Boom on Woods BH9000 backhoe leaksdown?

[unioncreek]

I have a Woods BH9000 backhoe on my L3710. The dipper leaks down pretty quick when I move the tractor. What’s the best way to tell if the valve or the cylinder itself is the cause?

Bob

 

[TheOldHokie]

I have a Woods BH9000 backhoe on my L3710. The dipper leaks down pretty quick when I move the tractor. What’s the best way to tell if the valve or the cylinder itself is the cause?

Bob

If the cylinder is retracting it can only be the valve.

If its extending you can.test the cylinder by disconnecting the base end hose and plugging the port on the cylinder. Operate valve to retract cylinder and if there os an internal leak it will extend instead.

Dan

 

[unioncreek]

Dan,
Thanks for the info. Yes the cylinder is retracting. I’m not that knowledgeable about hydraulic and figured i had better ask.
Bob

 

[ejb11235]

If the cylinder is retracting it can only be the valve.

This is something I've wondered about ... is it possible for a the piston seal to be leaking enough to allow (in this case) the dipper stick to sag, but not leaking so much that the pump can overcome the leakage to pressurize and retract the cylinder? Or is it pretty much an all-or-nothing deal?

 

[ejb11235]

If its extending you can.test the cylinder by disconnecting the base end hose and plugging the port on the cylinder. Operate valve to retract cylinder and if there is an internal leak it will extend instead.

Why do you say "if it's extending"? Wouldn't the test still work? Or is the point that if it's leaking down in extension, but also not extending under pressure, then it's clearly an internal leak and not the valve so there's no point in testing?

 

[TheOldHokie]

Why do you say "if it's extending"? Wouldn't the test still work? Or is the point that if it's leaking down in extension, but also not extending under pressure, then it's clearly an internal leak and not the valve so there's no point in testing?

I was simply differentiating cases.

If its collapsing under load it has to be from an external leak not internal piston seals. You know that without any additional testing.

There could still be an internal leak causing other problems like loss of extension force or drift in the extend direction. In that case you need to test the cylinder to differentiate internal versus external.

And of course it could be both internal and external.

Dan

 

[TheOldHokie]

This is something I've wondered about ... is it possible for a the piston seal to be leaking enough to allow (in this case) the dipper stick to sag, but not leaking so much that the pump can overcome the leakage to pressurize and retract the cylinder? Or is it pretty much an all-or-nothing deal?

If there is sufficient flow and the leak is relatively small the pump can overwhelm the leak but the cylinder wont hold under static load.

Dan

 

[TheOldHokie]

Dan,
Thanks for the info. Yes the cylinder is retracting. I’m not that knowledgeable about hydraulic and figured i had better ask.
Bob

I.think you misunderstood what was asking. See my responses to ejb11235.

Dan

 

[ejb11235]

Thanks Dan for both of your responses. My BX23S backhoe exhibits leak-downs and one other characteristic I find mildly irritating. The backhoe works fine and I'm not even sure any of the behaviors are out-of-spec, but I find myself curious about the causes and how to determine whether the cause is valves or cylinders. There's a particular behavior that I posted on about a year ago but wasn't able to clearly articulate what was going on, so I deleted the post. I'm using my backhoe a bunch right now so maybe I'll see if I can take a video.

 

[TheOldHokie]

Thanks Dan for both of your responses. My BX23S backhoe exhibits leak-downs and one other characteristic I find mildly irritating. The backhoe works fine and I'm not even sure any of the behaviors are out-of-spec, but I find myself curious about the causes and how to determine whether the cause is valves or cylinders. There's a particular behavior that I posted on about a year ago but wasn't able to clearly articulate what was going on, so I deleted the post. I'm using my backhoe a bunch right now so maybe I'll see if I can take a video.

The central point I am trying to make is when a cylinder drifts in the retract direction it can only be a leak in the valve controlling the cylinder or an exyernal leak in the cylinder or plumbing. It cannot be caused by internal leakage past piston seals.

Drift in the other direction (extend) is the same except that in this direction leaking piston seals can also be a cause.

Dan

 

[ejb11235]

The central point I am trying to make is when a cylinder drifts in the retract direction it can only be a leak in the valve controlling the cylinder or an exyernal leak in the cylinder or plumbing. It cannot be caused by internal leakage past piston seals.

Drift in the other direction (extend) is the same except that in this direction leaking piston seals can also be a cause.

Dan

Damnit I keep forgetting things you've already taught me. Internal leakage cannot explain leak-down in the retract direction because the amount of fluid displaced on the base end of the cylinder is greater than the volume that can be accepted on the rod side. Arg! You explained this to me a couple of years ago on a discussion about float and I asked why you can't simply connect the extend and retract ports.