How does one choose between regulators and control valves?



How does one choose between regulators and control valves?

Many application in pressure control can be handled with either a regulator or a control valve. Particularly in the smaller sizes, regulators usually cost less than a combination of control valves, transmitters and controllers. They are less expensive to buy, install and maintain. But when the application requires a larger valve, the economics begins to change in favour of control valves.

Regulators have a built-in controller and do not require an air supply. This results in saving on purchase and installation cost. And regulators are not subject to air supply failure because the power to operate them is contained in the process fluid. In critical fail safe applications or at locations remote from a source of compressed air, this is an important consideration. However, diaphragm failure in a regulator usually causes valve opening, which can be unsafe.

Regulators versus control valves

Control valves are used with an external controller. This controller has the flexibility of being provided with one-two or three mode control and with remote or manual operations. Materials of construction of the valve include any castable metal and the valve may be lined. Control valves can be made to fail in any position. Valve accessories include positioners limit switches, manual handwheels, solenoids and local controllers. These can be specified to be interchangeable with accessories on valves in other services, resulting in reduced spare-parts requirements.

The setpoint of a regulator is provided integrally, and remote control is usually not possible. As noted earlier, the controller is single mode (proportional only), therefore it suffers from having a setpoint droop curve that varies with throughput. Materials of construction are limited, as is interchangeable with other services. Accessories are not available.

Control valves with controllers and transmitters are more expensive to purchase, install and maintain than are regulators. The control valves are generally larger, requiring more space for installation and making handling more difficult. They required compressed air supplies, which results in increased-cost and increased maintenance.