Hydraulic issues

[tregear85]

Hi all, I have a power major that has a single hydraulic spool valve. I have operated a forklift successfully on this for a while. With the valve closed the link arms operate with the valve open the link arms would drop and the rise and fall would operate. However I have just purchased a permiter post knocker and it is not behaving! With the valve open it does not lift the weight instead it still lifts the link arms, I’m guessing the load required to activate the weight lift exceeds that required to lift the link arms. Presumably there is a hydraulic mod that can be done to completely isolate the spool valve from the link arms? Any advise gratefully received.

[oehrick]

Once the TPL arms have lifted up, the knocker cylinder should follow, unless your pump or PRV are leaking pressure badly or oil flow to the knocker is restricted, first thing is to check that with a gauge on the trailer pipe connector, which I presume is where you are taking your oil from, also worth checking the self sealing valves in both sides of the connector as these can inhibit flow if incorrectly set or spring damaged.

When you lift the arms and they reach the top you should hear a louder noise which is the PRV dumping excess oil until you release the lift lever, do you get this with the knocker connected or not ?

Is the knocker single acting ? = cylinder lifts a weight then drops it as the lift lever is lowered ? if not the oil in the other end of a double acting cylinder has no where to go and you'd need to fit a separate valve block and exhaust oil route (usually though a connector fitted to the rear end oil filler)

Second lift valve slices are sometimes about, the choice is buy one or just buy a Doe triple D instead

Come back with your findings, don't think I've seen a PM with a DAR valve which selects lift arm or trailer pipe operation on the Supers.

[tregear85]

When the arms get to the top they try to lift the knocker weight but fail so maybe there is a leaky seal. So when I purchased the tractor with the forks it had two bottle screws locking the TPL arms down I guess this is why! So I can get NDT all them for the knocker and check with a gauge do you know what pressure I should be looking for?
I will check the noise changes tonight. Yes I am running if the trailer pipe, the knocker is single acting.
I’ll come back to you with results shortly,
Thanks
Tim

[oehrick]

When you think of a Major heaving up a five ton load on a tipping trailer they were not fast but they got there, make no sense to not lift the weight, sounds to me as if you have a pressure loss or serious restriction somewhere.

Cr@p in the inlet filter to pump starving oil

Pump / seals worn

Oring on delivery pipe to top cover ditto

TPL lift arm cylinder seals / wear / damage

PRV damaged / sticking / contaminated

Are the likely candidates off the top of my head.

Have you a plough or something heavy for the lift arms to see if it still lifts them with a load and if they droop over a short period of time ?

2-2200 PSI is the un adjusted PRV pump output spec from the manual, a bit of hose from the trailer pipe would give an indication of flow if dumped back in through the filler.

HTH, it is a fairly simple system but they can still find infuriating problems !