Hydraulic opinion

[J_J]

I have been discussing a hyd situation in the Power-Trac with Bob, who has mounted a hyd winch on the rear of his PT.

I have never seen a situation like this. Bob wants to control the winch from the rear with a single spool valve with PB. He is sending fluid from a front valve via the work ports to the rear valve input ports. . He is attempting to use either valve to control the winch by locking down the other lever.

The big question here is what will happen if the rear valve fluid flows in the reverse direction. Otherwise, in the normal flow of things, with hyd flow into the P port, and exiting the PB port .

If he then reverses the front valve, the fluid will now flow into the PB port and out the IN/P port.

Can you operate a hyd motor with an open center valve using reverse flow?

I think no, or just don't know

 

[Craig Clayton]

Lets try this steo by step.
Pump is supplying hydraulic oil to valve # 1 at inlet
Oil returns to sump from outlet of # 1 valve.
Pressure adjustment is at #1 valve to sump
There is a pair of open center lines to #2 valve inlet and return
Oil returns to # 1 work port through pair of open center lines from # 2 valve
Valve # 2 has a pair of open center work port lines to a hydraulic motor
Hydraulic motor turns input shaft of winch.


So far so good

Aslong as # 1 spool is only moved in the correct direction it should work.
It sounds very similiar as to how I am powering my BH at the moment. I use a soft strap so I only can PULL on the spool valve #1 and I tie the strap arond the ROPS with a slip knot.
Craig Clayton

 

[J_J]

Question is , what will happen if the flow is reversed using the front valve.

Will the winch motor work normally or not at all in reverse flow?

Any fluid used by the hyd motor should exit out the tank gallery on the second valve.

 

[RickB]

Question is , what will happen if the flow is reversed using the front valve.

Will the winch motor work normally or not at all in reverse flow?

Any fluid used by the hyd motor should exit out the tank gallery on the second valve.

I believe it will work as intended. When the second valve is powered through the PB port (reverse flow), the return oil from the winch motor may flow back to valve #1 from the P port of #2 valve and to sump by whatever means that #1 valve returns to tank.

 

[J_J]

I thought the gallery's for the work ports only went to the out or return ports. Is that not correct?

 

[Craig Clayton]

The only problem with applying the first valve in the reverse flow is the gallery will be
have pressure on it when it is not intended to.
The reason I pull my spool by the soft cord is I call my line as a Positive Flow and I know the direction of the oil. This oil goes to the inlet of the BH which is like where it should be.
Craig Clayton

 

[AKKAMAAN]

I thought the gallery's for the work ports only went to the out or return ports. Is that not correct?

agree w RickB...

How would pump connect to cylinder/motor if not through work port??

EDIT:
A load check valve in valve #1, would cause flow pro blems in reverse

 

[RickB]

I thought the gallery's for the work ports only went to the out or return ports. Is that not correct?

That's correct, but with the flow coming IN to valve #2 PB port in that instance, I'm not certain where the flow would go.

The more that I think about this, I'm pretty certain that with valve spool #2 centered in neutral, flow INTO the PB port of valve #2 would exit the P port of that valve.
Also, with the valve spool of valve #2 stroked, the flow entering the PB port of that valve would either go directly to tank via the return port
(edit; that's not going to happen, see my next post),

or be deadheaded by the valve spool. No flow into valve #2 entering via the PB port would pass around the spool and exit the work port of valve #2 to power the winch.

The issue of reverse flow into a PB valve is more of what happens to the pressure flow, not where the return flow ends up. I don't think the intended work will be accomplished, and a simple air test with a rubber-tipped blowgun would answer the riddle without plumbing or mess.

 

[RickB]

I thought the gallery's for the work ports only went to the out or return ports. Is that not correct?

The more I think about this, the more certain I am that flow coming into #2 valve's PB port will be deadheaded when the #2 spool is stroked. Two ways for Bob to accomplish what he wants with components already discussed:
1. Remove the PB sleeve from valve #2 and let return and PB ports be common.
2. Connect the lines from the work ports of valve #1 to P and Return ports of valve #2, plugging the PB port.

Both alternatives are flawed in that when the winch creates a high load and flow into the PB/return side of valve #2 approaches RVF pressure, the spool seals of valve #2 will become compromised, sonoer or later.

Best solution with common hydraulic components is to mount the two valves in parallel and feed either one or the other via a selector valve, either manual or electric.

 

[J_J]

agree w RickB...

How would pump connect to cylinder/motor if not through work port??

EDIT:
A load check valve in valve #1, would cause flow pro blems in reverse

What I meant to say was that the work ports used fluid from a cyl or motor dumps into the OUT/TANK port. So if you pressurize the out port as in a reverse condition, you stand a good chance of damage to the valve since the psi on the out port is about 500 psi. If the winch motor loads up, you will far exceed that pressure.