04 06 56 hydraulic valve anatomy

karl f · Apr 29, 2017

What is the purpose of the reverse flow poppet valve? I have a guess and I know from experience that if the o-rings on 22 fail or the poppet doesn't seat the load will drop or creep.

Karl f

Poppet is number 20

P.s. My guess relates to cylinder cavitation

pete 23 · Apr 29, 2017

As name implies, prevents reverse flow to pump. Has nothing to do
with holding a load up. When you have several hundred psi holding a
load and pull a valve lever, the oil in loaded cylinder tries to
flow toward pump before pump has time to overcome pressure in
cylinder.

karl f · Apr 29, 2017

(quoted from post at 07:04:06 04/29/17) Has nothing to do
with holding a load up. .

I mentioned holding a load because
5-10 years ago I bought a used valve from an individual who said he went through it. Immediately I had an issue with it holding the load, instant drop. Told the seller about it and he said the only thing he didn't look at or replace was the o rings on the check valve so to look at that. I removed the poppet retainer (22) leaving the remote assembly installed on the tractor and sure enough the o rings on 22 were degraded with cracks and tears. Replaced them and it held the load.

Karl f

pete 23 · Apr 29, 2017

If you will look at the schematic of those valves you see that the holding pressure is exposed only to the spool and any leakage past the spool will take a path to tank, not back to the check valve.

Also, anti cavitation check valves are not exposed to pump, as they are connected between loaded cylinders and possibly tank.

04 06 56 hydraulic valve anatomy

karl f

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pete 23

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karl f

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pete 23

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