This is self-explanitory, the valve has a leak, due to some fault of the valve or operation out side of the valve’s parameters it allows for the release of process fluids. Leaks usually eminate from either the base of the stem as it enters the valve body, or it ma leak internally at the valve seat.
In some instances the valve may not be designed to close 100%, as such this must be taken into consideration when determining the amount of valve leakage. Valve leakage is classified into 6 different classes (I-VI)
| Class | Max. Allowable | Test Medium |
| I | – | – |
| II | 0.5% of rated capacity | Air or Water |
| III | 0.1% of rated capacity | Air or Water |
| IV | 0.01% of rated capacity | Air or Water |
| V | 0.0005mL/min of water per ins. of port dia. per psi differentioal | Water |
| VI | Not exceed amount above | Air or Nitrogen |
Effective monitoring and maintenance of the valve will prolong life and prevent and mitigate problems. Key to good maintenance is record keeping and logging of previous and future work to be done on said valves. Added to that would be the willingness to make the obvious repairs upfront.
Leaks may be inenvitable during the life span of a valve, they are the result of operation and general wear and tear on the equipment. The valve components are machine components, in motion and subject to forces and erosion like any other, as such it must be properly maintained and components must be replaced according to specification or manufacturer guidelines.
