Double Pilot Operated Check Valves

[Hugo Habicht]

Hello,

what an expression. I have to repeat it: "Double Pilot Operated Check Valves".

I have a rough idea what they do, how they operate but not really why they are needed. I do not want to mess up other threads where people have specific questions, so that's why I openend a new thread.

As far as I understand (correct me if I am wrong) those valves lock in the oil in a cylinder unless pressure is applied from A or B port.

If this is the case, why are they needed? Are the control valves too leaky for longer operation? If so, those valves are required on a three point hitch lift or tilt function, correct? Where else would they be required?

I also saw a video of somebody building a nice backhoe for his tractor and he had to add joysticks with those check valves built in. I think the boom was dropping while he moved the bucket arm, but here I really did not grasp why such a valve would be required in the joystick. He added them on the cylinders first, but that did not seem to work.

Any hints or links to good (!) websites explaining the usage of those valves would be apprecited.

Kind regards,
Hugo

 

[TheOldHokie]

Hello,

what an expression. I have to repeat it: "Double Pilot Operated Check Valves".

I have a rough idea what they do, how they operate but not really why they are needed. I do not want to mess up other threads where people have specific questions, so that's why I openend a new thread.

As far as I understand (correct me if I am wrong) those valves lock in the oil in a cylinder unless pressure is applied from A or B port.

If this is the case, why are they needed? Are the control valves too leaky for longer operation? If so, those valves are required on a three point hitch lift or tilt function, correct? Where else would they be required?

I also saw a video of somebody building a nice backhoe for his tractor and he had to add joysticks with those check valves built in. I think the boom was dropping while he moved the bucket arm, but here I really did not grasp why such a valve would be required in the joystick. He added them on the cylinders first, but that did not seem to work.

Any hints or links to good (!) websites explaining the usage of those valves would be apprecited.

Kind regards,
Hugo

1. A DPOCV has two opposed poppet type check valves that hydraulucally lock a double acting cylinder.
2. When acyusting pressure is applied to one port it opens the check vslve on that side allowung flow into the cylinder and an internal (mechanical) pilot opens the opposing check valve unlocking the culinder and allowing outflow.
3. Spool type directional controI valves all have some amount of internal spool leakage which allows a loaded cylinder to drift.
4. Poppet type pilot operated check valves are posituve shutoff devices and are used in conjunction with spool type control valves to prevent cylinder drift.

Dan

 

[PoTreeBoy]

Just to add a point to Dan's explanation.

You might wonder why all valves don't have this feature. Briefly, jerkiness. The pressure is held in the pressurized line until pressure building in the other line releases the ball/poppet/shuttle. Then the pressure is equalized suddenly. My backhoe stabilizers are the only circuits with DPOCV's. The last time I used it I had the tractor higher off the ground than normal. When I started to raise the stabilizers, the right one released dropping the right side of the tractor, throwing the FOP against my head. Fortunately my head is apparently as hard as I've always been told it is. This behavior would make fine control impossible.

 

[NCL4701]

Also, you can’t float a cylinder with DPOCVs.

My L has three rear remotes, one of which has a float detent. For some grading operations, the option to float the side link is helpful. For bush hogging areas with very rough topography, the option to float the toplink is helpful. Can’t float both at the same time because I only have the one float valve but can do either/or by swapping lines.

The spool valves do leak some, as Dan’s point #3 states. If I’m bush hogging, the side link will sag over time. DPOCVs would fix that but then I couldn’t float it to follow the contour of the grade for finish grading with box blade and back blade. I have the manual adjustable link on the other side and have it set such that full up on the hydraulic link is level, so every once in a while I reach down beside my right hip and bump it up whether it needs it or not when bush hogging. For something such as the skidding winch where precise level isn’t important it might sag enough to be worth bumping it back to level after enough time, but usually not.

Suspect DPOCV or not boils down to need for fine control and/or float v need to hold position rock solid until operator directs movement.

 

[TheOldHokie]

With the Summit P80 valves I have on my tractor the hydraulic top link drift was so bad it was basically unusable. They do not have float so an inline Summit DPOCV was a no brainer. The top link is now rock solid and even with a 700 pound Woods mower hanging way back I have no control problems and chatter is minimal.

YMMV,

Dan

 

[WI_Hedgehog]

On a small DPOV (5 GPM, 5,000#) 63lbs of hydraulic force is needed to overcome the poppet spring. I would guess that value varies depending on flow rate and pressure rating.

