Check Valve Selection Criteria

Careful consideration of check valve selection criteria is vital in maintaining the integrity of piping system equipment. They are practical, easy to install, cost-effective, and can be used in a variety of applications and working conditions. However, all these benefits will not be available if the wrong valve is selected for an application. Proper selection is also crucial to saving costs. A number of factors must be considered before selecting a check valve.

What are check valves?

Check valves are fluid control devices that restrict the flow of media in a piping system to one direction. The function of the valve is broadly defined and plays different roles in different industries. Also known as one-way valves or backflow preventers, check valves prevent the flowing media from flowing backward. You can read more about check valves and their uses in this article.

How Check Valves Work

A check valve consists of two ports – an inlet and an outlet – and an opening/closing mechanism. The unique feature of check valves that distinguishes them from other types of valves such as ball and butterfly valves is that unlike these valves which require some form of actuation to operate, check valves are self-operating. Check valves operate automatically. They rely on differential pressure to effect control. In their default position, check valves are closed. When media flows from the inlet port, its pressure opens the closing mechanism. When the inflow pressure drops below the outflow pressure due to a stoppage of flow, or the pressure on the outlet side becomes greater for any reason, the closing mechanism immediately closes the valve.

The closing mechanism in check valves is usually held in place by a spring-loaded, counterweight, or gravity. To open the valve, the media must overcome the force of the spring or closing mechanism.

Check valves do not operate based on differential pressure alone. If this were the case, dripping would be sufficient to open the valve. Therefore, a specified minimum pressure is required to open the check valve. This is known as the cracking pressure. The cracking pressure of a check valve is the minimum specified inlet pressure required to open the valve, sufficient to allow detectable flow.

Check Valve Selection Criteria

These valves are vital in maintaining the integrity of piping system equipment. They are practical, easy to install, cost effective and can be used in a variety of applications and operating conditions. However, all of these benefits will not be available if the wrong valve is selected for an application. Proper selection is also critical to cost savings. The following factors should be considered before selecting a valve:

Application

A check valve can be used in wastewater, chemical or water treatment plants, among other applications. The application determines the design and method of operation of the selected valve. For example, ball valves are suitable for wastewater treatment because they do not interfere with flow. However, they perform poorly in chemical mixing applications due to slow closing speeds.

Cracking pressure or minimum operating pressure

It is essential to install a properly sized check valve with the appropriate cracking pressure. If the cracking pressure in the valve is excessive, the flowing media may not be able to open it. On the other hand, a check valve will not function if the cracking pressure is insufficient.

Size

Valves come in many sizes. Of course, the size of the check valve selected must match the sizes of the pipes and other associated equipment.

Direction

A check valve is designed to be installed vertically or horizontally and cannot be installed in an orientation other than the intended one. Pay attention to the installation required by your piping system before selecting a valve.

Material

The material of the valve, whether the valve body or seat, must be compatible with the flowing media. It can be made of wrought iron, stainless steel, brass, polypropylene, polyvinyl chloride, etc., and material compatibility is vital.

Operating Conditions (Temperature, Pressure, Humidity, etc.)

Different types and materials of check valves are designed for different levels of operating pressure, temperature, and flow velocity. Careful consideration of these factors is critical to selecting the correct type of valve.

Cost

Initial purchase, assembly, maintenance, and operating costs should be considered before selecting a check valve. Cost is usually an important consideration, coming after quality and function. However, note that low purchase costs can result in high operating/maintenance costs. A cheap check valve that fails to perform its function can cause serious problems in the pumping station. Some check valves may require expensive pipeline modifications, which increases assembly costs. In terms of maintenance costs, the more complex the valve, the more expensive it is to maintain and repair. Some complex solutions require professional assistance from the supplier.