Need Some Hydraulic Troubleshooting Help

[redgoldwing]

Hi! I've got a Kubota L3750 tractor with a Westendorf TA25 Front End Loader. My problem is that the loader bucket slowly sinks from the raised position to the ground (the curl of the bucket maintains whatever angle it was left at).

I'm new to using farm equipment so I need some real basic help on troubleshooting this problem.

Thanks,
Bill Campbell
Pink Ribbon Farm
Oxford, PA

 

[J_J]

Check the valve lever centering springs.

Cyl seals might be worn out.

Valve spool might be leaking.

 

[redgoldwing]

J. J. Thanks. You've told me what to check but, as I said, I need basic help. How do I check these items?

Thanks,
Bill Campbell
Pink Ribbon Farm
Oxford, PA

 

[allenr]

Common to every loader I've had experience with.

I wouldn't worry too much about it.

 

[oldnslo]

Hi! I've got a Kubota L3750 tractor with a Westendorf TA25 Front End Loader. My problem is that the loader bucket slowly sinks from the raised position to the ground (the curl of the bucket maintains whatever angle it was left at).

I'm new to using farm equipment so I need some real basic help on troubleshooting this problem.

Thanks,
Bill Campbell
Pink Ribbon Farm
Oxford, PA

Bill,
how fast does it drop? several inches per second or inch a minute, inch per hour, etc..

Slow leak down or inch per hour is not unusual depending age and condition of equipment.

Faster leak down a simple test with the engine off. VERY Slowly move the lever a small amount like you are trying to raise the FEL. IF you can actually see the directional valve watch the spool move. Move it 1/32 of an inch and hold it there. Did the speed of the loader change? Move it the opposite direction like you are lowering the FEL a 1/32 of an inch. Does the speed change? If it gets slower when moving it one direction or the other this is an idication that your spool may not be returning to center.

BEFORE doing any of the following fully lower the FEL.

First I would check all the linkage from the control lever to the valve to make sure nothing is binding.

Can you post some pictures of the directional valve.

Most valves have the centering springs on the oposite end from the control lever. These are usually accessed by removing a cover. These covers usually are held on with 2 or more screws. If you are comfortable doing this start removing the screws. Does it feel like there is spring tension pushing the cover off? If yes be ready to catch parts as you finish removing the screws. No parts should fly out but..... **it happens. Look for twigs, pebbles, soy beans,(mice) etc in this housing. Clean it up and reinstall the cover.

On every FEL I have seen the cylinders extend to lift and retract to lower so the cylinder seals are not an issue. Cylinder can't retract unless there is an external leak.

Roy

 

[J_J]

If you were to lift the bucket in the air, and shut off the engine, how fast will the bucket drop?
Will it drop to the ground in 24 hrs?

With the engine running, and bucket about midway, does the lift arms descend on their own?

One postive check to eliminate the valve is to add a needle valve in the A work port. This should be the hose feeding the cyl base end port. So raise the lift arms in the air and close off the needle valve, If the cyl are good, this should lock the cyl in place. If the arms drift down, that means that the cyl piston seals are leaking. Just one of the seals can leak and the cyl will not hold. You can determine which cyl is leaking, by using the same needle valve on just one cyl.

For a valve to be considered bad as far as holding the pressure, there is a fluid drops per minute rating . Each manufacturer has there own limits, but it is what you think is not acceptable, that is important.

Roy,

I don't understand your last paragraph. If your seals are leaking, and you have a force pushing or pulling, the fluid will transfer to the other side of the piston to a certain point. The base side of the piston has more fluid than the rod side.

 

[oldnslo]

Roy,

I don't understand your last paragraph. If your seals are leaking, and you have a force pushing or pulling, the fluid will transfer to the other side of the piston to a certain point. The base side of the piston has more fluid than the rod side.

JJ,
Based on the following assumptions the cylinder will move very little or not at all with bad seals.

1) Cylinder is double acting and full of oil.
2) Load is in the direction of forcing the cylinders to retract.
3) No external leakage path from either cylinder port.

Reason being that under these conditions there is more volume in cap end than there is in the rod end. Oil does not compress so there is no room for the oil to transfer from the cap end to the rod end. Cylinder will move until the pressure is equal at both ports and then stop.

Does this make sense?

Roy

 

[redgoldwing]

Sorry for not replying sooner, I've been out of town. The bucket lowers several inches an hour. If I leave the bucket up at about 5' off the ground overnight, in the morning it's on the ground. I'll work on getting a picture to post of the control valve.

Thanks,
Bill Campbell
Pink Ribbon Farm
Oxford, PA

 

[redgoldwing]

Sorry for not replying sooner, I've been out of town. The bucket lowers several inches an hour. If I leave the bucket up at about 5' off the ground overnight, in the morning it's on the ground. I'll have to pick up a needle valve to perform the test you recommend.

Thanks,
Bill Campbell
Pink Ribbon Farm
Oxford, PA

 

[J_J]

After you have installed the needle valves, raise the lift arms about 5 ft, and close off the valve, The only way the cyl can descend is if the seals are leaking, and with the fluid closed off to the cyl, the cyl will try and equalize the pressure internally. If there is a load, it should fall faster.

You can do this with yur tilt cyl also.

 

[redgoldwing]

Thanks JJ.

