BH77 boom cylinder droops

[TheOldHokie]

Maybe I should start a new thread, but I have the drooping problem as well and the previous information is pertinent to my question. I have the BH70 backhoe, the parts diagram shows the relief valves like the BH77, but with slightly different part numbers, I see no relief valves like that on mine. Maybe there was a change and the parts list is not up to date. I would think that there must be pressure relief, so does anyone know if relief valves are now embedded inside the valve block?

I believe those are port reliefs which are typically screw in cartridges. Not enough room to put them in the body.

Dan

 

[lynnmor]

I believe those are port reliefs which are typically screw in cartridges. Not enough room to put them in the body.

Dan

Therein lies the problem, they don't exist.
Here is the parts break-down, the reliefs are 140 & 150:

 

[TheOldHokie]

Therein lies the problem, they don't exist.
Here is the parts break-down, the reliefs are 140 & 150:

View attachment 75766

Yes I looked before I posted. There is no port relief on the boom cylinder. It appears your problem is something else.

Dan

 

[ruger1980]

The parts diagram is showing port reliefs for the swing, boom and dipper spools.

 

[ruger1980]

Maybe I should start a new thread, but I have the drooping problem as well and the previous information is pertinent to my question. I have the BH70 backhoe, the parts diagram shows the relief valves like the BH77, but with slightly different part numbers, I see no relief valves like that on mine. Maybe there was a change and the parts list is not up to date. I would think that there must be pressure relief, so does anyone know if relief valves are now embedded inside the valve block?

You say "drooping down" Do you mean the boom is drifting down and if so does this happen while operating or while suspended in the air. Also what is the rate of drift?

 

[lynnmor]

The parts diagram is showing port reliefs for the swing, boom and dipper spools.

Yep, but my valve assembly appears different and there are no relief valves shooting out of it anywhere. Here is the name tag:

 

[lynnmor]

You say "drooping down" Do you mean the boom is drifting down and if so does this happen while operating or while suspended in the air. Also what is the rate of drift?

This is a new tractor and the cylinder has been rebuilt which reduced the drift greatly. The drift happens whether running or not. The current drift is roughly 2" per hour with the engine off in very cold conditions. My main concern is that the drift will increase considerably when warm weather and long operating times return. I would like to get this thing working better now so that it won't be tied up all summer, unlike last summer. I tried disconnecting the lines from the tractor to eliminate oil from being transferred back to the tank or elsewhere, but nothing changed. My current thinking is that the valve body it faulty or the cylinder is sucking air around the shaft. For a cylinder to move it needs to have a fluid (air or oil) going in or out of it.

 

[Henro]

This is a new tractor and the cylinder has been rebuilt which reduced the drift greatly. The drift happens whether running or not. The current drift is roughly 2" per hour with the engine off in very cold conditions. My main concern is that the drift will increase considerably when warm weather and long operating times return. I would like to get this thing working better now so that it won't be tied up all summer, unlike last summer. I tried disconnecting the lines from the tractor to eliminate oil from being transferred back to the tank or elsewhere, but nothing changed. My current thinking is that the valve body it faulty or the cylinder is sucking air around the shaft. For a cylinder to move it needs to have a fluid (air or oil) going in or out of it.

I do not see a problem myself. That drift down is 1/2 inch in 15 minutes. How is this an issue when operating the backhoe?

My backhoe has a boom lock, so when not using it I can flip the lock in place in about 5 seconds, and not worry about it. Mine has certainly always leaked down. Never bothered to measure the rate because it never was an issue when using the backhoe.

How is this 2" per hour leak down causing you problems?

edit: Being one that overthinks things occasionally, I understand your concern regarding the possibility of things leaking down faster when hot.

But even if leak down doubled when hot, would 4" per hour be an issue? That is still only 1" per 15 minutes. When using my backhoe the boom rarely stays still for 15 seconds...And I usually set the bucket on the ground when getting off to do something.

 

[TheOldHokie]

Yep, but my valve assembly appears different and there are no relief valves shooting out of it anywhere. Here is the name tag:

View attachment 75801

This is a new tractor and the cylinder has been rebuilt which reduced the drift greatly. The drift happens whether running or not. The current drift is roughly 2" per hour with the engine off in very cold conditions. My main concern is that the drift will increase considerably when warm weather and long operating times return. I would like to get this thing working better now so that it won't be tied up all summer, unlike last summer. I tried disconnecting the lines from the tractor to eliminate oil from being transferred back to the tank or elsewhere, but nothing changed. My current thinking is that the valve body it faulty or the cylinder is sucking air around the shaft. For a cylinder to move it needs to have a fluid (air or oil) going in or out of it.

If a single rod DA cylinder is fully filled with oil some volume of that oil has to exit the cylinder in order for the rod to retract. Potential points of leakage are control valve spool, port reliefs, rod seals. Spool leakage is virtually guaranteed. A typical rate would be 5-15 cc/second. You have 2" per hour drift. Do a little arithmetic using thosecnumbers and see how it compares.

Dan

 

[lynnmor]

As I said " My main concern is that the drift will increase considerably when warm weather and long operating times return. "

Last summer on the first use, the bucket was on the ground after driving less than 200 yards. They rebuilt the cylinder but I am not comfortable that it is fixed and the warranty clock is always ticking. Again, for a cylinder to move, air or oil needs to enter or leave it, I am trying to find the source of that. The dealer will be here in a week to fix the faulty routing of the steel lines that happened when they rebuilt the cylinder, if I can come up with the source of the drooping maybe it can be addressed at that time. And yes, it is possible it is sucking air at the fittings they need to remove, but I have seen only a trace of oil there.

