Hydraulic plumbing Q?

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I'm trying to figure out how to pull some hydraulics off a dead forklift to use on my Kubota with rear remotes and was hoping I could get some help in understanding how it's plumbed. I've attached a sketch of how it's plumbed, for a visual.

The forklift has a valve that raises the mast, and another valve that angles the mast, both are Parker VDP valves. The angle valve looks to be like a normal DA cylinder valve. The mast valve is a little funky. Well, first, there is what looks to be 2 pumps running piggyback off the same shaft. A small pump and a big pump. The "out" of the small pump runs to the angle valve and the "out" of the big pump runs to the mast valve.

One thing I don't understand, is that a line runs from the angle valve to the mast valve. Why is this? Why wouldn't it return to the tank? The mast valve already has a pressure line running to it.

What is the reasoning behind the 2 pumps running 2 separate lines to each of the valves?

How would I plumb this to run from one supply line?

How much pressure is on the line that comes out of the mast valve and goes to the filter? It can't be much, and where did the pressure go that was supplying the valve?

Sorry for so many questions, I'm soaking up as much as I can as fast as I can.

Thanks!

 

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OK, found more info that may help. It looks like on the mast valve, next to the fitting that runs to the angle valve, it has a CO cast into the mast valve. Could this be Carry Over, as in High Pressure Carry Over, as in power beyond? If this is the case, still, what's the deal with a pressure line coming from the mast valve to the angle valve, and then the other line to the angle valve running to a pump?

Hmm?

 

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Only a guess. Perhaps the small pump runs the tilt cyls. (low flow = better control) and the large pump the mast cyl. with the small pump adding flow for a faster lift.

ron

 

[Wayne County Hose]

I don't have much time right now, I'll answer more completely later.
Mast raise is a high pressure application, single acting cylinder. Tilt is a low pressure application. Probably also runs the steering circuit. Line from the tilt valve to the lift valve is for return to tank. When run together, takes less parts, therefore, less money.

 

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WCH, I eagerly await your response to the first questions

The lift valve has a tag that says it is a Parker VDP 11 P 34 (and at the end of that line is a hand stamped H) which according to the literature, says it's an open center, single acting spool with only B port used. The H means it has a power beyond sleeve.

It makes sense what you said about return from the angle valve, but would the lift valve have a power beyond sleeve in the return port?

Thanks for your help,
Mike

 

[Wayne County Hose]

WCH, I eagerly await your response to the first questions

The lift valve has a tag that says it is a Parker VDP 11 P 34 (and at the end of that line is a hand stamped H) which according to the literature, says it's an open center, single acting spool with only B port used. The H means it has a power beyond sleeve.

It makes sense what you said about return from the angle valve, but would the lift valve have a power beyond sleeve in the return port?

Thanks for your help,
Mike

I don't know what the Parker #'s mean, but I do know how they configured these valves. They only use one work port for lift, in your case, B port. This is because they only have one line running to the lift cylinder. It's a single acting cylinder, power up, gravity down. The A port gets capped. See next post.

 

[Wayne County Hose]

I'm trying to figure out how to pull some hydraulics off a dead forklift to use on my Kubota with rear remotes and was hoping I could get some help in understanding how it's plumbed. I've attached a sketch of how it's plumbed, for a visual.

The forklift has a valve that raises the mast, and another valve that angles the mast, both are Parker VDP valves. The angle valve looks to be like a normal DA cylinder valve. The mast valve is a little funky. Well, first, there is what looks to be 2 pumps running piggyback off the same shaft. A small pump and a big pump. The "out" of the small pump runs to the angle valve and the "out" of the big pump runs to the mast valve.

One thing I don't understand, is that a line runs from the angle valve to the mast valve. Why is this? Why wouldn't it return to the tank? The mast valve already has a pressure line running to it.

They do this to save costs on plumbing. If they all go back to tank anyway, the earlier they can do it, the less hose they use, the more money they save.

What is the reasoning behind the 2 pumps running 2 separate lines to each of the valves?

They run 2 different pressures, one high pressure for the mast lift, (about 2250 psi) one low pressure for mast tilt, steering, and any other hyd accessories. (about 1100 psi)

How would I plumb this to run from one supply line?

The same way you would plumb anything else.

How much pressure is on the line that comes out of the mast valve and goes to the filter? It can't be much, and where did the pressure go that was supplying the valve?

Between the mast lift valve and tank, there isn't much pressure. Where did the pressure go? It was reduced by flowing thru a larger line which has less restriction, therefore, lowering the working pressure. General rule of thumb, for hose sizes, is suction line is 2x the pressure line i.d. Return line is 1.5x the pressure line i.d.

Sorry for so many questions, I'm soaking up as much as I can as fast as I can.

Don't be afraid to ask, none of us were born experts.
Forklifts generally have very high quality hydraulic components. Anything you can use off a forklift should do the job for you.

 

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Great information!

The lift cylinder is single acting, but has a hose that comes out of the top of it, with nothing more than a hose clamp holding it on. Does anything come out of that and at what pressure? Can that hose be Tee'd into the return to the tractor or should it have its own direct return to tank separate from the valve returns, or atmospheric vent, or...?

So, for plumbing the valves, I'm thinking that pressure from the tractor should go to the lift valve first, make sure a PB sleeve is in there, then continue it from the PB port to the angle valve (my new TnT valve!) pressure port. Tee each of the valve's returns together, back to the tractor. Am I getting close?

 

[Wayne County Hose]

The lift cylinder is single acting, but has a hose that comes out of the top of it, with nothing more than a hose clamp holding it on. Does anything come out of that and at what pressure? Can that hose be Tee'd into the return to the tractor or should it have its own direct return to tank separate from the valve returns, or atmospheric vent, or...?[/QUOTE]


The hose coming out the top of the cylinder is a dump back to tank. It's there for 2 reasons.
1. To provide a vent for clean air. Being a single acting cylinder, when the cylinder extends and contracts, it pushes out and pulls in air. This hose goes to the tank and is pulling in air from the tank that already went thru a breather assembly.
2. When the cylinder seals leak, instead of spilling oil on the cylinder and floor, the hose carries the fluid back to tank.
A real easy way to see if this style cylinder is leaking is to put a load on it and disconnect the small hose from the tank. If there is fluid flow, the seals are leaking. This fluid flow would be the fluid bypassing the seals.
There should be very minimal pressure at most thru this line.
Do not Tee into this line or do anything else to it. Just let it do it's job.

So, for plumbing the valves, I'm thinking that pressure from the tractor should go to the lift valve first, make sure a PB sleeve is in there, then continue it from the PB port to the angle valve (my new TnT valve!) pressure port. Tee each of the valve's returns together, back to the tractor. Am I getting close?[/QUOTE]

Sounds like you are on the right track.

 

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Just wanted to say thanks for all your help. The forklift project was a success.