If a company doesn't list many specs I suspect it's an Asian clone of a higher quality part. I wonder if that's why Dan's P80 valves drift so much, low tolerances. My Kubota valves hold load front/rear for hours without drift, it'll be interesting to see what LandPride valves do (I believe they're high-quality Asian-made).

BUT, I'm new at this, so please correct this if I'm mistaken.

 

[TheOldHokie]

On a small DPOV (5 GPM, 5,000#) 63lbs of hydraulic force is needed to overcome the poppet spring. I would guess that value varies depending on flow rate and pressure rating.

If a company doesn't list many specs I suspect it's an Asian clone of a higher quality part. I wonder if that's why Dan's P80 valves drift so much, low tolerances. My Kubota valves hold load front/rear for hours without drift, it'll be interesting to see what LandPride valves do (I believe they're high-quality Asian-made).

BUT, I'm new at this, so please correct this if I'm mistaken.

I think you are looking for a scape goat.

The P80 on my tractor is made in Bulgaria by Badestnost, a well known European OEM. Their catalog description is quite extensve and detailed

https://hydraulic-vlv.com/files/mf/products/16_file.pdf

Spool leakage is claimed to be 6 cc/min @ 100 BAR and 46 cSt viscosity which is typical of numbers quoted by Prince, Husco, or Cross

I have no experience with Kubota OEM rear remotes but Kubota provodes no perfirmance specifications and a well known vendor here is quite vocal about them leaking.

I do jnow I can watch the LA525 loader drift notIceably when holding that sort of load. I have measured work port pressure and watched it bleed down from 2400 PSI to zero in about a minute. It drops to a few hundred PSI in just the fIrst few seconds.

My point is regardless of brand all of these control valves leak internally. High cylinder loads, very thin oil (SUDT2), and specific lift geometries can make it very noticeable/problematic.

Dan

 

[WI_Hedgehog]

I think you are looking for a scape goat.

The P80 on my tractor is made in Bulgaria by Badestnost, a well known European OEM. Their catalog description is quite extensve and detailed

https://hydraulic-vlv.com/files/mf/products/16_file.pdf

Spool leakage is claimed to be 6 cc/min @ 100 BAR and 46 cSt viscosity which is typical of numbers quoted by Prince, Husco, or Cross

I have no experience with Kubota OEM rear remotes but Kubota provodes no perfirmance specifications and a well known vendor here is quite vocal about them leaking.

I do jnow I can watch the LA525 loader drift notIceably when holding that sort of load. I have measured work port pressure and watched it bleed down from 2400 PSI to zero in about a minute. It drops to a few hundred PSI in just the fIrst few seconds.

My point is regardless of brand all of these control valves leak internally. High cylinder loads, very thin oil (SUDT2), and specific lift geometries can make it very noticeable/problematic.

Dan

That's an incredible amount of spool leakage to someone who's new to all this, I wouldn't have guessed. Seems I have gotten excellent valves so far and have a lot to learn!

 

[NCL4701]

My rear remotes are dealer installed OEM. I have no information on their specs, published leakage considered within normal limits, identity of manufacturer, or any other technical data.

When I put in the order with the salesman at my dealer, one of their requirements was I talk to the service manager. The whole point of that requirement was he made it clear that they leak. Their recommendation was DPOCVs on the top/tilt cylinders (which was also part of the scope of work) and if insisted on a float valve and no DPOCV’s I was verbally waiving my right to bitch at them about valve leakage unless oil was pouring out on the ground.

My rear remotes leak more than the FEL valve by a good bit. The FEL, if I park the tractor with the bucket 1” off the floor, it will be about 1” off the floor 24 hours later. A week later it will probably be on the floor. For practical purposes of operation, the loader valve has no appreciable leakage. Maybe a unicorn; don’t know. The top/tilt cylinders: if I’m using a rear blade, I’m moving them at least occasionally during the work and the leakage isn’t severe enough to be noticeable under those conditions. Something that’s a “set and forget” type implement, such as skidding winch or bush hog, requires tweaking every 45 minutes to an hour. IMO that’s not ideal, but it’s also not impractical.

When I had the dealer install the remotes, I had figured if the leakage was severe enough to cause practical operational problems I would have to add DOPCVs to the two center return remotes with a setup like @TheOldHokie linked in one of his posts above as that would allow use of the check valves when hooked to the center return remotes and ability to float by moving the appropriate cylinder’s lines to the float detent remote. I tried discussing that setup with the service manager at time of order but their only option was DPOCVs on the cylinders. So far, it hasn’t been a practical operational issue worthy of any time or money in my case. YMMV.

