Unloading Problem

Hi everyone, Got a problem with one of are frick boosters unloading I am suspecting a bad glide seal. So here's what i got. On quantum panels in calibration screen if i try and unload the slide stop it takes forever like 15 minutes to move from 5.0 to 2.2 if i move the slide valve at all this loads up the slide stop even if i have it have the slide stop on unload. Replaced the slide stop potentiometer and replaced the Yuken valve just to rule these out. I valved off the slide stop Yuken valve still moves the slide stop when i move the slide valve? Any other recommendations?

Coil is OK ?

Put on brand new one for the slide stop. Talking about hydraulic proportioning valve right?

I know very little about Frick but , would run slide stop + slide valve up / down to make sure hydraulic cylinder is primed with oil .
If you then can isolate slide stop cylinder if above makes no difference .
If isolated and primed with oil it should not move unless seals internally or on suction side of cylinder are leaking .
Manually load + unload slide valve to see what happens .

Yep tried that already. Slide stop still moves.

Leaking seals then ?
Time for unloader end overhaul .
How many hrs since last overhaul , any idea ?

only about 35k hours. But wouldnt surprise me i am just learning the quantum controllers and they had them set to load and unload every .5 lb above or below setpoint so they where always hunting. Was a new block about 4 years ago and this particular booster runs 98% of the time. I already had to replace the slide stop and slide valve indicating rods because they where wore out.

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Originally Posted by Poodzy

only about 35k hours. But wouldnt surprise me i am just learning the quantum controllers and they had them set to load and unload every .5 lb above or below setpoint so they where always hunting. Was a new block about 4 years ago and this particular booster runs 98% of the time. I already had to replace the slide stop and slide valve indicating rods because they where wore out.

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To reduce hunting, you can increase dead band from 1 psig to 2 psig. You can slow down the slide by throttling the solenoid valves.

ok tell me how you calibrated the slide valve and slide stop. you are suposed to calibrate the slide stop first and then the slide valve. as far as the hunting keep your dead band at .5 psig and riase your proportional band. the porportional band is relative to your setpoint.

i cannot calibrate this particular machine. the slide stop will not unload. I have to have the machine off to unload it with just the oil pump. If the machine is running it will not go down all the way. Thanks though even with the machine off it still takes a very long time. Thanks for the response though. I raised are dead band to .8 lbs and seems to work allot better.

Im confused, raising the dead band should make a difference manually unloading / loading the slide stop. Will the slide valve load and unload? What kind of pressures are you working with?

The main problem that i have is when the slide valve moves, the slide stop is also moving so any time the machine is loaded or unloaded the slide stop loads up, we have come to the conclusion that the unloading seal on the slide stop is bad and needs to be replaced. Even manually pushing the hydraulic valves in it will not unload. Only way to get slide stop unloaded is to have the machine off. So changing the proportional and dead band will do nothing really. Pressure are 1st stg 7hg, 2nd stg 25lbs, head pressure 140 lbs.

Hard to understand why slide stop moves with main slide valve . Does it do it in both load and unload ?

If you pumped down compressor could you use compressed air or nitrogen to pressure both sides of slide stop and main slide valve pistons to narrow which seals are leaking internally .

Use a stop valve with gauge downstream on each position tested while other ports are open to atmoshere .
See where it comes out
With that big mother spring holding slide stop and slidevalve apart i can only suggest you manually prime both cylinders on both sides if above pressue test does'nt find anything obvious .

Also slide stop i thought would always stay on 2.2 - 3.6 Vi if its a booster .

Does it require more oil pressure to make load/unload ?

Had another thought aout this and think it would be worth checking directional control valve piping ( yucon )on slide stop .
Is there a chance its piped up incorrectly as its worth eliminating before any major work .
Have seen this on e few jobs over the years as pipes could go in a few positions if your not careful .

A + B ports are for cylinder P for oil pressure and T for oil return back into suction , if its same as what we deal with anyway . Connections cast on back of mounting block .

Quote:

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Originally Posted by RANGER1

Hard to understand why slide stop moves with main slide valve . Does it do it in both load and unload ?

If you pumped down compressor could you use compressed air or nitrogen to pressure both sides of slide stop and main slide valve pistons to narrow which seals are leaking internally .

Use a stop valve with gauge downstream on each position tested while other ports are open to atmoshere .
See where it comes out
With that big mother spring holding slide stop and slidevalve apart i can only suggest you manually prime both cylinders on both sides if above pressue test does'nt find anything obvious .

Also slide stop i thought would always stay on 2.2 - 3.6 Vi if its a booster .

Does it require more oil pressure to make load/unload ?

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As far as running yes the booster very rarely gets above 3.0.. I will try and prime the valve next week not sure how they would bleed down to nothing when running though. It orignally kicked out on failure to unload. the piping for the slide stop has been there for many years so i am betting it is correct. I will try and pressurize the pistion later today very good idea thanks for sharing.

Thanks for all the replys to this issue but the problem has been identified and its a really stupid design flaw is all it is, I finally got to work on it the last couple of days and figured out that the reason it wont unload correctly is they both (slide valve,stop) share the same high pressure line and releif line. So due to pressure differental when we have big pressure swings and the slide valve and slide stop unload at the same time the slide valve is pushing oil into the slide stop chamber. Bad design.