Backhoe bleed down (BX23S)

[ejb11235]

I have a question about backhoe bleed down. The backhoe on my BX23S bleeds down ... if I don't put the pin in, it will be on the ground over night. My understanding is that this is not uncommon, if not actually normal behavior.

I did a test and disconnected all three hydraulic lines, and it still bled down. I haven't run any timing tests so I don't know if disconnecting the lines changes how fast it bleeds down.

EDIT: By "disconnected" I meant disconnected the hydraulic lines that go from the tractor to the backhoe.

It seems to me that the bleed down can either come from internal leakage within the main boom cylinder, or valve leakage. The boom cylinder is extending, so it wouldn't lock out if there was an internal leakage (thanks Dan).

If the boom bleeds down with the hydraulic lines disconnected, is this semi-direct evidence that there's internal cylinder leakage? If not, where else would the displaced fluid from the rod end be going?

Thanks!

 

[Russell King]

Did you put plugs or cap anything on the cylinders?

Describe what you did in more detail please.

 

[ejb11235]

Did you put plugs or cap anything on the cylinders?

Describe what you did in more detail please.

Oh dear I realize I wasn't clear at all. I disconnected the three hydraulic lines that run between the tractor and the backhoe. This wasn't a full-on test, it just prevented any flow outside of the backhoe itself.

Hence my question ... if the fluid can't go back to the tank or reverse through the pump, where else can it go?

 

[lugbolt]

bleed down overnight isn't unusual. The cylinder has a piston inside of it. The piston is not a perfect seal and fluid will leak past the seals even while not using. The amount of leakage is usually minimal-but those cylinders are small and don't have much volume, so a little leakage results in a faster than you'd expect leakdown rate.

Where does the oil go? It's a double-acting cylinder so there are two "chambers" inside of it and the oil in one chamber leaks past the seal into the other.

some folks will open the cylinder and rebuild it but it doesn't always solve the problem; at least not permanently.

Kubota has a spec for leakdown rate, I want to say 2" per hour is considered acceptable but it's been a few years since I've looked and could very well be wrong.

 

[ejb11235]

bleed down overnight isn't unusual. The cylinder has a piston inside of it. The piston is not a perfect seal and fluid will leak past the seals even while not using. The amount of leakage is usually minimal-but those cylinders are small and don't have much volume, so a little leakage results in a faster than you'd expect leakdown rate.

Where does the oil go? It's a double-acting cylinder so there are two "chambers" inside of it and the oil in one chamber leaks past the seal into the other.

some folks will open the cylinder and rebuild it but it doesn't always solve the problem; at least not permanently.

Kubota has a spec for leakdown rate, I want to say 2" per hour is considered acceptable but it's been a few years since I've looked and could very well be wrong.

Thanks lug. I figured it was normal behavior but I thought I'd ask. My phrasing on this question wasn't very good, and made me seem less knowledgeable than I am. Essentially my question was ... "if it's not an internal leak, then where could the fluid be going?" You've confirmed that it most likely is an internal leak and that it's not unusual or even an issue. Really good point about how the low volume makes things go quicker.

 

[Runs With Scissors]

My BH bleeds down overnight as well.

I try to remember to put the "safety latch" on when I leave it, but plenty of times I have forgotten.

I would say that it is "normal".


Edit: One thing that you have to be careful of is where you park it though. One time when the boom leaked down, it was dangerously close to damaging the garage door.

 

[TheOldHokie]

Thanks lug. I figured it was normal behavior but I thought I'd ask. My phrasing on this question wasn't very good, and made me seem less knowledgeable than I am. Essentially my question was ... "if it's not an internal leak, then
Cylinders dont leak internally.
unusual or even an issue. Really good point about how the low volume makes things go quicker.

I am going to flog this dead horse one more time.

1. Leakdown is fundamentally due to spool leakage in the valve. Seals in the çylinder should hold pressure indefinitly. If the seals are leaking internally they are defective.
2. In a double acting single end cylinder pressure can leak both directions but fluid can only leak from rod end to base end (extend). Fluid cannot leak from the base to rod side of the piston (retract).

If you want a reliable and unambiguous test of the piston seals cap/plug the base end port and then apply and hold pressure to the rod end. If the seals are leaking the rod will extend.

Dan

 

[ejb11235]

I am going to flog this dead horse one more time.

1. Leakdown is fundamentally due to spool leakage in the valve. Seals in the çylinder should hold pressure indefinitly. If the seals are leaking internally they are defective.
2. In a double acting single end cylinder pressure can leak both directions but fluid can only leak from rod end to base end (extend). Fluid cannot leak from the base to rod side of the piston (retract).

If you want a reliable and unambiguous test of the piston seals cap/plug the base end port and then apply and hold pressure to the rod end. If the seals are leaking the rod will extend.

Dan

It's about time you showed up. I have been waiting for you.

