn't have a pressure gauge on then so I don't really know what the pressure was when the valve was in the center position.

Tell me more about the case drain. Does it connect back into the hydraulic system or just vent to the outside? I think I will see if we can operate at a lower pressure. The new valve will be factory set at 1500 psi and I think I will use that as a starting point and see if it gives us enough power. I know this will require adjustment of the crossover valve also.

About the early demise of the Char-Lynn motor-You have to understand that this is an all volunteer organization and that the train has had different maintenance people over the years and some have left the club. So the maintenance has been spotty at best and it doesn't help when someone decides that the hydraulic tank is the gas tank and puts gasoline in the hydraulic fluid. So the question may be, How did it last this long? We have had consistent maintenance the last few years and the filter and oil get changed on a regular schedule and we beefed up the training for our operators along with a checklist before operating. In Oklahoma the State Department of Labor, Safety Standards division inspects all amusement rides and the training logs are required, which is a good thing.

I wasn't aware that the distance the sprocket was from the case made a difference in the side load. This is good info and fortunately our is close to the case as it lines up with the drive sprocket on the axle.

I did find a local person who is knowledgeable in hydraulics and he came by and looked at our setup. His recommendations are pretty much what you have told me and he is also going to help us get the cooling fan for the hydraulic radiator connected to a temperature switch which we have needed to replace.

Again, thanks for the information and the time you spent on your replies.
Bob V.

[Tom Stenzel]

Hi Bob,

The two PDFs I attached in the last post are at the very top of my post. They’re there, just hard to find. Sorry ‘bout that. This time I did a little better.

With all the options the Hawe valve has, having the pressure port dumping to tank in the center position is NOT an option at all. In all cases the pressure port is sealed off. The valve series is meant to be stacked several deep, then have another stack paralleled in the same system. Having a tandem center valve just can’t happen. What Hawe calls an open center valve is a valve with an internal pressure relief valve. That’s not correct, I think it’s a sloppy translation.

The case drain is just an oil line from the motor back to the resevoir. It returns the under pressure oil that gets past the geroler elements and the spool valve. It’s the same idea as a PCV valve in a sucking up compression ring leakage in a car engine. Most hydraulic motors require a drain line. Gerotor/geroler motors only need them under some conditions.I THOUGHT your 104 ( series 2000) motor always came with a drain port, turns out it yet another option so you probably don’t have one. I’ve attached another PDF, one describing when a case drain is required and where it would be. I think I have the right page. If you have 7/8“ staggered ports I came close.288867

If you reduce the system pressure to 1500 PSI your need for a case drain pretty much goes away.

I’m getting this info from a PDF I downloaded from Eaton, pll_1323.pdf. It’s almost 300 pages long. If you get it using search will find everything you need and a whole lot more very quickly.

One last thing: when I wrote the post last night, everything made perfect sense to me. Reading it today, not so much. When I wrote about the need of a crossport pressure relief, I meant when the valve had ports A and B open to each other in the center position. Without that bit of info reading those three sentences should result in a “Huh?”.

I hope all enjoy riding on the train this summer. And you deserve a really big star for this one. Wading into this when you don’t have a good idea of what’s going on, well, most would have walked away. You didn't.

-Tom