Troubleshooting Valves

from sweethaven
Posted 5/31/2004

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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