Hydraulic Valve Troubleshooting

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Listed below are areas that you can diagnose in hydraulic valves. When working on a specific machine, refer to a machine’s technical manual for more information.

a. Pressure-Control Valves. The following lists information when troubleshooting relief, pressure-reducing, pressure sequence, and unloading valves:

(1) Relief Valves. Consider the following when troubleshooting relief valves because they have low or erratic pressure:

• Adjustment is incorrect.
• Dirt, chip, or burrs are holding the valve partially open.
• Poppets or seats are worn or damaged.
• Valve piston in the main body is sticking.
• Spring is weak.
• Spring ends are damaged.
• Valve in the body or on the seat is cocking.
Orifice or balance hold is blocked.

Consider the following when troubleshooting relief valves because they have no pressure:

• Orifice or balance hole is plugged.
Poppet does not seat.
• Valve has a loose fit.
• Valve in the body or the cover binds.
• Spring is broken.
• Dirt, chip, or burrs are holding the valve partially open.
• Poppet or seat is worn or damaged.
• Valve in the body or on the seat is cocking.

Consider the following when troubleshooting relief valves because they have excessive noise or chatter:

• Oil viscosity is too high.
• Poppet or seat is faulty or worn.
• Line pressure has excessive return.
• Pressure setting is too close to that of another valve in the circuit.
• An improper spring is used behind the valve.

Consider the following when troubleshooting relief valves because you cannot adjust them properly without getting excessive system pressure:

• Spring is broken.
• Spring is fatigued.
• Valve has an improper spring.
• Drain line is restricted.

Consider the following when troubleshooting relief valves because they might be overheating the system:

• Operation is continuous at the relief setting.
• Oil viscosity is too high.
• Valve seat is leaking.

(2) Pressure-Reducing Valves. Consider the following when troubleshooting pressure reducing valves because they have erratic pressure:

• Dirt is in the oil.
• Poppet or seat is worn.
• Orifice or balance hole is restricted.
• Valve spool binds in the body.
• Drain line is not open freely to a reservoir.
• Spring ends are not square.
• Valve has an improper spring.
• Spring is fatigued.
• Valve needs an adjustment.
• Spool bore is worn.

(3) Pressure-Sequence Valves. Consider the following when troubleshooting pressure sequence valves because the valve is not functioning properly:

• Installation was improper.
• Adjustment was improper.
• Spring is broken.
• Foreign matter is on a plunger seat or in the orifices.
• Gasket is leaky or blown.
• Drain line is plugged.
• Valve covers are not tightened properly or are installed wrong.
• Valve plunger is worn or scored.
• Valve-stem seat is worn or scored.
• Orifices are too large, which causes a jerky operation.
• Binding occurs because moving parts are coated with oil impurities (due to overheating or using improper oil).

Consider the following when troubleshooting pressure-sequence valves because there is a premature movement to the secondary operation:

• Valve setting is too low.
• An excessive load is on a primary cylinder.
• A high inertia load is on a primary cylinder.

Consider the following when troubleshooting pressure-sequence valves because there is no movement or the secondary operation is slow:

• Valve setting is too high.
• Relief-valve setting is too close to that of a sequence valve.
• Valve spool binds in the body.

(4) Unloading Valves. Consider the following when troubleshooting these valves because a valve fails to completely unload a pump:

• Valve setting is too high.
• Pump does not build up to the unloading valve pressure.
• Valve spool binds in the body.

b. Directional-Control Valves. Directional-control valves include spool, rotary, and check valves. Consider the following when troubleshooting these valves because there is faulty or incomplete shifting:

• Control linkage is worn or is binding.
• Pilot pressure is insufficient.
Solenoid is burned out or faulty.
• Centering spring is defective.
• Spool adjustment is improper.

Consider the following when troubleshooting directional-control valves because the actuating cylinder creeps or drifts:

• Valve spool is not centering properly.
• Valve spool is not shifted completely.
• Valve-spool body is worn.
• Leakage occurs past the piston in a cylinder.
• Valve seats are leaking.

Consider the following when troubleshooting directional-control valves because a cylinder load drops with the spool in the centered position:

• Lines from the valve housing are loose.
O-rings on lockout springs or plugs are leaking.
• Lockout spring is broken.
• Relief valves are leaking.

Consider the following when troubleshooting directional-control valves because a cylinder load drops slightly when it is raised:

• Check-valve spring or seat is defective.
• Spool valve’s position is adjusted improperly.

Consider the following when troubleshooting directional-control valves because the oil heats (closed-center systems):

• Valve seat leaks (pressure or return circuit).
• Valves are not adjusted properly.

c. Volume-Control Valves. Volume-control valves include flow-control and flow-divider valves. Consider the following when troubleshooting these valves because there are variations in flow:

• Valve spool binds in the body.
• Cylinder or motor leaks.
• Oil viscosity is too high.
• Pressure drop is insufficient across a valve.
• Oil is dirty.

Consider the following when troubleshooting volume-control valves because of erratic pressure:

• Valve’s poppet or seat is worn.
• Oil is dirty.

Consider the following when troubleshooting volume-control valves because of improper flow:

• Valve was not adjusted properly.
• Valve-piston travel is restricted.
• Passages or orifice is restricted.
• Valve piston is cocked.
• Relief valves leak.
• Oil is too hot.

Consider the following when troubleshooting volume-control valves because the oil heats:

• Pump speed is improper.
• Hydraulic functions are holding in relief.
• Connections are incorrect.

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