I have not forgotten our previous discussions on the topic of internal leakage.

I will restate the crux of my original question:

IF there is spool leakage in the valve, and
GIVEN that I had disconnected the hydraulic lines running between the tractor and the backhoe (i.e. pump, tank and power beyond)
WHERE could the fluid leaking in the valve be leaking to?

 

[TheOldHokie]

Leakdown is primarily due to spool leakage in the valve. Seals in the çylinder should hold pressure indefinitly. If the seals are leaking internally they are defective.

In a double acting single end cylinder pressure can leak both directions but fluid can only flow from rod end to base end. It cannot leak from base to rod side of the

If you want a reliable and unambiguous test of the cylinder seals cap the base end port and apply and hold pressure to the rod end. If the seals are leaking the rod will extend.

Dan

It's about time you showed up. I have been waiting for you.

I have not forgotten our previous discussions on the topic of internal leakage.

I will restate the crux of my original question:

IF there is spool leakage in the valve, and
GIVEN that I had disconnected the hydraulic lines running between the tractor and the backhoe (i.e. pump, tank and power beyond)
WHERE could the fluid leaking in the valve be leaking to?

I have no idea but I cant rule internal valve leakage out.

Put a DPOCV on the cylinder circuit and if it continues to leak down the leakage is inside the cylinder. If it stops leaking down its in the valve.

Dan

 

[ejb11235]

I have no idea but I cant rule internal valve leakage out.

Put a DPOCV on the cylinder circuit and if it continues to leak down the leakage is inside the cylinder. If it stops leaking down its in the valve.

Dan

I just came back to edit my last response but you beat me to it.

When the main boom is dropping, the cylinder is extending, so fluid is being displaced from the rod end. So if the valve is leaking then the most obvious explanation is that the displaced rod-end fluid is leaking through the valve to the base-end of the same cylinder. There wouldn't be any lock-out.

Compare this to a drooping FEL ... the loader dropping down would cause the the cylinder(s) to retract, which would cause hydraulic lock-out.

Two questions:
1) is it reasonable to test the valve by connecting the main boom circuit to another valve in the valve block ... like one of the stabilizers? Or would it be better to go a more direct route and disconnect the main boom cylinder and put pressure guages on the ends of the lines? Or do what you suggested with the DPOCV? I'm trying to figure out what's the minimum amount of effort that still provides actionable information.
2) How do I find out what kinds of connections are on the main boom lines where they connect to the cylinder? (I haven't done a web search yet). Is this pretty standard on the BX23S or could it be any number of different types?

Thanks!

 

[TheOldHokie]

I just came back to edit my last response but you beat me to it.

When the main boom is dropping, the cylinder is extending, so fluid is being displaced from the rod end. So if the valve is leaking then the most obvious explanation is that the displaced rod-end fluid is leaking through the valve to the base-end of the same cylinder. There wouldn't be any lock-out.

Compare this to a drooping FEL ... the loader dropping down would cause the the cylinder(s) to retract, which would cause hydraulic lock-out.

Two questions:
1) is it reasonable to test the valve by connecting the main boom circuit to another valve in the valve block ... like one of the stabilizers? Or would it be better to go a more direct route and disconnect the main boom cylinder and put pressure guages on the ends of the lines? Or do what you suggested with the DPOCV? I'm trying to figure out what's the minimum amount of effort that still provides actionable information.
2) How do I find out what kinds of connections are on the main boom lines where they connect to the cylinder? (I haven't done a web search yet). Is this pretty standard on the BX23S or could it be any number of different types?

Thanks!

Raise and lock the boom in tje full up position then discomnect the two hoses on the boom cylinder. Plug/cap both ports on the cylinder and release the lock. If the boom drifts down the cylinder is leaking internally. Thats $2 in diagnostic supplies and a definitive answer in a matter of an hour or two if not less.

Dan

 

[ejb11235]

Raise and lock the boom in tje full up position then discomnect the two hoses on the boom cylinder. Plug/cap both ports on the cylinder and release the lock. If the boom drifts down the cylinder is leaking internally. Thats $2 in diagnostic supplies and a definitive answer in a matter of an hour or two if not less.

Dan

I like it. Thanks!

 

[Henro]

I have a weakness for mental brain twisters at times!

let’s for the sake of argument, assume that the boom cylinder is 100% perfect.

Also assume that the cylinder is extending during the leak down event. (I believe this is correct but I don’t have a BX23S)

The Backhoe has been disconnected from the tractor and the quick disconnects are working perfectly and not leaking.

The boom cylinder gradually extends overtime. There are no leaks apparent and no drips are showing up on the garage floor. The system is perfectly sealed.

But for the boom to drop, fluid must leave the rod end of the cylinder and go somewhere.

Connected between the two ends of the cylinder is the control valve. The two hoses from the boom cylinder are connected to the control valve and nothing else.

