Four functions of valves

By "Apollo" Valves
February 19, 2019

From manufacturing equipment to chemicals processing, and within every home and business that receives natural gas, electricity, and drinking water, valves are the nuts and bolts of piping systems that provide for the flow of liquids, gases, or granulated solids.

The human heart employs a type of mechanical valve to make sure blood flows in one direction - otherwise it would be difficult for the entire body to receive oxygen-rich blood. In this same way, processes require a controlled and often one-way flow of ingredients for the sake of product delivery and to maintain appropriate levels of pressure, temperature, and contents within a closed system.

This is the basic job of mechanical valves - to use one or more of the four valve functions to control the flow and the pressure of mechanical systems. While there are many types of valves, they perform four main functions.

1. Control valves for process regulation

Historically, valves were designed to stop the flow within piping systems. But today, regulating valves go beyond this simple concept to throttle the flow by making slight adjustments depending on what the system demands. When a process system demands a specific amount of flow, temperature, level, or pressure, it is the job of a regulating valve to control that process variable.

Often it is a flexible diaphragm within the valve body that will push toward an outlet that is fitted with a measuring gauge. When the setpoint limits are met, this diaphragm expands or contracts to close or open the inlet to the valve body - successfully regulating that process variable. Examples of regulating valves include diaphragm and butterfly valves.

2. Isolation valves for system maintenance

Isolation valves are used to fully cut off the flow of fluids or gases - often for the purpose of system maintenance and repair or for safety in the case of a chemical leak, for example. But isolation valves also can be used when the flow path of a closed system needs to be redirected, especially in batch or continuous processing.

Many types of valves can serve to isolate or redirect a piping loop, but close attention to the valve’s performance under the shut-down pressures and temperatures along with strong piping connections will make some valves a better choice than others for the purpose of isolation. These include pinch, gate, and plug valves.

3. Non-return valves for preventing flow reversal

The closest analogy to valves in the human heart would be the two-port check valve - a non-return valve that only allows flow in one direction. Any back flow or back pressure will seal the valve inlet shut. Check valves have many applications, with the obvious being to protect the integrity of process ingredients.

Swing-check valves are installed in sewage systems to prevent flooding, and ball-check valves are common in consumer products such as spray or pump dispensers.

4. Special purpose valves for unique applications

Multi-port valves and hybrid combinations of other valves are classified as special purpose. These valves are designed and manufactured to meet the challenges of complex piping systems, including high-pressure applications, space craft, nuclear energy, agricultural irrigation, and cryogenics technology.

If a process or mechanical system requires an uncommon material or very precise operating parameters that standard valves cannot meet, a special purpose valve can be designed to meet exacting specifications. Relief valves will fall under this designation.

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