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It's useful to know about the different types of check valves that are out there. Depending upon the industry you work in, you may need a different type of valve based upon the type of fluid as well as what its function is.
The ball check valve is one of the most popular check valves on the market. This specific valve is spring loaded, which helps to keep the valve shut. Reverse flow will keep ball moving toward the seat, which is how the seal is created. These valves are usually small and cheap, which is why they are so commonly used. They are most typically made of metal, however they can be made from other materials depending on the scenario in which they need to be used in.
Other flow check devices are known as a diaphragm check valve. What sets these apart is that there is a flexible rubber diaphragm in place to create a closed valve. As the pressure changes, the diaphragm is able to flex back and forth to allow the flow of a fluid. These can vary significantly based upon the overall diameter of the valve itself as well as the fluid. With fewer moving parts, it can be an advantageous valve to look into.
Stop-check valves are commonly used for backflow prevention because it has an override control that will stop the flow even if there is a pressure change or a direction of flow. It also allows you to deliberately shut the valve with an external mechanism. This way you have full control of the valve system and the flow of fluid regardless of pressure or direction. You may want one of these valves if you want the ability to stop the flow without waiting on a pressure change.
Swing mechanisms are commonly used in plumbing. This is because it uses what's known as a flapper valve where pressure holds it closed. There is a disc or other movable part that blocks the flow. It can also swing on the hinge, which is the case with firefighting. When there is no forward pressure at all, the gate stays shut. Otherwise it will open, which is why it is used with firefighting as well as will drainage systems to avoid the flow of sewage water.
Another type of check valve is the excess flow check valve. These excess flow valves are disc type valves held open by a spring but closed by excess flow from the line downstream. These valves are widely used in loading and unloading operations when a ruptured hose or disconnected line could cause a dangerous chemical or fuel release.