Backhoe / Hydraulics question

Jay4200 · May 30, 2006

Questions regarding my backhoe and the health of it's hydraulic system. Woods BH9000 using tractor's hydraulics, BTW.

Power -- Out of the three main degrees of digging freedom, power from strong to weak goes: bucket curl, boom lift, dipper.

Dipper joint hold-off strength -- the dipper joint can move in response to bucket curl torque (if it is extended). For example, if I hook the bucket around a rock with the arm mostly extended, then curl the bucket to move the rock toward me (pressing against the dirt behind the rock), the dipper joint may straighten out slightly. I can imagine that the torque imposed on the dipper joint by the bucket curl pressure could exceed the blow-off pressure (I know my elbow is pretty weak at full extension), so it seems like this could easily be normal, but I figured I'd ask.

My boom leaks down such that about 1" of shaft is exposed overnight. Does this sound OK? Bucket curl doesn't appear to leak down at all. Haven't done a dipper leak-down test yet.

Thanks - Jay

Jay4200 · May 30, 2006

Questions regarding my backhoe and the health of it's hydraulic system. Woods BH9000 using tractor's hydraulics, BTW.

Power -- Out of the three main degrees of digging freedom, power from strong to weak goes: bucket curl, boom lift, dipper.

Dipper joint hold-off strength -- the dipper joint can move in response to bucket curl torque (if it is extended). For example, if I hook the bucket around a rock with the arm mostly extended, then curl the bucket to move the rock toward me (pressing against the dirt behind the rock), the dipper joint may straighten out slightly. I can imagine that the torque imposed on the dipper joint by the bucket curl pressure could exceed the blow-off pressure (I know my elbow is pretty weak at full extension), so it seems like this could easily be normal, but I figured I'd ask.

My boom leaks down such that about 1" of shaft is exposed overnight. Does this sound OK? Bucket curl doesn't appear to leak down at all. Haven't done a dipper leak-down test yet.

Thanks - Jay

Jay4200 · May 30, 2006

In case I'm not clear - does all of the above sound normal? Does anything sound excessive and/or indicative of blow-by?

thanks - Jay

Jay4200 · May 30, 2006

In case I'm not clear - does all of the above sound normal? Does anything sound excessive and/or indicative of blow-by?

thanks - Jay

JerryG · May 30, 2006

My boom leaks down such that about 1" of shaft is exposed overnight. Does this sound OK? Bucket curl doesn't appear to leak down at all. Haven't done a dipper leak-down test yet. 
Very few compact loaders or backhoes don't leak down. The rate that you stated is very good for leak down. The best thing to do is either put the transport pin in or let it down to the ground when it isn't in use to relieve the pressure on the valves and cylinder packing.

JerryG · May 30, 2006

My boom leaks down such that about 1" of shaft is exposed overnight. Does this sound OK? Bucket curl doesn't appear to leak down at all. Haven't done a dipper leak-down test yet. 
Very few compact loaders or backhoes don't leak down. The rate that you stated is very good for leak down. The best thing to do is either put the transport pin in or let it down to the ground when it isn't in use to relieve the pressure on the valves and cylinder packing.

dfkrug · May 31, 2006

( Dipper joint hold-off strength -- the dipper joint can move in response to bucket curl torque (if it is extended). For example, if I hook the bucket around a rock with the arm mostly extended, then curl the bucket to move the rock toward me (pressing against the dirt behind the rock), the dipper joint may straighten out slightly. I can imagine that the torque imposed on the dipper joint by the bucket curl pressure could exceed the blow-off pressure (I know my elbow is pretty weak at full extension), so it seems like this could easily be normal, but I figured I'd ask.
)

How much is "slightly"? If your dipper stick moves at all
with its valve closed, then it is due to air in the cylinder or
a leaking internal cyl seal, or a leaky valve itself. If you
have only a 1" leakdown overnight under pressure, then I
would lean toward air in the cylinder. Of course, loose
pins could give you a lot of wiggle room, too.

dfkrug · May 31, 2006

( Dipper joint hold-off strength -- the dipper joint can move in response to bucket curl torque (if it is extended). For example, if I hook the bucket around a rock with the arm mostly extended, then curl the bucket to move the rock toward me (pressing against the dirt behind the rock), the dipper joint may straighten out slightly. I can imagine that the torque imposed on the dipper joint by the bucket curl pressure could exceed the blow-off pressure (I know my elbow is pretty weak at full extension), so it seems like this could easily be normal, but I figured I'd ask.
)

How much is "slightly"? If your dipper stick moves at all
with its valve closed, then it is due to air in the cylinder or
a leaking internal cyl seal, or a leaky valve itself. If you
have only a 1" leakdown overnight under pressure, then I
would lean toward air in the cylinder. Of course, loose
pins could give you a lot of wiggle room, too.

john_bud · May 31, 2006

It sounds all normal to me. The strength is all about the leverage from the hydraulics and the physical set up. The curl is typically physically the most advantageous. Movement speed is related to cylinder size and pump volume/rpm.

How old is your hoe? Operating hours? If it is new, you may have air. Air can be purged by extending the cylinder all the way and hold the control to force it against the stop for a count of 5, then all the way back and against the stop for a count of 5. Do that 3-5 times in a row for each cylinder. Check the fluid level in the res before and after, with the loader and hoe in the exact same position. If there was air, it should be lower. If there was a lot of air, it may even look foamy for a short while. Mine did when I put a rebuilt cylinder in.

The overnight sag sounds normal.

jb

john_bud · May 31, 2006

It sounds all normal to me. The strength is all about the leverage from the hydraulics and the physical set up. The curl is typically physically the most advantageous. Movement speed is related to cylinder size and pump volume/rpm.

How old is your hoe? Operating hours? If it is new, you may have air. Air can be purged by extending the cylinder all the way and hold the control to force it against the stop for a count of 5, then all the way back and against the stop for a count of 5. Do that 3-5 times in a row for each cylinder. Check the fluid level in the res before and after, with the loader and hoe in the exact same position. If there was air, it should be lower. If there was a lot of air, it may even look foamy for a short while. Mine did when I put a rebuilt cylinder in.

The overnight sag sounds normal.

jb