Valve leak down

[marrt]

Has anyone thought about replacing the PT valve assembly with an alternative? Frankly, I don’t like the leak down “benefit” (I’m always careful to lower the bucket when I shut the tractor off at days end). I understand it’s dangerous to leave a bucket etc. up with the tractor off. However, sometimes, this is useful even if it increases the safety risk. When changing mower blades for example. However, if I raise the 770 lbs 1845 mower with the hydraulic oil hot, it will leak down in a matter of minutes. My 425 did the same thing.

 

[J_J]

There are load checks that you can add to your system. Yes, you can replace those valves with newer type valves that have built in load checks. If I remember right, the external load checks are pilot operated, which means that they will hold a cylinder in the last position until you operate the pilot which releases the check. Simlar to the one below. You guys correct me if I am wrong. I don't mind at all.

Don't bother to look at the valve, they removed it from their web site. Sorry. They still have some other models on their site.

http://www.surpluscenter.com/item.asp?UID=2006061516574641&item=9-1343&catname=hydraulic

 

[J_J]

Even the load or lock valves will not stop a cylinder from trying to equalize internally. If the seals are leaking, and you have a load, the load may force the hydraulic fluid to the other side of the piston, and the load may fall.

In contrast,
Someone last year said that they had blew the end off their cylinder. That almost had to be excessive pressure, or the linkage applied enough torque to pop it out.

 

[marrt]

Some of the load check valves say they are pilot operated. What does that mean?

 

[J_J]

Some of the load check valves say they are pilot operated. What does that mean?

Pilot operated means that another source of fluid is necessary to operate the pilot valve. For instance, if you had a check valve that was pilot operated, the check valve would not allow fluid to flow. So when you apply fluid to the pilot orfice, you release the valve and fluid is allowed to flow. Another way to express a pilot valve, is to think of a ball bearing sitting in a seat with a spring holding the valve closed. When you apply pressureized fluid, to the pilot, you push the ball off the seat and the fluid can flow freely.

If anybody else has a better explanation, just chime right in.

 

[Spiffy]

Since the PT is my first experience with "loose" valves, I've never had to use checks; however, I think they would be a very nice added layer of safety in the example of working on a mower or mine of painting the barn.

I've occasionally wondered if you can "feel" the split second while it releases. I was thinking about that again during some BH work the other day, if so, it'd be a definite negative for BH where often operating several spools at different rates; however, when actually thinking about it, I realized I really hate the leak down for BH work.

 

[marrt]

JJ, do you know if you can use the pressure from the lift circuit to also release the valve simultaneously? I thought some of the valve worked that way. For example, let’s assume you have a one way pilot check valve on the bottom of your lift cylinders to keep the bucket from leaking down (assuming you cylinder seals are good of course). You would add a T fitting to the top of the cylinder and run a hose down to the pilot of the valve. When you move the bucket down, you also apply pressure simultaneously to the pilot of the check valve, releasing the valve. Anyone know it they work this way?

 

[J_J]

Marrt, Fluid from any pressureized source would operate the check, because you are simply trying to raise the ball off the check.

 

[Spiffy]

Marrt, Fluid from any pressureized source would operate the check, because you are simply trying to raise the ball off the check.

I'm guessing for leakdown on the main lift, you'd only mostly be interested in "checking" the "pressure up" direction so would be able to do it with a single check. Else, I'm thinking that both lines would need to be T'ed to the cooresponding pilot so pressure existed.

At least that seems to be logical as I type this; "what say the experts?" [still getting used to the smilies now; I'm more inquiring than unhappily confused .... not sure the pink tonque one quite espresses my whimsical "confusion" with the confused smilie ]