Here Are 3 Problems and Fixes for Directional Control Valves

Posted by Airmax Pneumatics on September 29th, 2022

Direct Control Valves (DCVs) that don't function correctly can cause problems with a customer's hydraulic system. When the hydraulic system is online, you can troubleshoot some DCV problems on the fly. There are three DCV problems your end-user should watch out for in this article.

DCVs can degrade system performance in many ways. Among the most common problems are sticking/won't shifting, internal leakage, and external leakage.

Problem 1: Sticking/will not shift

The majority of DCV valves have a sliding spool/bore design. When a valve sticks, the spool cannot be moved by applying normal force. This sticking action can be caused by contamination, silting, mechanical failure, or operator error. Here are some of the most common causes.

Contamination

When hard particles get between the bore and the spool, the normal amount of force required to move the spool increases beyond the operator's capabilities.  The spool becomes jammed and cannot move unless the contamination is removed.  When the spool is forced to move, gouges and wear will occur in the bore and spool. A cycle of contamination occurs, which causes increasing damage until the valve leaks excessively. The best way to fix the sticking action is to take apart the valve and remove the contamination before it causes more damage.

Silting

Silting is similar to contamination, but usually involves soft contamination, such as sludge and varnish.  Silting increases the sliding force to move the spool, so the operator cannot generate enough force to move it past the silt in hydrostatic lands and bores.  Cleaning all the parts of the valve is the best way to correct a silting problem.

Mechanical Failure

A DCV has many small parts, some of which are prone to breaking.  It is possible for springs, pins, washers, and detent devices to break and cause the valve to jam or stick.  The broken parts will need to be replaced or the entire valve will need to be replaced.

Operator Failure

For the DCV to change position, some type of external signal is used.  Electrical (solenoids), hydraulic (pistons), mechanical (levers and rods), and pneumatic (pistons) operators are the most common.  The first step is to determine if the sticking action is caused by something inside the hydraulic portion of the DCV or by the operator. In most valve operators, a small mechanical device called a manual override allows the mechanic to manually operate the valve.  More than likely, it is an operator issue if the valve shifts when the manual override is used but not when the normal signal is used. A hydraulic or mechanical problem inside the DCV is likely to cause the valve not to shift when the manual override is applied. If the hydraulic section of the DCV fails, the solenoid coil will burn out and need to be replaced when the valve is disassembled and rebuilt.

Problem 2: High Internal Leakage/Heat

In hydraulic systems that have high levels of contamination, sliding spool valves are more likely to wear.  During wear, more pressurized fluid is lost through these increased clearances and returns to the reservoir without providing any useful service. In the process of moving from high pressure to tank pressure, energy is released as heat. The valve temperature will increase, causing even more leakage. DCVs with high leakage typically have slower cycle times, slower actuator speeds, and drifting or moving actuators when they shouldn't.  In the case of DCVs with high leakage, a complete replacement is the only solution.

Problem 3: External Leakage

There are usually several causes of external leakage in DCVs, including seal failure, spool wear, push pin wear or a failure of the solenoid core tube. When a seal area of an exposed manually operated spool becomes worn or damaged, it cannot be repaired and will have to be replaced. It is possible to replace seals, push pins, and solenoids.  

Conclusion

A properly maintained Directional Control Valve will avoid system contamination. Maintaining clean, cool, and dry hydraulic oil (preventing water contamination) will prevent most DCV failures and prolong their life.

Airmax Pneumatic is a leading 5/2 Way Double Solenoid Valve Manufacturer and Supplier in India.