Any hydraulic experts in the house?

I have an open center pump and single acting hydraulic rams making up the leveling system on my bus. The control was a mechanical open center four port valve in the floor. So when you turn the pump on and open a port in the valve a cylinder extends. When you open the valve the other way the open center allows the ram to drain back to the tank and heavy springs pull it the rest of the way up. I want to do away with direct acting  hydraulics in the cab.

I have a surplus electric over hydraulic valve sitting on my shelf. 

It has two sets of four work ports and is open center. I plan to plug the second set of work ports and only connect the actuators to one set. So here is my problem: The work ports are closed in neutral position. My question is, if I run the return to the tank, how do I allow the rams to drain back? I am not sure how the work ports drain back to the tank with this arrangement. Can I assume if the pump is turned off and I re open the work ports to the rams they will  drain back? I would like to answer this without experimenting with 3000 psi of oil shooting into a bucket if possible.

Maybe a picture will help... or not.

In reply to Purple Frog (Forum Supporter) :

Nope.....

If you have a copy of the hydraulic diagram of the bus, and the valve body you have posted here I can probably help you.  Been a while since I've worked hydraulics, though

It appears on my setup that each ram has a port at the top and one at the bottom.  So there are two pressure hoses to each ram. No springs causing retract.

So, it uses pressure to extend the ram through the top port.  Then in reverse it uses pressure to push the ram closed through the bottom port.   Sounds not like your rams.  

But, in your case the springs will push the fluid back through the "extend' pressure line.  So maybe you can just cap the other port.

You can test how your valve works just using an air nozzle and activating one solenoid with 12v jumpers.  But you knew that.

In reply to Purple Frog (Forum Supporter) :

I do and I have but they appear to be pressure compensated and I do not have fittings to overcome whatever the internal resistance is. 

Mr_Asa said:

If you have a copy of the hydraulic diagram of the bus, and the valve body you have posted here I can probably help you.  Been a while since I've worked hydraulics, though

The bus is very simple. Just open a valve, oil flows through, open the valve the other way and oil flows back. But I am stuck on the fact that with the valve I want to use, the work ports are closed in the center position, and being a three-way actuator with a set of work ports at either end, there does not appear to be a way to open one of the sets of work ports back to center to allow them to drain. But my common sense tells me that if the pump is turned off and the work ports are open, they will have to drain back to the tank. Still, I don't want to guess and connect everything only to find I am wrong and the rams will not retract.

Wouldn't it be if you do it that way they would have to drain back to the tank through the pump, not the most efficient way.  

I'm thinking your current system might use check valves on the pressure side just before each valve.  So you could "drain" one ram while the other rams are still under pressure.  That way if you extend one ram too far, you can adjust it without bothering the other rams.

First step is you need a schematic for the valve. For the moment, I will assume its three positions run like this:

     A   B     A     B     A     B

     C    D    C    D     C    D

In that "left" position, assume the C is hooked up to your pump outlet, A to the ram, D to the tank, and plug B. When the pump is on, this will allow the pump to activate the ram.

To return, the valve is shuttled to the right position. The pump is off at this point. The pump is still connected to C, but B is plugged so nothing can leave the valve.  The ram is still connected to A, but the spring retract is forcing the fluid from port A to port D, and D is connected to the tank.

With no power to the valve (middle position), all ports are blocked so nothing is sloshing anywhere and no bubbles are finding a path into the valve or ram.

The above is a common schematic. I do not know all the ports on your valve, but check for labels. You might have the boxes in a different order, since both of your solenoids are on the same side. The function would be shuffled a little bit, but basically the same.

matthewmcl said:

First step is you need a schematic for the valve. For the moment, I will assume its three positions run like this:

     A   B     A     B     A     B

     C    D    C    D     C    D

In that "left" position, assume the C is hooked up to your pump outlet, A to the ram, D to the tank, and plug B. When the pump is on, this will allow the pump to activate the ram.

To return, the valve is shuttled to the right position. The pump is off at this point. The pump is still connected to C, but B is plugged so nothing can leave the valve.  The ram is still connected to A, but the spring retract is forcing the fluid from port A to port D, and D is connected to the tank.

With no power to the valve (middle position), all ports are blocked so nothing is sloshing anywhere and no bubbles are finding a path into the valve or ram.

The above is a common schematic. I do not know all the ports on your valve, but check for labels. You might have the boxes in a different order, since both of your solenoids are on the same side. The function would be shuffled a little bit, but basically the same.

Thank you! It is the arrangement on the right that I am unsure about. I am missing that diagram because I could not identify the valve. (no numbers on it).  So the  valve overcomes internal spring pressure to open the return port when there is no pump pressure? That would explain why I cannot make it work with low air pressure. 

In reply to bearmtnmartin (Forum Supporter) :

For the spring retract, I was referring to the springs on your leveling system. You have two solenoids on each valve section. For many systems, there is a solenoid on each side; one pushes from center to left, the other pushes from center to right. You have two on the same side.  You might have to experiment to see whether that is opposite directions or if both together push to the opposite side.

You likely have a "piloted" valve. The solenoid moves a little system that moves the big system. I am used to pneumatics, mostly, which don't bother with this. Hydraulics work with so much pressure that the little solenoids are not enough.

You have a six position manifold with four valves in it. Check all the port labels and let us know what they are. In one of the unused spots, pull the plugs and see what you can see. Are there any ports on the back or bottom?

matthewmcl said:

In reply to bearmtnmartin (Forum Supporter) :

For the spring retract, I was referring to the springs on your leveling system. You have two solenoids on each valve section. For many systems, there is a solenoid on each side; one pushes from center to left, the other pushes from center to right. You have two on the same side.  You might have to experiment to see whether that is opposite directions or if both together push to the opposite side.