I need to pin the boom up so that may not be as convenient as your system.

 

[Henro]

Spool leakage is virtually guaranteed. A typical rate would be 5-15 cc/second. You have 2" per hour drift. Do a little arithmetic using thosecnumbers and see how it compares.

Dan

Dan, I have to ask because it just seems like 5-15 cc/second leakage would be extremely high. That would equate to 300 CC to nearly a liter per minute...

If it were 5-15 cc/min I would not be asking...my guess is that is a typo?

Like you said, if there is no leak from hoses/connections, where else could the fluid be going except somehow through the control valve and back to the tank. Still...2" per hour is a non issue for me.

 

[TheOldHokie]

Dan, I have to ask because it just seems like 5-15 cc/second leakage would be extremely high. That would equate to 300 CC to nearly a liter per minute...

If it were 5-15 cc/min I would not be asking...my guess is that is a typo?

Like you said, if there is no leak from hoses/connections, where else could the fluid be going except somehow through the control valve and back to the tank. Still...2" per hour is a non issue for me.

My bad and good eyes - that should be per minute.

Dan

 

[lynnmor]

I tried disconnecting from the tractor, as stated in a previous post, so nothing is going to the tank and nothing changed. The boom cylinder lengthens to cause a droop, and it only needs to move a small amount to get a few inches at the bucket so that is part of the problem. Since fluid, air or water, needs to be added to the cylinder, I am going to do a test with the bucket pushing on the ground and see if the shaft seal expels any oil, maybe it sucks air in the opposite direction. I do understand that some movement can be expected over time, I'm only trying to understand a system that shows relief valves on the parts list and there are none. When this thing reaches an unacceptable rate of droop, like it did last summer, I want to be prepared to act.

 

[Henro]

I tried disconnecting from the tractor, as stated in a previous post, so nothing is going to the tank and nothing changed. The boom cylinder lengthens to cause a droop, and it only needs to move a small amount to get a few inches at the bucket so that is part of the problem. Since fluid, air or water, needs to be added to the cylinder, I am going to do a test with the bucket pushing on the ground and see if the shaft seal expels any oil, maybe it sucks air in the opposite direction. I do understand that some movement can be expected over time, I'm only trying to understand a system that shows relief valves on the parts list and there are none. When this thing reaches an unacceptable rate of droop, like it did last summer, I want to be prepared to act.

Interesting. When the cylinder extends, less volume is displaced in the rod side of the cylinder than is vacated by the piston end of the cylinder. So how can the volumes be maintained? With the hydraulics disconnected from the tractor?

So maybe either a partial vacuum is being created on the piston end of the cylinder, or there is a leak in a fitting where air is coming into the system.

Just speculation. Let those with better knowledge and experience chime in.

 

[TheOldHokie]

Interesting. When the cylinder extends, less volume is displaced in the rod side of the cylinder than is vacated by the piston end of the cylinder. So how can the volumes be maintained? With the hydraulics disconnected from the tractor?

So maybe either a partial vacuum is being created on the piston end of the cylinder, or there is a leak in a fitting where air is coming into the system.

Just speculation. Let those with better knowledge and experience chime in.

If the piston seal is leaking a load on the rod will pull a vacuum on the base end.

Dan

 

[lynnmor]

If the piston seal is leaking a load on the rod will pull a vacuum on the base end.

Dan

I believe that great minds are thinking alike. I hope to do the bucket pushing on ground test tomorrow, if I see oil the seal might be the culprit. It ain't a perfect test because a seal can be fine under pressure but leak under a vacuum.

Thanks Henro and Hokie, your input is appreciated.

 

[lugbolt]

I forget what the acceptable drift rate was, but I think you're within spec. It has a mechanical boom lock for this very reason.

U might check dealer and ask them what the acceptable rate of drop is. I want to say 3" per hour measured at the cylinder but may be wrong.

 

[kennyroy]

The boom cylinder is drooping on my BH77 which is on a 2008 L3400 HST with 600 hours. There is no fluid leaking anywhere. I put a blue Viagra pill in the hydraulic reserve, but it still droops overnight. Haha... anyways, when digging and the tractor is warmed up it suddenly won't lift the arm and bucket up. I have to wait a couple of seconds and then pull back on both levers to get it up. The dipper and bucket cylinders appear to work fine. When parked the boom droops unless the safety latch is set.
I Took the rig to the Kubota dealer and they recommend replacing the Control Value and Pressure Check Value for $2360!? What the...$$! They're charging me $400 just for doing diagnostics on the boom cylinder line to determine that the pressure was indeed fluctuating. I'm bringing the rig home and plan to take the control value and pressure relief value apart, clean it, reassemble and hope that in the process I find a bad o-ring or some obvious reason for the leakage.
Anyone have advice about this drooping issue beyond buying the backhoe flowers and dinner or has anyone done a control value rebuild? I've seen the job referred to in threads but no details.

Pressure relief valve!

 

[whitetiger]

Pressure relief valve!

The post you replied to is almost 14 months old, and 9 out of ten times it is a circuit relief valve.