Need Some Hydraulic Troubleshooting Help

[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