# Valve Characteristics

## Kv, Kvs and characteristic of a valve

The flow coefficient Kv of a valve or fitting in a certain position represents the water flow rate that goes through it under a differential pressure of 1 bar.

The Kvs of a valve is the particular Kv value, when the valve is fully open.

The relationship between the valve travel and the Kv at every position is the valve characteristic.

## Fast opening characteristic

The fast opening characteristic is not normalized. It is the characteristic generated by a globe valve, with a flat plug. It is usually only used on On/Off valves. A slight alteration of it might be used in the self-acting valves (pressure reducing valve or thermostatic valves).

## Linear characteristic

The Kv of the valve at a certain position (hence the flow rate going through it) is directly proportional to the valve travel. This characteristic is popular in flow control applications.

## Equal percentage characteristic (=%, or Exponential)

Any change in the opening from its current position changes the Kv by the same percentage of its current value at current opening. This characteristic is defined with a rangeability R, which is the ratio between the Kvs of the valve and its minimum controllable Kv. R is typically between 30 and 50.

The relation between Kv and Kvs is as follows:

Kv = Kvs.R – %travel/100 – 1