 

[Hugo Habicht]

That is interesting. I had assumed (incorrectly) that rear remotes, being open/closed valves would be practically leak free.

 

[TheOldHokie]

That is interesting. I had assumed (incorrectly) that rear remotes, being open/closed valves would be practically leak free.

Spool type directional control valves do not have "seals" and rely on the close sliding clearance between spool and valve body for the fluid seal. That is never leak tight and only gets worse with usage. You also need to remember there is a difference between pressure tight and fluid tight. You can leak pressure without leaking fluid. Here is a video showing pressure bleed off on a deadheaded work port. Port pessure plummets the instant the spool is returned to neutral even though there is no real fluid leakage. Thats why a grapple doesnt maintain its gripping force.

Dan

 

[WI_Hedgehog]

....Port pessure plummets the instant the spool is returned to neutral even though there is no real fluid leakage. Thats why a grapple doesnt maintain its gripping force.

Assuming I can get the grapple plumbed up within a few weeks with the parts ordered this morning, from what you said it looks like I'll likely have to add a check valve. Would I want to use a Single Pilot Operated Check Valve on the root rake grapple?

 

[TheOldHokie]

Assuming I can get the grapple plumbed up within a few weeks with the parts ordered this morning, from what you said it looks like I'll likely have to add a check valve. Would I want to use a Single Pilot Operated Check Valve on the root rake grapple?

Matter of personsl preference and how you intend to instsll it I think.

 

[PoTreeBoy]

Assuming I can get the grapple plumbed up within a few weeks with the parts ordered this morning, from what you said it looks like I'll likely have to add a check valve. Would I want to use a Single Pilot Operated Check Valve on the root rake grapple?

This thread has kind of forked. What have you ordered for your grapple/third function? Most folks install a solenoid valve which is a different animal from the spool valves the check valve discussion started with. I don't have personal experience with solenoid valves yet but I don't think they exhibit the leakage issue.

If you are installing a spool valve for your grapple, I wouldn't install a check valve unless experience shows you need it. I installed a third spool section on my loader valve for the third function. My grapple will loosen its grip a little over a few minutes if I'm hauling a load, but I just hit the lever to tighten it back up. It's no different from lifting the bucket back as it settles while roading the tractor.

 

[TheOldHokie]

This thread has kind of forked. What have you ordered for your grapple/third function? Most folks install a solenoid valve which is a different animal from the spool valves the check valve discussion started with. I don't have personal experience with solenoid valves yet but I don't think they exhibit the leakage issue.

If you are installing a spool valve for your grapple, I wouldn't install a check valve unless experience shows you need it. I installed a third spool section on my loader valve for the third function. My grapple will loosen its grip a little over a few minutes if I'm hauling a load, but I just hit the lever to tighten it back up. It's no different from lifting the bucket back as it settles while roading the tractor.

The "standard" for 3rd function is a D03 (CETOP 3/ NG6) industrial valve. They are spool type directional control valves with electromagnetic spool positioners.

Dan

 

[PoTreeBoy]

The "standard" for 3rd function is a D03 (CETOP 3/ NG6) industrial valve. They are spool type directional control valves with electromagnetic spool positioners.

Dan

So, same leakage issue?

 

[TheOldHokie]

So, same leakage issue?

In theory. I dont but have any catalog data for comparison but there will be some leakage.

Dan

 

[WI_Hedgehog]

This thread has kind of forked. What have you ordered for your grapple/third function? Most folks install a solenoid valve which is a different animal from the spool valves the check valve discussion started with. I don't have personal experience with solenoid valves yet but I don't think they exhibit the leakage issue.

I didn't mean to hijack the thread...

I have a LandPride Third Function Kit for a BX, so electronically it's "stagnant" or "all-out" in one of two directions, though it's a BX so "all-out" is more "sloth power" than "cheetah fast."

 

[TheOldHokie]

I didn't mean to hijack the thread...

I have a LandPride Third Function Kit for a BX, so electronically it's "stagnant" or "all-out" in one of two directions, though it's a BX so "all-out" is more "sloth power" than "cheetah fast."

No biggy, this thread already has more forks() than a Unix daemon.

Your 3rd function is a solenoid actuated spool valve.

Dan