hydraulics for dump

Joel59 · May 7, 2012

I am building a single axle dump truck. I am having trouble with the hydraulics. I have an air operated chelsea pto with a parker p16 pump attached to it. Out back I have one single acting hydraulic cylinder with a 3/4" "in" port on the bottom, and a 3/4" port on the top (nearest the cylinder rod).
Now my pump is not an actual "dump pump". It doesn't have a built in valve. I have bought a new single spool 3 way open center prince valve. It is 20gpm.
I am trying to make this system work using the hydraulic cylinder as the reservoir. My cousin has the same size cylinder on his truck and uses it as the hydraulic tank/reservoir. However, his truck has a true "dump pump" on it so the valve is built into it. No matter how i hook mine up, the cylinder will not go up and down. Any suggestions or drawings of how I should be hooked with this type system? thanks.

mkirsch · May 7, 2012

Well first off are you sure the pump is any good?

Second off have you tried using an external reservoir?

I think you may have some fluid draw issues trying to use the cylinder as the only reservoir.

Your buddy's "dump pump" has a small internal reservoir that it draws from, and the cylinder is just an auxiliary reservoir to hold enough extra fluid to dump the bed.

I would hook it up like this:

1. Small 1-2 gallon hydraulic reservoir mounted near the pump.
2. Port near bottom of reservoir to suction side of pump.
3. Pressure side of pump to IN on 3-way valve.
4. OUT on 3-way valve back to port near top of reservoir.
5. Line from work port on 3-way valve to bottom port on cylinder.
6. Line from top of cylinder to fill port on small reservoir.

RodinNS · May 7, 2012

Sorry... but you need a resevoir. I don't know if your buddy has an old Edbro scope or a double acting type and a Williams tank/pump/valve combo... but either way he has a resevoir somewhere.
You probably don't need much more than a few gallons for a resevoir once you get the cylinder filled... but you need something.
Plumb the resevoir to the pump intake, pump outlet to control valve and valve return back to the tank. Then the two work lines of the valve to the respective ports on the cylinder. The tank you use will need to displace a volume equal to the volume of the cylinder rod plus some margin so the pump doesn't cavitate.
Hope you haven't destroyed your pump already...

Rod

Paul Janke · May 7, 2012

The line from the top of the cylinder is going to need to go below the fluid level in the reservoir in order to suck fluid into the cylinder while the dump is on its way down. Also, it is always good to go through a filter on the way back to the reservoir after exiting the valve.

greygoat · May 7, 2012

Unless you have a special cylinder, made for the
porpose, the "Rod end" of the cylinder doesn"t
have enough oil to fully raise the larger
displacement, "piston end" to it"s full stroke.
On almost anything but a special built hydraulic
valve, you"ll have 4 ports, an inlet, a return,
and 2 work ports. Oil goes to eather work port
depending on handle position. a "three way valve"
may have 1 work port blocked, or, not used, so
when the control handle goes 1 way, a cylinder
extends,when handle goes the other way, a cylinder retracts...that is..the weight of the
dump box push"s it down, but the oil returns to
te reservior, or tank, out of the return port.
how to get the oil to go back into the bottom,or
piston end of the cylinder, and let the pump
suck from that port also, is your problem, maybe
you need some check valves in the circuit.

Joel59 · May 7, 2012

The cylinder is approximately 36" long and 8" in diameter.
The pump is working. I put the suction line in a bucket of hydraulic oil and it drew it up as it should.
Funny thing is, the cylinder attempts to raise (slowly) when I release the clutch on the truck, and lower slightly as I press the clutch in. The valve has no effect on it, however I see from your advice that I am plumbed wrong (not using the "work" port. I had the pressure line going to the "in" side of the valve and the line going to the bottom of the cylinder coming from the "out" side of the valve.
Yes, according to the spec. sheet on the prince valve, the "b" work port is plugged.

Joel59 · May 7, 2012

Also, it won't be a problem to add a hydraulic tank. I have about an 8 gallon tank available. However, in all of the hydraulic schematics that I have seen they only show a cylinder with the bottom "in" port. They never show what to hook my top cylinder port to- (the one up by the chrome rod).

Joel59 · May 7, 2012

wouldn't this be for a double acting cylinder? or does a single acting cylinder suck fluid on the down stroke too?

Paul Janke · May 7, 2012

You said you had ports at both ends of the cylinder. That would probably make it a double acting cylinder.

mkirsch · May 7, 2012

The top port could be:

1. The down pressure port if it is a double acting cylinder.
2. Auxiliary reservoir.
3. A simple vent.

A double-acting cylinder can be treated as a single-acting, and be used in any of the three ways listed above.

Frankly, if you've got enough reservoir, I would simply install a vented plug in the top port and forget about it.

hydraulics for dump

Joel59

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mkirsch

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RodinNS

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Paul Janke

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greygoat

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Joel59

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Joel59

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Joel59

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Paul Janke

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mkirsch

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