Double Check Valves: Providing Backup

A control system is a process which consists of control valves, actuators, controllers, and sensors.  The goal of the control system is to provide maximum regulation to the plant operator or plant personnel.  Double check valves provide an essential means of controlling the variables inherent in regulating a control system.

Double check valves are devices that are used to regulate control loops in a process.  One plant may have multiple control loops, which all require control valves to monitor and control the process variable of the particular loop.  Pressure, level, temperature, flow, etc., must all be maintained within specific set parameters in order to ensure a quality end product.  Check valves are used to ensure that the process media in the system flows in the right direction, and they automatically shut when the pressure falls below the cracking point.  The cracking point is the minimum amount of upstream flow pressure required to open the check valve.  Check valves also ensure that downstream flow is virtually impossible, since they are designed to only allow flow in one direction.

Double check valves are comprised of two check valves, assembled next to each other within a pipeline. A check valve is a two-port valve that only allows liquid or gas to flow in one direction. Two-port valves have two openings in the main body of the valve; one is for the entrance of a substance, and one is for the exit. Check valves are available in a variety of sizes and materials, which give company owners the flexibility to select and order the valve that is appropriate for their particular design. Additional, check valves are manufactured for specific amounts of pressure. It is important to consider the pressure that could be exerted in the processes of operation, and then order check valves that are capable of functioning in those conditions.

The most common control valves are sliding-stem globe valves and angle valves.  Other general valve design types include ball, fixed cone, butterfly, gate, check, needle, plug, and spherical.  Each type of valve is designed for a particular application, and these valves are rarely interchangeable. Also, each type of valve can be custom assembled to meet the particular process for which the valve is intended to be used.

Double check valves can fill the need in almost any part of a company’s process control loop.  Other sizes, styles, and constructions of control valves include cage-style valve bodies, disk-stack style valve bodies, angle seat piston valves, single-port valve bodies, balanced-plug cage-style valve bodies, high capacity, cage-guided valve bodies, port-guided single-port valve bodies, double-ported valve bodies, three-way valve bodies, diaphragm valves, rotary valves with butterfly valve bodies, v-notch ball control valve bodies, eccentric-disk control valve bodies, eccentric-plug control valve bodies, sliding cylinder valves with directional control, spool, piston valves, air operated valves, relay valves, or pinch valves.

The regulation of flow must be maintained at a sufficiently linear pace to stay within the specified operating parameters of a process control system.  Double check valves are integral to regulating the control loop, and they directly influence profitability with their performance. Improperly selected valves will prove to be detrimental to the performance of the control loop and safety system.