If you take the time to properly design and configure your high-pressure water hydraulic system, then valve leakage should be minimal. The first step to managing this issue is understanding the difference between internal and external leaks. Some leakage may be inevitable and tolerable within a descale valve system.
How do you determine how much valve leakage is tolerable? This will vary by facility and application. For example, an acceptable amount in a forging operation would be unacceptable in a food processing plant. Systems that manufacture commodity items can tolerate more than systems that produce high-cost components.
To establish acceptable parameters for high-pressure hydraulic valve leakage, review the following industry standards that were created for different types of valves:
Manufacturers Standard Society (MSS) Standard SP-61: Establishes allowable leakage in valves that operate as isolation or check valves.
American National Standards Institute (ANSI) Standard 70-2: Sets different leakage classifications for control valves, ranging from Class I (unspecified amount of leakage) to Class V (zero leakage).
Note: The above standards were developed to establish guidelines for valve manufacturers to use during industrial valve design. But, these standards use a set of specific operating parameters, such as viscosity, pressure and temperature, when measuring leakage.
Proper Valve Leakage Testing
Industry guidelines can be helpful in the descale valve selection process. But, they do not provide any guarantees for how a particular valve will operate in service conditions where the actual operating parameters can exceed those set forth in the testing protocol of a particular standard. If you need a zero-leakage valve, don’t assume that you can select an ANSI Class V valve out of a catalog and be good to go. The valve should be tested under actual service conditions to verify that it will provide the required control.