The volume of liquid inside each end of the cylinder is different. The rod end has a smaller volume than the base end. So as the rod end extends, if the fluid can find its way back to the base end there’s more than enough room for it

The obvious conclusion is that fluid leaving the rod end finds its way back to the base end of the cylinder, via leakage through the control valve.

That’s where I‘d put my money if I was a betting man. But I learned long time ago not to place bets.

 

[TheOldHokie]

I have a weakness for mental brain twisters at times!

let’s for the sake of argument, assume that the boom cylinder is 100% perfect.

Also assume that the cylinder is extending during the leak down event. (I believe this is correct but I don’t have a BX23S)

The Backhoe has been disconnected from the tractor and the quick disconnects are working perfectly and not leaking.

The boom cylinder gradually extends overtime. There are no leaks apparent and no drips are showing up on the garage floor. The system is perfectly sealed.

But for the boom to drop, fluid must leave the rod end of the cylinder and go somewhere.

Connected between the two ends of the cylinder is the control valve. The two hoses from the boom cylinder are connected to the control valve and nothing else.

The volume of liquid inside each end of the cylinder is different. The rod end has a smaller volume than the base end. So as the rod end extends, if the fluid can find its way back to the base end there’s more than enough room for it

The obvious conclusion is that fluid leaving the rod end finds its way back to the base end of the cylinder, via leakage through the control valve.

That’s where I‘d put my money if I was a betting man. But I learned long time ago not to place bets.

I have a similar weakness but this question is way too ill defined to provoke me.

Dan

 

[ejb11235]

I have a weakness for mental brain twisters at times!

let’s for the sake of argument, assume that the boom cylinder is 100% perfect.

Also assume that the cylinder is extending during the leak down event. (I believe this is correct but I don’t have a BX23S)

The Backhoe has been disconnected from the tractor and the quick disconnects are working perfectly and not leaking.

The boom cylinder gradually extends overtime. There are no leaks apparent and no drips are showing up on the garage floor. The system is perfectly sealed.

But for the boom to drop, fluid must leave the rod end of the cylinder and go somewhere.

Connected between the two ends of the cylinder is the control valve. The two hoses from the boom cylinder are connected to the control valve and nothing else.

The volume of liquid inside each end of the cylinder is different. The rod end has a smaller volume than the base end. So as the rod end extends, if the fluid can find its way back to the base end there’s more than enough room for it

The obvious conclusion is that fluid leaving the rod end finds its way back to the base end of the cylinder, via leakage through the control valve.

That’s where I‘d put my money if I was a betting man. But I learned long time ago not to place bets.

Yes, on the BX23S, the cylinder extends to make the boom go down. So yes, this is how it would work if the valve is leaking. If the cylinder is leaking then the fluid just goes past the seal in the cylinder and directly into the base end.

 

[ejb11235]

I have a similar weakness but this question is way too ill defined to proke me.

Dan

LOL, the question so far has been purely hypothetical.

This would be the point in the process where actual evidence needs to be obtained. That may not happen for quite a while due to other distractions.

Having said that, my next step would be to figure out what caps and plugs I need to get.

Thanks!

 

[lugbolt]

I have a weakness for mental brain twisters at times!

let’s for the sake of argument, assume that the boom cylinder is 100% perfect.

Also assume that the cylinder is extending during the leak down event. (I believe this is correct but I don’t have a BX23S)

The Backhoe has been disconnected from the tractor and the quick disconnects are working perfectly and not leaking.

The boom cylinder gradually extends overtime. There are no leaks apparent and no drips are showing up on the garage floor. The system is perfectly sealed.

But for the boom to drop, fluid must leave the rod end of the cylinder and go somewhere.

according to some of my customers, that fluid must teleport to an unknown dimension or something

The obvious conclusion is that fluid leaving the rod end finds its way back to the base end of the cylinder, via leakage through the control valve.

That’s where I‘d put my money if I was a betting man. But I learned long time ago not to place bets.

that's where I was going, regardless of how technical it is. 99% of the leakdowns of loaders and backhoes are cylinder related and not so much valve related in my experience. The few that had leaking valves (on most of the tractors anyway), also leaked externally since the spool bores were just plum wore out.

 

[TheOldHokie]

according to some of my customers, that fluid must teleport to an unknown dimension or something



that's where I was going, regardless of how technical it is. 99% of the leakdowns of loaders and backhoes are cylinder related and not so much valve related in my experience. The few that had leaking valves (on most of the tractors anyway), also leaked externally since the spool bores were just plum wore out.

Nonsense.

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.

A fresh cylinder on the other hand will hold for weeks going on months. Thats why hydraulic top links are routinely sold with DPOCV lock valves which prevent reverse flow through the control valve. Valve manufacturers also make valves with optional DPOCV locks on the valve itself.

Dan

 

[PoTreeBoy]

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.

 

[TheOldHokie]

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.

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