Flow valve with fixed or adjustable throttling cross-section. Its flow is dependent on the pressure difference at the throttle: the smaller the pressure differenceΔp between the (constant) inlet pressure p 1 and the (variable) outlet pressure (load pressure) p L, the lower the flow. With a constant inlet pressure and variable load pressures, it is not possible to achieve a constant flow rate. It is only in the case of a constant pressure drop (at constant oil viscosity) that a constant flow rate is created at a throttle. As a result, load-independent flow cannot be achieved with a throttle valve. As the throttle valve does not have a return connection, the portion of the flow rate removed by the throttle can only be removed from the circuit via the system's pressure-limiting valve. As this valve is set to the nominal pressure p N, there are relatively high power losses (see control with throttle).
Figure D 49: Pressure-velocity curve on a throttle valve