What is the Valve Seat Leakage Class for My Valve?

High Pressure Control Valve in a Field

Control Valve Seat Leakage

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.

How many leakage classes are there for valves?

There are actually six different seat leakage classifications as defined by ANSI/FCI 70-2-1976.

But you will likely be concerned with just two of them: Class IV and Class VI.

What is a Class 4 Valve? 

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.

All Kimray High Pressure Control Valves with metal to metal seats are Class IV (4).

What is a Class 6 Valve?

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

All Kimray valves and regulators with resilient seats are Class VI.

Valve Seat Leakage Class

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.


Valve leakage class calculations

The chart below shows the calculations of allowable leakage for Class VI valves at port diameters 1"-6" on, using the standard measurements of ml. per minute and bubbles per minute. 

Allowable Leakage Chart