Backhoe bleed down (BX23S)

[hagrid]

I'd install a QRSTUV to control drift on Sundays and Wednesdays.

 

[TheOldHokie]

I'd install a QRSTUV to control drift on Sundays and Wednesdays.

Nah - QWERTY is the way to go

 

[PoTreeBoy]

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

Right. I was just clarifying that there's a reason they aren't more common. Didn't think about the reliefs.

 

[TheOldHokie]

Right. I was just clarifying that there's a reason they aren't more common. Didn't think about the reliefs.

I should have done both in the original post. I am getting careless

Dan

 

[fried1765]

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.

BINGO!

 

[TerryKing]

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

OK, I'm learning but PerPlexed (try it) about WhatIsA "DPOCV " ...
-------
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.
-------
There used to be a booklet at IBM that explained the Acronyms. About 60 pages....

 

[TheOldHokie]

OK, I'm learning but PerPlexed (try it) about WhatIsA "DPOCV " ...
-------
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.
-------
There used to be a booklet at IBM that explained the Acronyms. About 60 pages....

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.

Actuating pressure applied to to one of the cylinder ports acts as a pilot pressure that automagically unlocks the opposing check allowing normal cylinder operation. When the control valve is returned to neutral the loss of pilot pressure automagically restores the checks.

Dan

 

[ejb11235]

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.

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.

 

[ejb11235]

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.

Dan -- this is really helpful ... I actually didn't know that spool valves always leak. That explains a lot.

 

[TheOldHokie]

Dan -- this is really helpful ... I actually didn't know that spool valves always leak. That explains a lot.

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

 

[ejb11235]

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

Good to know ... I'll update my mental image of what the inside of the spool valve looks like!

beginning mental image update procedure ....
deleting o-ring ... deletion sequence completed ....
saving mental image ...
mental image update complete

 

[John T]

sorry if this has been said already.... kinda glanced through the replies...

yes it will bleed down if not supported....
(when off the tractor)

If I take it off for more than a day, I will make sure the pin is in ... and also block it

Otherwise... If it bleeds down too much/ or puts too much pressure in the lines.... You won't be able to connect the flat faced couplers....

fix for that is 2 metric adjustable wrenches.... unscrew the coupler/ release pressure.... tighten back up..

pain in the arse...

always happens when you are in a hurry to do sumpthin....

 

[lugbolt]

Nonsense.

Every spool valve made leaks straight from the factory. Its the inescapable nature of the spool valve design

Then why when we completely isolate the cylinder, does it still leak down at the same rate?

 

[PaulL]

Then why when we completely isolate the cylinder, does it still leak down at the same rate?

Are you completely isolating the cylinder, or just detaching the whole backhoe assembly from the tractor? Leaving the spool valve attached.

 

[TheOldHokie]

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.

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.

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.

So with that in mind can you rephrase your question?

Dan

 

[PoTreeBoy]

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.

OK. I read your posts as on-the-tractor.

 

[TerryKing]

Dan said:
---
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.
---

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?

---
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.
---
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!

 

[TheOldHokie]

Dan said:
---
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.
---

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?

---
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.
---
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!

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.

Small spool valves are not normally repairable. A replacement worksection for a small sectional might cost as little as $150. Big expensive valves can be repaired with honing, and fitment of oversize spools. We are talking .001 or less in many cases.

Rod end has a smaller volume and the cylinder will drift faster on extend than retract

Dan

 

[ejb11235]

OK. I read your posts as on-the-tractor.

Yes, up until now I was talking about on-the-tractor. I install the safety pins when the back hoe is on the tractor. But when I take the backhoe off...I'm still figuring out how to store it...oh face palm...if I put the safety pins in then the boom drift won't happen...I'll have to see if I can get it stable with the boom locked in position.