Pressure losses in valves and fittings

Pressure losses in shut-off valves and fittings

Shut-off valves and fittings are used as components for shutting off the flow in pipe systems. The main types of shut-off valves and fittings include valves, taps and gate valves. The closing mechanism is implemented in different ways depending on the design of the valve. When flow passes through the various valves, different pressure losses occur depending on the geometry and open condition of the valve. Pressure losses occur even in the fully open state, as a result of the often sharp defl ection of the flow within the valve. The pressure difference in this case can be expressed by the resistance coefficient Zeta for the open state.

Pressure losses in control valves and fittings

The flow through a flow control valve can be adjusted thanks to the design of the valve. The flow rate at the respective open state is characterised by the valve characteristic. When selecting valves, the flow coeffi cient Kvs at 100% open provided by the valve manufacturer is given. This flow coefficient is a measure of the maximum possible throughput of a fluid through a valve. For valve openings smaller than 100% the flow coeffi cient is called Kv. The flow coeffi cient Kv is between 0 and the Kvs.

The flow coefficient Kv for valves is determined for different opening states via the flow rate Q and the pressure difference Δp between inlet and outlet of the valve.