Lets talk leakdown

[woodlandfarms]

So following coolconnections thread, I was wondering how long it takes for everyones PT to leakdown. I have felt mine was rather quick, but the more I hear it sounds like the norm.

So say you raise up your mower deck, turn off the engine and walk away. For me it is about 20 minutes to a half hour before it hits the ground. Granted the mower is a heavy implement and my tractor has anemic lift.

 

[cqaigy2]

Probably about 10-15 for the brush mower.

 

[ponytug]

Carl,
While you didn't give a height, that sounds about right, although I make it a practice to relieve the pressure in the hydraulic system after the engine is off.

I once asked Terry about it. He said they chose to have a valve control with a pin hole bypass to tank to prevent overpressure in the systems due to temperature changes when the tractor was parked. The tradeoff is the slow leakdown.

Mostly, I don't notice it, unless I need to have the bucket or forks in some position for loading/unloading, when the leakdown can cause the load to be in a less than desirable location after some amount of time.

All the best,

Peter

 

[woodlandfarms]

So as we move forward, or course I keep the arms and implements down when not running. BUT I do break the rules and climb under the mower only supported by the arms when trying to remove a broken bolt or bang a mower blade free. Stupid Dangerous and I am fully aware of what I am doing.

But the drift happens when I have a full bucket of dirt and have to go from one side of the property to the other, or am spraying (the sprayer mounts on the front of the tractor). Drift is a real PITA then.

Pony thanks for the notes on the pin hole bypass. Makes sense. Actually, it doesn't make sense as I dont think other tractors do this. Even Bobcats (skip loaders) don't leak down like the PT does. But glad it isn't just me.

 

[J_J]

My lift arms will stay up for about 12 hrs.

You guys should know the reason for leak down, and whether you want to live with it as is.

It is either worn seals or the valve spool .

I have never heard of a dedicated leak down on purpose.

If you want to test the cyl, add a needle valve to the base end of the cyl.

Then raise the lift arms and turn the needle valve closed.

Shut engine off.

If leak down occurs, then you know the weight of the arms is forcing the fluid to bypass.

If that is what is happening, order the cyl rebuild kits, and rebuild.

 

[ponytug]

I'm only passing on what Terry said. He said it was either this, or dedicated pressure relief valves in each circuit.

Given the PT tendency to choose cheap and simple over costly and complex, I can see where they are coming from. Personally, I'm too cheap to redo the circuits.

Of course, I may have misunderstood what he was saying.

All the best,

Peter

My lift arms will stay up for about 12 hrs.

You guys should know the reason for leak down, and whether you want to live with it as is.

It is either worn seals or the valve spool .

I have never heard of a dedicated leak down on purpose.

If you want to test the cyl, add a needle valve to the base end of the cyl.

Then raise the lift arms and turn the needle valve closed.

Shut engine off.

If leak down occurs, then you know the weight of the arms is forcing the fluid to bypass.

If that is what is happening, order the cyl rebuild kits, and rebuild.

 

[woodlandfarms]

Now one thing comes to mind... If I let the arms leak down it effects the seat circuit. The seat will tip to the right, pressure going to the levelingg piston. So something is leaking by something

 

[MossRoad]

My lift arms will stay up for about 12 hrs.

You guys should know the reason for leak down, and whether you want to live with it as is.

It is either worn seals or the valve spool .

I have never heard of a dedicated leak down on purpose.

If you want to test the cyl, add a needle valve to the base end of the cyl.

Then raise the lift arms and turn the needle valve closed.

Shut engine off.

If leak down occurs, then you know the weight of the arms is forcing the fluid to bypass.

If that is what is happening, order the cyl rebuild kits, and rebuild.

J_J,
The problem of leak down of the FEL arms when the tractor is off occurs on all the models of PT directly from the factory that I know of. I think its their choice of valves or cylinders that causes it (cheap), not anything that is leaking from wear and tear. Yours is of course, an earlier model and may not be affected by that.

 

[J_J]

I just don't believe anyone would pick a valve for the leak sown rate.

I think they got a good deal on the valves they used, and I would also think they would have changed valve manufacturer over time.

The valves must be pretty descent as I have not heard of anyone replacing theirs.

I thought my valve was leaking awhile back, so I removed it and took it to a hyd shop and they put it on the hyd bench and ran a relief test, and work port test.

The result was no problem.

Cost for the test on the three spool valve, about $40.

Prince says 10 cc per min is max for valve leakage.

10 cc = .338 fl oz

1 hr = 20.28 oz

6 hr = 121.28 oz, or .95 gal

12 hr = 243.36 oz , or 1.9 gal

So, if the lift cyl were bypassing at that rate, you might expect the arms to fall over time.

 

[SpringHollow]

Hi JJ,

I heard the same thing from Terry and I have mentioned it here before. I have needle valves in line and if i lock those down, the lift arms stay.

I am not sure how other manufacturers deal with pressure relief when the circuits are closed. I suspect they just do not worry about it.

Ken

 

[SpringHollow]

All of our attachments are sealed when we remove them with no pressure relief.

Ken

 

[J_J]

Hi JJ,

I heard the same thing from Terry and I have mentioned it here before. I have needle valves in line and if i lock those down, the lift arms stay.

I am not sure how other manufacturers deal with pressure relief when the circuits are closed. I suspect they just do not worry about it.

Ken

You have proved that your cyl are good

I believe you have answered your questions, and it is that your valve spools are leaking.

How much can you tolerate is what you have to answer.

You can't rebuild them, so a new valve should be in your thoughts, but only if you are worried about the lift arms falling.

Of course, if they are falling, they are leaking when you are trying to lift a load.

You can judge the leakage by looking at a hyd gage when you are lifting a large load and see if it can maintain a high pressure and not go into relief.

 

[SpringHollow]

Carl,

A couple of years ago on my PT, i would catastrophically lose lift on my loader arms and would drop the load. It ended up being the steering cylinders that needed the rebuild. They got so bad that I could not steer. When I fixed them, then the catastrophic problem with the loader went away. Life is not nearly as exciting now that I no longer have to guess when my loader will fall down.

Ken

 

[cqaigy2]

your valve spools are leaking.

I have to admit that is what i assumed the leak down was from.

 

[SpringHollow]

Again, per Terry, the valve they chose slowly leaks.

Ken

 

[J_J]

In general, you can say that about anything hyd.

However there is an acceptable leak down rate that they use to replace valves and cyl when new.

Prince engineers use 10 cc per min.

 

[ponytug]

Given the size of the cylinders, 10 cc/min would be in the range.

I can tell you that it is a higher rate if there is crud under the check valve.

All the best,

Peter

In general, you can say that about anything hyd.

However there is an acceptable leak down rate that they use to replace valves and cyl when new.

Prince engineers use 10 cc per min.

 

[woodlandfarms]

Can someone give me instructions on how to clean out my control? From a standpoint of a novice? I have no clue what a check valve us.

 

[J_J]

If you are talking about load checks, they are usually located between the work ports.

The purpose of the load checks is to prevent the cyl dropping as you shift the lever, and also to prevent fluid from flowing back into the input.

This valve from Prince is an example what a load check might look like.

http://www.princehyd.com/Portals/0/valves/LvtInstS.pdf

 

[headfirecracker]

My backhoe will leakdown sometimes within 5 to 7 sec while im trying to dig. I have checked ghe load checks and look to be good. Where do I need to loon now? I have noticed that if I put down pressure on boom and then raise it back up it will stay sometimes. Now im noticing the front bucket is trying to bypass it has more lifting power than other times I can try and lift something and say the third time itru it will lift.