What Is an Orifice in Flow Control Valves?

Flow control valves come in two types: viscosity-dependent and viscosity-independent. Those that are not viscosity-dependent are called an orifice. Flow control creates resistance in a hydraulic system.

A 2-way flow control valve consists of two control elements: one is a viscosity-independent restrictor (orifice), and the other is an automatic restrictor that performs the regulating function.

The regulating cross-section is changed via the pressures acting on the automatic restrictor element. The automatic restrictor element referred to here can also be called a pressure compensator. These valves are symbolized with the symbol for an adjustable flow control valve together with a rectangle enclosing an arrow representing the pressure compensator.

The diagonal arrow symbol on the valve indicates that the valve is adjustable.

Definition of an Orifice

An orifice is a small opening, of fixed or variable diameter, that creates a pressure drop by restricting fluid flow.

Use of a Fixed Orifice

Fixed orifices are preferred for simple, low-cost flow-restriction applications.

Flow Rate-Pressure Relationship

The fluid flow rate through an orifice varies in proportion to the square root of the pressure difference across the orifice.

Related Questions

Since the orifice narrows the path the fluid passes through, the fluid experiences a pressure loss as it passes through. This pressure drop creates controlled resistance in the system, limiting the amount of flow.

According to the rules of fluid dynamics, the velocity of a fluid passing through a narrow opening increases in proportion to the square root of the pressure difference. This physical relationship causes the flow rate through the orifice to vary as the square root of pressure, not linearly.