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Frequently Asked Questions - Loader Valve

Q: I’m having trouble with my tractor loader, how can I determine what the problem is?
A: Below is a loader drift test along with some information on loader valve trouble shooting..

FIELD LOADER DRIFT DOWN TESTS
1) Observe all safety precautions. Do not loosen pressurized lines. Stay dear of loaded members of front end loader. Only an experienced hydraulic technician should work on the system.

2) Make sure all fittings are tight and not leaking. Make sure that there is no external leakage from the valve or cylinders.

3) Make sure that there is adequate hydraulic fluid in the reservoir.

4) With the boom and bucket positioned so that there is no pressure in the hydraulic lines, tee a pressure gage into the rod end hydraulic line on the boom cylinders and a second pressure gage into the base end hydraulic line on the boom cylinders.

5) Cycle the boom cylinders to full extend and then full retract a minimum of 5 times to expel any air in the system. The cylinders should be cycled with the engine near maximum rpm. The bucket should not be loaded during cycling.

6) Leakage test for the boom cylinders/spool.

Place a load in the bucket that induces a pressure reading in the boom cylinder base end of approximately 1000 psi. Raise to approximately mid-stroke. After a short period of time note the pressure on the rod end side of the boom cylinders. It should be near zero and not increasing. If it is not near zero or is increasing, oil is leaking past one or both of the boom cylinder piston seals and the cylinders need to be repaired or replaced.

7) If the boom rod end pressure remains low, use a marking pen to mark a line on the cylinder rod 10 inches away from the cylinder gland.
After a set period of time measure the distance between the line and the gland and subtract the distance from 10 to determine how much the cylinder has retracted. Using the boom cylinder bore diameter, calculate the area of the bore in square inches. Take the area of the bore times the number of inches the cylinder has retracted and divide this product by the time between measurements to determine the leakage rate per cylinder in ins/min. Since there are two cylinders, take this number times two for the leakage rate of the boom spool of the valve. Contact the factory to see if this rate exceeds the allowable rate.

8) Leakage test for the bucket cylinders/spool.

With the boom and bucket positioned so that there is no pressure in the hydraulic lines, tee a pressure gage into the rod end hydraulic line on the bucket cylinders. Cycle the bucket cylinders to full extend and then full retract a minimum of 5 times to expel any air in the system. The cylinders should be cycled with the engine near maximum rpm. The bucket should not be loaded during cycling.

9) With the bucket on the ground, roll the bucket down slightly, pressurizing the base end of the bucket cylinder and reducing the weight on the front tires of the tractor.

After a short period of time note the pressure on the rod end side of the bucket cylinders. It should be near zero and not increasing. If it is not near zero or is increasing, oil is leaking past one or both of the bucket cylinder piston seals and the cylinders need to be repaired or replaced.

10) If the bucket rod end presure remains low check for bucket spool leakage in the valve.

With the bucket lip approximately level and on the ground, place a load in the bucket and raise the boom slightly off the ground. The load should be adjusted so that there is a bucket cylinder rod end pressure reading of approximately 1000 psi. Place a mark on the cylinder rod 1 inch away from the cylinder gland. After a set period of time measure the distance from the gland to the mark and subtract 1 inch to determine how much the cylinder has extended. Using the bucket cylinder rod diameter, calculate the area of the rod in square inches and, using the bucket cylinder bore diameter, calculate the area of the bore then subtract the rod area. Take the result of the subtraction times the number of inches the cylinder has extended and divide this product by the time between measurements to determine the leakage rate per cylinder in in3/min. If there are two cylinders, take this number times two for the leakage rate of the bucket spool of the valve. Contact the factory to see if this rate exceeds the allowable rate.



LOADER VALVE TROUBLE SHOOTING
1) External Leakage
Clean all dirt and oil off the exterior of the valve. Cycle the valve a few times to determine the source of the oil leak.
A. If the external leakage is coming from the ports, remove the fitting, check for any damage to the spot face sealing surface or contamination. Replace fitting sealing washer and torque fitting to proper torque.
B. If external leakage is coming out from the spools on the handle end of the body or is coming out from the spring end caps, replace the spool oring seals as outlined in the valve assembly breakdown.

2) When moving the control lever to move a cylinder, the cylinder moves in the opposite direction before moving in the correct direction.
A. Air in the cylinders. With the bucket unloaded, cycle the cylinders to full extend and to full retract a number of times. This should be done with the engine near maximum rpm.
B. Load check not functioning. With the boom and the bucket on the ground and the engine off, use the handle to move the spools in then out. Remove the load check plug, spring and poppet. Inspect the seat and the poppet for any damage. Inspect for any contamination in the cavity.

3) Loader won't lift the load or is slow.
A. Load exceeds the capacity of loader. Reduce load.
B. Pressure setting of the relief is incorrect. Adjust relief per tractor recommendations.
C. Pump is not functioning correctly.
D. Spools in valve are not being fully shifted — check linkages on joystick.

4) System runs hot.
Check to see if oil is going over relief valve during use of the loader.

5) During use, cylinders become "spongy" or allow some spring like movement.
A. Air in the cylinders. The air can be purged by cycling the cylinders to full extend and to full retract a number of times. This should be done with the engine near maximum rpm and with the bucket unloaded. The reservoir should also be checked to see that there is adequate hydraulic oil.
B.Cavitation. When lowering the boom or rolling out the bucket when it is loaded, the oil supply may not be adequate to keep up with the cylinder movement. The engine may need to be run at a higher rpm or one way restrictors may be needed in the boom base end hydraulic line or the bucket rod end hydraulic line.