Sluggish Valve Spool Response

5 Causes Of Sluggish Valve Spool Response And How To Fix Them.

Let’s face it, when your hydraulics don’t work as they should, it’s frustrating.  To help ease your frustrations, here are a few things to check for when your hydraulic valves are sluggish.

Dirt in the system

Hydraulic valves need to be clean in order to operate properly.  Any kind of debris, dust or gunk can spell problems.  This is especially likely if the system was recently repaired due to another component failure. But don’t worry, follow these steps and your hydraulic valve will be good as new.

  1. The first thing you should do is drain the system and flush it to remove as much of the debris as possible.
  2. Then take the valve apart and clean it with a quality, residue-free parts cleaner.
  3. Inspect all parts for wear/scoring/scratches. These allow oil to bypass the valve internals causing excessive pressure drops or excessive back pressure.
  4. Replace any component that has suffered excessive wear.
  5. Check for discoloration. This is an indicator of chemical/heat related issues in the system that must be addressed.
  6. Once it is clean, reassemble the valve and replace all rubber/soft components. They are inexpensive and worth the time now, versus having to take it all apart again later.
  7. Refill the system with new clean fluid. Make sure that you filter the replacement fluid during the transfer process. If you don’t, you will introduce fresh contaminates into your reservoir/system and you’ll be right back at square one.

Restricted drain

Another common cause of sluggish spool response in hydraulic valves is a blocked drain.  To check this, install a pressure gauge and flow meter in the drain/tank port line. All hydraulics work on differential pressure. If back pressure is excessive, the actuation pressure must overcome it first before it can move the spool. Most systems require minimum back/drain pressure to function smoothly. If you have a couple of flow meters available, install one on the inlet of the valve and compare what is going into the valve from what is going out. Excessive outflow indicates too much internal leakage, reducing the fluid available to function the valve. (Please note: this method will not work on valves that have internal drains. The internal drains connect to the tank port and are indistinguishable from normal return flow.)

Low pilot pressure

If your pilot pressure is low, you will have less force to operate the valve properly.  To resolve this, verify that your supply pressure is adequate to your pilot control valve. Most pilot controls draw from system pressure, so supply pressures should be equal to system pressure. Using installed pressure gauges, ensure that pilot pressure from the pilot control is reaching the piloted valve. If not, your pilot control valve needs to be repaired/replaced. (Please note: this process will only work on externally piloted valves. Internally piloted valves do not have test points to verify pressures.)

Solenoid malfunctions

To check your solenoids are working correctly you should first check that you are getting the proper voltage and frequency from the source. If either is faulty, correct. If the power supply is correct, verify the condition of the coil/solenoid. This can be done by simply measuring the resistance of the coil with an Ohmmeter. Based on the wattage of the coil, the voltage available and the current draw of the coil, you can determine the resistance the coils need to have to operate properly. If the resistance is too high or too low, the coil will not energize properly and the valve will not function.  If the resistance is good and the power supply is correct, the problem is internal. Never energize a coil without it being installed on the valve. You could damage the coil.

Distorted valve body

A distorted valve body can also cause sluggish spool response. This is something that would most likely occur after a repair of the valve. To correct this, loosen all of the mounting bolts to relieve tension on the housing. Retighten the bolts in steps of 25% and using a crisscross pattern.  DANGER: remove all system pressure from the circuit before loosening any bolts. Personal Injury or equipment damage could result.

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