Understanding Check Valves: Sizing for the Application, Not the Line Size
Often misunderstood and frustrating to understand, check valves are one of the least popular gadgets in the flow control industry. However, like most highly technical components, understanding a check valve’s application and installation process is a crucial part in building a successful system.Check Valve
What is a check valve supposed to do?
Fully understanding the function of a check valve serves as the first step toward harmony between machine, man and valve.
A check valve simply allows flow in one direction and prevents back flow when a fluid line changes direction. The beauty of the device and the reason their use is so widespread lies within their self-automation. Check valves will continue to operate even if the system loses air pressure, power or if a human intervention causes a system shutdown.
This hands-free capability demonstrates why check valves are used everywhere, including in your home’s sump pump.
The application matters most
As the title above indicates, the most critical factor when using any check valve is the application, not the size of the line. In other words, what task will this check valve be expected to perform and in what environment?check valve
If a valve is not operating in optimal fashion, its service life may be shortened and your system will not operate efficiently. Speaking in terms of internal components, you want the disc to be stable against the internal stop when the valve is open or closed completely. If this doesn’t happen, the disc inside the mechanism will flutter.
This mistake generally occurs when a check valve is selected using the same criteria as an on/off valve. However, a check valve operates solely on flow conditions, unlike on/off valves that are manually or electronically controlled. The check valve disc is always in the flow stream.
Installing a valve with too much resistance to the flow will cause fluttering. Like any working metal component, more fluttering means more movement, and that means more wear and a shorter service life for the valve. Think of it like the door on your house. If you only open it at the beginning of the day and at the end, it will last longer. If the door is constantly opened and closed, the pins and hinges will fail faster.
In more severe cases, pieces of that misfit valve could break loose and run through system lines, eventually leading to a costly failure.
Picking the right valve
Sufficient pressure should exist within the line to fully open a valve. If the flow is not sufficient enough to create a full opening, the pressure drop within the line will be too great. In this case, a large-rated Cv becomes a detriment to the valve (unlike typical on/off valves). Understand the pressure and the exact job you want the valve to perform. But most importantly, think application, not size, before adding a check valve.