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