3 Directional Control Valve Problems & Fixes

Malfunctioning Direct Control Valves (DCVs) can cause problems in your customer's hydraulic system. You can quickly fix some DCV problems when the hydraulics are online. This article provides information on 3 DCV-related issues that the end user should be aware of.

There are many ways DCVs can reduce system performance. The most common are sticky/non-slip, internal leaks, and external leaks.

Problem #1: sticks/doesn't convert

Most DCV valves use a sliding spool/bore design. When the valve is stuck, the spool cannot change its positions when the actuator is using normal force. Various factors can cause this sticking, including contamination, sediment, mechanical failure, or actuator failure. Let's take a look at these common causes.

radioactive contamination

When solid particulate contamination occurs between the orifice and the spool, the normal amount of force required to move the spool increases beyond the limits of the actuator. The spool gets stuck and will not move unless the contamination is removed. Forcing the spool to move will damage the bore and spool, causing pitting and wear. This creates a cycle of contamination, increasing damage until the valve begins to leak excessively. Disassembling the valve and removing contamination before it causes further damage is the best way to repair sticking motion.

Malfunctioning Direct Control Valves (DCVs) can cause problems in your customer's hydraulic system. You can quickly fix some DCV problems when the hydraulics are online. This article provides information on 3 DCV-related issues that the end user should be aware with the help of Rexroth valve.

There are many ways DCVs can reduce system performance. The most common are sticky/non-slip, internal leaks, and external leaks.

Problem #1: sticks/doesn't convert

Most DCV valves use a sliding spool/bore design. When the valve is stuck, the spool cannot change its positions when the actuator is using normal force. Various factors can cause this sticking, including contamination, sediment, mechanical failure, or actuator failure. Let's take a look at these common causes.

radioactive contamination

When solid particulate contamination occurs between the orifice and the spool, the normal amount of force required to move the spool increases beyond the limits of the actuator. The spool gets stuck and will not move unless the contamination is removed. Forcing the spool to move will damage the bore and spool, causing pitting and wear. This creates a cycle of contamination, increasing damage until the valve begins to leak excessively. Disassembling the Rexroth valve and removing contamination before it causes further damage is the best way to repair sticking motion.

silt

Slime is similar to pollution, but generally includes fine pollution such as mud and varnish. The silt causes too much sliding force to move the pulley and the actuator does not generate enough force to move it through the silt into hydrostatic soils and pores. Disassembling the valve and cleaning all parts is the best way to correct sediment movement.

mechanical failure

There are many small parts inside the DCV and some of them are prone to breaking. Springs, bolts, washers, and disconnects can break and cause the valve to stick or stick. It will require replacement of broken parts or a complete valve.

launcher failed

DCV uses some kind of external signal to make it change position. The most common types of actuators are electric (solenoids), hydraulic (pistons), mechanical (jacks and rods), and pneumatic (pistons). The first thing to determine is if the sticking action is caused by something within the hydraulics of the DCV or the actuator. Most valve operators have a small mechanical device called a manual bypass so that the mechanic can manually operate the valve. If the valve turns when manual override is used but not when normal indication is used, it is most likely an actuator problem. If the valve does not turn when manual override is used, the problem is most likely a hydraulic or mechanical issue within the DCV. Failure of the hydraulic section of the valve can cause the solenoid coil to burn out, which will need to be corrected when the DCV is disassembled and rebuilt.

Problem #2: High Internal Leakage/Heat

Slide spool valves are susceptible to wear, especially in hydraulic systems with high levels of contamination. As the spool and orifice wear, more pressurized fluid is lost through these increased clearances to return to the tank without providing any useful work. The energy generated by going from high pressure to tank pressure is released as heat. As the valve gets hotter it will cause more leaks. The most common symptoms of high leakage in DCVs are slow cycle times, slower actuator speeds, and actuators drifting or moving when they shouldn't be moving. The only solution for heavily leaking DCVs is complete replacement.

Problem #3: External Leak

External leaks in DCVs are usually caused by seal failure, pulley wear, retaining pin wear, or solenoid tube failure. The seals, push pins, and solenoids can be replaced, but if the manual override pulley sealing area becomes worn or damaged, it cannot be repaired and will need to be replaced.

conclusion

The best way to prevent directional control valve failure is to prevent system contamination. Keeping the oil clean, fresh, and dry (preventing water contamination) will prevent most DCV failures and improve the longevity of the DCVs in the hydraulic system.Slime is similar to pollution, but generally includes fine pollution such as mud and varnish. The silt causes too much sliding force to move the pulley and the actuator does not generate enough force to move it through the silt into hydrostatic soils and pores. Disassembling the valve and cleaning all parts is the best way to correct sediment movement.

mechanical failure

There are many small parts inside the DCV and some of them are prone to breaking. Springs, bolts, washers, and disconnects can break and cause the valve to stick or stick. It will require replacement of broken parts or a complete valve.

launcher failed

DCV uses some kind of external signal to make it change position. The most common types of actuators are electric (solenoids), hydraulic (pistons), mechanical (jacks and rods), and pneumatic (pistons). The first thing to determine is if the sticking action is caused by something within the hydraulics of the DCV or the actuator. Most valve operators have a small mechanical device called a manual bypass so that the mechanic can manually operate the valve. If the valve turns when manual override is used but not when normal indication is used, it is most likely an actuator problem. If the valve does not turn when manual override is used, the problem is most likely a hydraulic or mechanical issue within the DCV. Failure of the hydraulic section of the valve can cause the solenoid coil to burn out, which will need to be corrected when the DCV is disassembled and rebuilt.

Problem #2: High Internal Leakage/Heat

Slide spool valves are susceptible to wear, especially in hydraulic systems with high levels of contamination. As the spool and orifice wear, more pressurized fluid is lost through these increased clearances to return to the tank without providing any useful work. The energy generated by going from high pressure to tank pressure is released as heat. As the valve gets hotter it will cause more leaks. The most common symptoms of high leakage in DCVs are slow cycle times, slower actuator speeds, and actuators drifting or moving when they shouldn't be moving. The only solution for heavily leaking DCVs is complete replacement.

Problem #3: External Leak

External leaks in DCVs are usually caused by seal failure, pulley wear, retaining pin wear, or solenoid tube failure. The seals, push pins, and solenoids can be replaced, but if the manual override pulley sealing area becomes worn or damaged, it cannot be repaired and will need to be replaced.

conclusion

The best way to prevent directional control valve failure is to prevent system contamination. Keeping the oil clean, fresh, and dry (preventing water contamination) will prevent most DCV failures and improve the longevity of the DCVs in the hydraulic system.

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