Which Spring Is Right for Your Check Valve? Our Video Explains It
by Luke Wurban, on Thu, Apr 25, 2019 @ 11:04 AM
The significance of cracking pressure, resealing pressure and back pressure
In this short Tech Tip video, Swagelok's product experts explain the relevance of choosing the proper check valve and the cracking pressure in which you get the first indication of flow. If you need more information, please message us below.
In a check valve, the stiffness of the internal spring decides when the valve will open and when it will reseal. Picking the right spring makes all the difference in getting the performance you desire.
We start with the term "cracking pressure," which is when you first get an indication of flow when opening the valve, such as a stream of bubbles. The other key term is "resealing pressure," is when the valve closes to the point where there is no indication of flow. A check valve usually needs some back pressure to seal properly.
Several factors can influence resealing pressure. First there's the pressure and temperature of the fluid. Then there's the pressure and temperature of the environment. Third is the design of the check valve. (Some check valves have the poppet independent of the O-ring. Other check valve designs have the poppet and O-ring bonded together.)
It's also important to note the speed at which the back pressure builds up. Applications with a faster back-pressure buildup will reseal at a lower resealing pressure. Applications with slower buildup of back pressure may require higher back pressure in order to reseal.
To aid in preventing backflow, check valves are frequently used in series. That will reduce the amount of resealing pressure required.
Word of warning
Remember, check valves are not relief valves. A check valve is intended to make sure fluid goes in only one direction, while a relief valve is a safety device to make sure the system doesn't exceed a certain amount of pressure. Check valves should never be used in applications that involve code related safety issues.
We have a short video for you that goes over the basic question of pressure in check valves. When you want to learn more and get answers to other valve questions, call us at 780-437-0640 or message us below.