Nah - QWERTY is the way to goI'd install a QRSTUV to control drift on Sundays and Wednesdays.
Right. I was just clarifying that there's a reason they aren't more common. Didn't think about the reliefs.To be clear I was not suggesting a DPOCV for actual use on a backhoe. In addition to the jerky operation it would prevent operation of the port reliefs (which are another potential leakdown point).
Dan
I should have done both in the original post. I am getting carelessRight. I was just clarifying that there's a reason they aren't more common. Didn't think about the reliefs.
BINGO!My 2¢.
1¢ You wouldn't like operating the boom with DPOCV's installed, they tend to jerk when releasing the check.
2¢ You really should develop the habit of 'inerting' your rig when shutting down. After you stop the engine, whether storage pins are in place or not, move all control handles to let all attachments down and release the hydraulic pressure. A person or dog or ? could inadvertently hit a handle and cause an accident.
OK, I'm learning but PerPlexed (try it) about WhatIsA "DPOCV " ...To be clear I was not suggesting a DPOCV for actual use on a backhoe. In addition to the jerky operation it would prevent operation of the port reliefs (which are another potential leakdown point).
Dan
In simple terms its a pair of check valves that are installed on a double acting cylinder. There is one check for each port on the cylinder and the checks act as positive shutoffs that prevent reverse flow from the cylinder. The effect is to eliminate cylinder drift caused by internal leakage in the control valve.OK, I'm learning but PerPlexed (try it) about WhatIsA "DPOCV " ...
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A Double Pilot Operated Check Valve (DPOCV) is a specialized type of non-return valve used in hydraulic systems to control fluid flow and maintain load stability. It allows fluid to flow freely in one direction and prevents flow in the opposite direction unless actuated by pilot pressure. This valve is equipped with two pilot lines, enabling control in both directions of a hydraulic circuit. Each pilot line is connected to a seat; when pressure is applied, it opens the corresponding seat, allowing reverse flow.
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There used to be a booklet at IBM that explained the Acronyms. About 60 pages....
I do install the storage pins when I park the tractor overnight and lower the FEL and set the parking brake.My 2¢.
1¢ You wouldn't like operating the boom with DPOCV's installed, they tend to jerk when releasing the check.
2¢ You really should develop the habit of 'inerting' your rig when shutting down. After you stop the engine, whether storage pins are in place or not, move all control handles to let all attachments down and release the hydraulic pressure. A person or dog or ? could inadvertently hit a handle and cause an accident.
Dan -- this is really helpful ... I actually didn't know that spool valves always leak. That explains a lot.Every spool valve made leaks straight from the factory. Its the inescapable nature of the spool valve design - they are not positive shutoff devices. Valve manufacturers document spool leakage rates in their catalogs. For a 10 GPM valve a typical value would be somrthing around 3-10 cc per minute. On a 2" cylinder that equates to 1 inch drift in 5-20 minutes. i am sure thats how Kubota gets their specifications for allowable drift.
The spools in a directional control valve do not have any sort of elastomeric seals on the spools. Instead they rely on a very close sliding fit in the body of the valve for the "seal". Since there has to be some radial clearance to allow the spool to move that is not a positive shutoff mechanism and there is always a path for high pressure oil to seep around the spool.Dan -- this is really helpful ... I actually didn't know that spool valves always leak. That explains a lot.
Good to know ... I'll update my mental image of what the inside of the spool valve looks like!The spools in a directional control valve do not have any sort of elastomeric seals on the spools. Instead they rely on a very close sliding fit in the body of the valve for the "seal". Since there has to be some radial clearance to allow the spool to move that is not a positive shutoff mechanism and there is always a path for high pressure oil to seep around the spool.
Dan
Then why when we completely isolate the cylinder, does it still leak down at the same rate?Nonsense.
Every spool valve made leaks straight from the factory. Its the inescapable nature of the spool valve design
Are you completely isolating the cylinder, or just detaching the whole backhoe assembly from the tractor? Leaving the spool valve attached.Then why when we completely isolate the cylinder, does it still leak down at the same rate?
I don't know what your question is.Then why when we completely isolate the cylinder, does it still leak down at the same rate?
OK. I read your posts as on-the-tractor.I do install the storage pins when I park the tractor overnight and lower the FEL and set the parking brake.
I'm still figuring out how to position the boom and dipper when the backhoe is off the tractor.
Cylinders can be rebuilt. Seals are elastomeric- typically orings with backup washers and wipers. Barrels get worn and scored but can be honed. At some point its cheaper to replace them.Dan said:
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A DA cylinder can leak internally but a new one should not and should hold rated pressure for days on end. Internal piston seals wear with age and develop leakage, That leakage can cause cylinder drift in the extend direction but never retract.
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Dan, the cylinders on my D7100 have a flat (for a wrench??) on one end. Can this type of cylinder be rebuilt / have piston seals replaced? Are these the type of seals that expand under pressure and can handle some wear?
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All directional control spool valves leak internally right out of the box and will allow a cylinder to drift in both directions. Leakage rates out of the box are around 5 cc/min for the types of valves we are discussing. They get worse as they are used and the spools/housings develop wear.
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Dan, can spool valves be "rebuilt" by electroplating them to a slightly larger diameter? Some engine cylinders have been resized this way..
AND:?
Do DA cylinders leak down more in one direction than the other?
IS this why a FEL bucket cylinder leaks down more than the lift cylinders? If so, can the bucket cylinders be installed the "Other Side Up"
Many of us seem to be working to keep Dan busy! Thanks Dan!