You likely have a "piloted" valve. The solenoid moves a little system that moves the big system. I am used to pneumatics, mostly, which don't bother with this. Hydraulics work with so much pressure that the little solenoids are not enough.

You have a six position manifold with four valves in it. Check all the port labels and let us know what they are. In one of the unused spots, pull the plugs and see what you can see. Are there any ports on the back or bottom?

The double solenoid on one side arrangement is kind of unusual. The ports are numbered with the 8 work ports you can see and the pump (P) and return (T) on the end. The work ports are labelled top and bottom 1A 2A  1C 2C  1G 2G  1I 2I  1K 2K No other labels.

I know the manufacturer of the actuators but they did not make the valve but someone kindly emailed me back this afternoon with the name of the company they think probably did, so I am going to call them tomorrow and hopefully get a drawing. 

In reply to bearmtnmartin (Forum Supporter) :

Awesome. We now have a decoder ring. Looking at my diagram

C = Pump

D = T

A = 1

B = 2

Whether A or B is switched will depend on the wiring, more than anything else, but you can test it with it fully hooked up. One wiring position will run the ram, one will let it spring retract, and one will "lock" it as best as it can. No spraying the shop required.

I will let you know! Waiting for the block off plugs so i can play with it tonight.

So I connected everything and while the jacks go down just fine, they do not retract. I plugged the B ports and hoped that when I activated that side of the solenoid the trapped oil would find its way to the return so long as the solenoid was powered. But nothing happens. If I  activate the pump the same time as the B side of the solenoid the jacks retract somewhat but then the pumps hits the relief and they stop. I feel I will need to direct all the B ports to the return line with a manifold to make it work.  Any thoughts?

I suppose it could be closed center. The listing could have been incorrect. I think they require internal pressure to open? My hydraulic knowledge is all out lying on the table at this point.

I would expect the valve to be closed in the center position of the three valve positions. This is a safety thing so that stopping motion in one direction actually stops, not briefly moves in the other direction and then stops.

Have you tried activating each and both solenoids? (both for one valve position).

The return lines need to go back to the tank without passing through the pump on their return journey.

Yes, in your case return lines to manifold for a single line to tank.

YMMV

Well I tracked down the manufacturer and they were quite helpful. The listing said the valve was open center which is why I bought it. but of course not only is it closed center, it has pilot operated check valves, meaning secondary pressure is needed to force the return to open. But they helpfully sent me ebay listings for the parts needed to convert it so just another $100 thrown into the dumpster fire of a bus repower.....

In reply to bearmtnmartin (Forum Supporter) :

Closed center may not be bad. Power is on to extend. Power is on to retract. When power is off, you stay in the condition you were in (extended or retracted, partially or fully). If you are open center, won't that mean the system can move when hydraulic power is turned off? (self retract or whatever)

I should alos clarify open and closed, since they are backwards from electrical. Open hydraulic allows flow. Closed hydraulic stops flow.

In reply to matthewmcl :

Right now I need to replace the pilot operated check valves with solenoid versions so that I can force the valve to drain in the neutral position.       ( solenoids not powered.) If it was open-centered, there would be a constant return to the tank so long as the pump was running, and opening a solenoid would divert the flow from the tank to the open port. But being closed-centered, when the pump is running the oil will just deadhead in the valve. So I need to use a solenoid valve to force it to open in the neutral position and return the fluid back to the tank.

In reply to bearmtnmartin (Forum Supporter) :

Do you need the pump running if the ram is not extending?  If it is closed centered, you just switch the pump and the extend solenoid at the same time. Pump on = extend solenoid on as a momentary push botton (or similar). Retract is the other solenoid but with no pump needed.

With closed center, you need one hydraulic line to each ram, one line from the tank to the pump (if not submerged), one line from the pump to the solenoid maniold, and one line from a manifold on the solenoid manifold outlets back to the tank.

If you have an open center, you have to run an additional manifold on the "B" ports (B in the schematic I labelled) and an additional line back to the tank.  That is a lot of extra lines to run the extra manifold.

 If starting and stopping the pump is an issue then you need that center open, or perhaps easier, a single solenoid valve as a return from the pump line back to the tank. A single solenoid is likely easier (fewer lines) and cheaper (fewer lines) than modifying and then dealing with an open center, but neither is as easy as a closed center if the hydraulic pump is switchable (electric) as opposed to always running (crank driven with no clutch).

In reply to matthewmcl :

"Do you need the pump running if the ram is not extending?  If it is closed centered, you just switch the pump and the extend solenoid at the same time. Pump on = extend solenoid on as a momentary push botton (or similar). Retract is the other solenoid but with no pump needed."

That is what I thought would happen but in fact these pilot check valves prevent the oil from escaping. So I have to do it the hard way and add a solenoid valve to force the check valve open as per the manufacturer.

I think I am getting confused and I would like to clarify some things.

1. This is a three position valve set (four valves in the manifold to run four rams).

2. Center is closed and the other two positions are something like the schematic I referenced.

3. You can activate to achieve all three positions for each valve.

4. When you activate to the retract position, there are check valves in the system that prevent movement. That is to say, the springs to retract cannot overcome the check valve cracking pressure and nothing moves.

5. This system is to move multiple rams independantly so that you can level the rig when parked.

Am I understanding this correctly?

Can you clarify whether this pump is electric, direct drive on a clutch, or always direct drive?

Edit: 6. This is a piloted valve and the residual pressure in the ram is not sufficient to operate the pilot and allow the ram to retract.