Lock Valve (double piloted checkvalve) Plumbing

[Glenn9643]

I've ordered a lock valve for my tilt cylinder from Surplus Center
http://www.surpluscenter.com/item.asp?UID=2004021406364770&item=9-2903&catname=hydraulic
Anyone have any idea how difficult it is to plumb in? Is it a fairly simple job or would it require taking to a hydraulic shop?

 

[Inspector507]

I suppose you'd plumb it in like one of CCI's top links, hope he didn't mine me borrowing his pic /forums/images/graemlins/grin.gif.
But I see that check valve only has a crack pressure of 25 PSI and they have none in stock.
top link

 

[MadReferee]

You might want to take a look at this thread. I suggested that same valve and CCI and Jim Mc pointed out that it WILL NOT do the job correctly.

double pilot operated check valve

 

[Glenn9643]

They don't show any in stock because I bought the one they had yesterday. I'm not convinced yet that it won't work. 25 psi cracking pressure is what is required to open the valve when it's not under load. When under a load the pressure required to open the valve is determined by the pilot ratio, and from what I can tell at the Snap-Tite site all theirs are 4:1, meaning that under a 2000 psi load it would require 500 PSI to open the valve. I'm going to try it and if it doesn't work it won't be much lost. My question about plumbing it didn't refer to what goes where, but rather the cutting and flaring of the steel tubing and connections.

 

[Glenn9643]

I saw the same post and had questions about the required 500PSI cracking pressure. I've looked at web sites for several days and not seen a lock valve with a cracking pressure over 60 PSI, and that cast doubts on the 500 PSI theory to me. When I asked in that same thread I didn't receive an answer that explained it to my satisfaction, but maybe I'm hardheaded. I did find that the "cracking pressure" is the PSI required to open the valve without a load, and the "pilot ratio" of the lock valve determines the percentage of the load PSI required to open the valve. Seems to me that the working pressure of this valve is OK (3000PSI). It will require 25 PSI to open or close the cylinder when not under load. When I'm bushhogging it will require 25% of the load PSI to open the valve as the pilot ratio is 4:1. My question isn't whether it will work, but as to the difficulty of making the connections up with steel tubing.

 

[Henro]

Glen,

I don't think it is a question of whether this particular lock valve would work to lock a cylinder in place, but more a question of what is going to operate the pilot valves within the lock valve itself.

My take on this particular lock valve is that it requires a seperate pilot pressure source, as compared to other type lock valves which use the actual pressure that comes from the control valve that is used to operate the cylinder itself.

In otherwords, the lock valve that we see mounted on CCM's cylinders or on the TCC cylinders are the type that don't need an seperate pilot pressure applied. Those lock valves have four connecting points for hydraulic hoses. Two that come from the control valve and two that go from the lock valve to the cylinder being controlled.

So the question is does that lock valve you ordered from the Surplus Center have four or five places to hook hoses to? IF it only has four than it will probably work. If it has five [or maybe six] then it is designed to be used in a system that has a seperate source of hydraulic pressure to unlock lock valves...and it probably will not work, at least not without some creative plumbing on your part.

Like I said, this is my take on that valve without seeing any specs, drawings or physical representations of the internals of this lock valve.

Use to hold double acting cylinders in place until pilot pressure “unlocks” circuit. is what got me worried that this particular lock valve required a pilot pressure independent of the working pressure that is sent to the cylinder.

I hope I am wrong as I would like to buy a couple of these same lock valves if they would work the same as CCM's do.

Let us know how this turns out.

 

[HayDR]

THE #1 reason the check valve is used is to counter bleed by from the valve. We have checked thousands of tractors for bleed-by problems. I'd say 40% of them have some bleed-by when cold and it much higher % when the tractors are hot. If that bleed-by pressure exceeds 25 PSI on the said valve the cylinder will move. If you have a higher cracking pressure, 30-35 BAR, then the piloted check valve will not allow movement until the cracking pressure is eclipsed.

 

[Henro]

CCM,

That is an interesting point. I can see the point you are making about the bleed by problems.

I wish I was sure of the difference between cracking pressure and the ratio of pressure needed to operate lock valve pilot spools...I think these are different issues, but that is only an assumption on my part at this point in time.

I know on one particual prince valve the RD1400 has two check valves inside, and a pilot spool that opens the check valve on the side which finds oil flowing in the direction against the check valve. This valve has a pilot ration of 4 to 1. Which I assume means that it takes about 500 psi to operate the lock valve in a 2,000 psi system.

A check valve may be a ball held against a seat by a spring. The spring pressure would have to be overcome before the ball could be pushed away from the seat, and fluid would flow. To me the pressure required to lift the ball off the seat would be the cracking pressure.

But since the lock valve has two check valves hooked up in opposition, cracking pressure [if I am defining it right] is not an issue, because the same pressure that would cause one check valve to crack, would push the other check valve's ball tighter against the valve seat.

Now the important point is that because of the blead through you mentioned, if there is no check valve, it is likely the cylinder will be moving all the time, even when the control valve is centered, if the cylinder feels any force on it.

Now is this true for an open center valve, like are common on tractors?

Anyway, I guess what I am trying to say is that I wish someone would define cracking pressure and pilot ratio in terms we could all understand... /forums/images/graemlins/tongue.gif

 

[Henro]

Glen, that lock valve may be a winner...look here...

Glen, if that lock valve is the same one as the CAD series at the Snap Tite page above (about half way down) it looks like it is exactly what you want.

Let us know when you get it! If it is I will may soon have a couple on order myself! /forums/images/graemlins/smile.gif