Bill Campbell
Pink Ribbon Farm
Oxford, PA

 

[jinman]

Redgoldwing, do you have quick connects going to your loader? Raise your bucket and then pop off the disconnects for the raise function (follow hoses from lift cylinders back to QCs). Let the loader sit overnight. If it is on the ground in the morning or significantly lower, then the cylinders are leaky. If it is still in the air, then the joystick valve is leaky and the cylinders are okay.

BTW: All you need is one leaky cylinder to cause the loader to drop. Since the cylinders are in parallel, one bad cylinder will allow fluid from the other good cylinder to bypass and leak down. It is best to replace seals in both cylinders if you end up having them rebuilt.

 

[jinman]

JJ,
Based on the following assumptions the cylinder will move very little or not at all with bad seals.

1) Cylinder is double acting and full of oil.
2) Load is in the direction of forcing the cylinders to retract.
3) No external leakage path from either cylinder port.

Reason being that under these conditions there is more volume in cap end than there is in the rod end. Oil does not compress so there is no room for the oil to transfer from the cap end to the rod end. Cylinder will move until the pressure is equal at both ports and then stop.

Does this make sense?

Roy

No, that is NOT correct. The cylinder will move toward retract until the point that only the difference in cylinder volumes is achieved in the extend side. When the cylinder is fully extended, there is no oil in the retract side because the ram is fully out. As the cylinder tries to retract, fluid leaks around the seal until the retract side is full and only the difference in volume is contained in the extend side. At that point the ram will be 80% to 90% retracted. That's when it will stop because of hydraulic lock.

 

[Leejohn]

Leak down?? If a guy takes a cyl. and take the piston seals off. Fill the cyl full of oil then plug both ends, now add 200 to 300 lbs. to the rod. Well it go in?
Having hard time understanding this, because there is always a load on the cyl until it hits the ground or bottoms out.

 

[J_J]

Not leak out but transfer, from one side of the piston to the other. The weight of the lift arms and bucket and possible load, will affect the rate of decent.

Everyone would like a cyl that would go into hyd lock when the valve spools are closed, but that ain't going to happen. Some cyl and valves are better than others, and that is why there is a leakage rate allowed. If not, they would be replacing valves and cyl all the time.

If this isn't true, just look at all the cyl seals that are replaced and put the loader back in operation. The valve also has a leakage rate.

Some of the seals had cuts, nicks, flatten, extruded, etc, to almost nothing.

 

[redgoldwing]

I'll give that a try Jim. I have the bucket off-loaded right now but will check this the next time I hook up.

Thanks,

Bill Campbell
Pink Ribbon Farm
Oxford, PA

 

[J_J]

Has anyone ever considered the static pressure that is on the spools with or without a load? What we are talking about here is a bucket with a load out on a lift arm, using the lever principle, pushing on the cyl rod with as much as 1000 lbs, plus the mechanical advantage, and we expect the spools to hold the lift arms and tilt cyl in place. Some hyd system can and will hold for weeks or months. It has to be the quality and or the specifications that the products are manufactured..

 

[J_J]

If the valve is in neutral, and if a valve spool is leaking, where does the fluid go? To the OUT port, or to the main gallery/, PB port, or either one.

I would think the main gallery, but could be wrong, and if this is the case, I could just remove the hose off the PB port and the cyl fluid that is leaking, would empty into a container, to prove a point. Do the same thing to the OUT port to check if the fluid is leaking out there.

With a valve spool leaking at a 10 drop per min rate, it would leak 14,400 drops in 24 hours, and with some cyl, they would be on the ground.

A quart contains about 18,896drops, so to leak a quart, it would take about 31 hrs.

This is all about the hyd leak rate and where did the fluid go, and is this unsatisfactory, tolerable or needs repaired.

 

[J_J]

Jim,

[ If it is still in the air, then the joystick valve is leaky and the cylinders are okay.]

In order to test the valve spool, you need some pressure and fluid.

If you pop the QD off the base end, to check if the cyl is leaking, and if the cyl proves good, so although the leaking spool is providing an outlet for the cyl fluid from the rod end, which isn't much, what will happen to all the fluid in the base end. It is closed off by the disconnected QD, and the seals are good. What will allow the cyl to move? The valve is in neutral. I don't see a way for the lift arms to descend.

The way to test for a leaking spool, is to have fluid on the spool from the cyl in the neutral position. If this is true, then both lands of the spool would have to leak to let fluid in one end of the cyl and a way out of the cyl. If only one end of the spool is leaking the cyl might not move.

Maybe AKKAMAAN can explain this better.

 

[oldnslo]

Leak down?? If a guy takes a cyl. and take the piston seals off. Fill the cyl full of oil then plug both ends, now add 200 to 300 lbs. to the rod. Well it go in?
Having hard time understanding this, because there is always a load on the cyl until it hits the ground or bottoms out.

As long as it is a single rod cylinder it will not retract. I know Jinman does not believe this but lets try some volume calculations to see if this helps clear this up.

Cylinder size: 2 inch diameter bore x 1 3/8 inch diameter rod x 10 inch stroke
Blind end area is 3.14 sq inches and volume is 31.4 cubic inches
Rod end area is: 1.66 sq inches and volume is 16.6 cubic inches

Actual cylinder rod area is 1.49 square inches and volume is 14.9 cubic inches

With the cylinder extended there is approximately 14.9 cubic inches more oil in the blind end that will fit in the rod end. Now based on the pricipal that oil and the steel rod do not compress, where is this oil going to go?

NOTE: Areas and volumes are rounded off. That is why there is a 0.1 cubic inch discrepency in volume.

Roy