Throttle Valve

By reducing the pipe cross-section, a throttle creates a local flow resistance that the flowing fluid must overcome. Before the constriction, the flowing medium builds up, so that the pressure before the throttle valve is higher than behind the throttle. The higher the pressure difference between the inlet and outlet pressure, the higher the volume flow through the throttle.

Throttle Valve – Design

The throttled portion of the volume flow is discharged from the pressurized circuit by a valve (the so-called pressure relief valve). This results in high power losses. Depending on the application, the design of an expansion valve can be simple or complex. A simple throttle merely represents a constriction in the line. A complex throttle valve, for example, has a control system.

A throttle check valve allows the flowing fluid or gas to flow back unthrottled in the opposite direction to the flow direction of the circuit, in addition to throttling. This is made possible by an additional check valve, which only opens in one flow direction. If the medium flows in the opposite direction of the check valve, it closes, and the medium is forced to pass through the throttle. This reduces the flow rate.

A throttle check valve is used in hydraulics, for example, to regulate the speed of a piston’s movement. With incompressible hydraulic oil, the inflow and outflow are regulated so that both the extension and retraction of the cylinder can be regulated independently.

Throttle Valve – Types

The cross-sectional constriction within the throttle valve can be fixed or adjustable. If the flow diameter is variable, it is an adjustable throttle valve. In controlled throttles, the cross-section is determined by a control variable.

If it is merely a static reduction of the flow diameter, the valve is called uncontrolled. Optimal adaptation to the respective application is achieved by varying the different sizes (e.g., length and diameter) of the throttle valve.

Distinction between Throttle Valve and Orifice

In contrast to an orifice, the length-to-flow diameter ratio is significantly larger in a throttle. If the volume flow increases, the pressure difference before and after an orifice remains constant from a certain volume flow value, whereas with a throttle, the pressure difference is proportional to the volume flow.