What is the leakage class for my valve?

A Rule of Thumb

Control valves are designed to throttle, but they are also often expected to provide some type of shut-off capability. A control valve’s ability to shut off has to do with many factors: Balanced or unbalanced plug, seat material, actuator thrust, pressure drop, and the type of fluid can all play a part in how well a particular control valve shuts off.

There are actually six different seat leakage classifications as defined by ANSI/FCI 70-2-1976. But you will be concerned with just two of them: Class IV and Class VI.

Class IV is also known as a Metal To Metal Seat classification. It is the kind of leakage rate you can expect from a valve with a metal plug and metal seat.

Class VI is known as a Soft Seatclassification. Soft Seat Valves are those were either the plug or seat or both are made from some kind of composition material such as Nitrile or Polyurethane.

Two Leakage Classes

Leakage Class Allowable Leakage Valve Types
Class IV 0.01% of rated valve capacity. Intended for
single-port valves
with metal-to-metal
seats.
Class VI The test fluid is air or Nitrogen.
Pressure is the lesser of 50 psig
or operating pressure.
The leakage limit depends on
valve size and ranges from
0.15 to 4.00 ml. per minute
for valve sizes 1 through 6 inches.

Intended for
resilient-seated
valves.

Summary

Leakage Class Valve Types Class IV All Kimray High Pressure Control Valves (motor valves) with metal to metal seats. Class VIAll Kimray valves and regulators with resilient seats.

This includes:
• Regulators
• Low Pressure Control Valves
• Piston Balanced High Pressure Control Valves