A check valve is designed to have a process assume one direction only within a piping system. The fundamental design and purpose of a check valve is to hinder backflow in a pipeline system with the aim of appraising piping system safety levels as well as averting fluid overflows; thus, a check valve is often referred to as a one way check valve, or commonly referred to as a one-way valve, or non-return valve. There are many different configurations of check valves which include- inline check valves, swing check valves, ball cone check valves, and y-pattern check valves. Each and every type of these valves has a different application.
One Way Check Valve Operation
A check valve employs a very simple design which allows them to function without human interaction or automation and are therefore solely dependent on fluid flow velocity to either open or close. The least amount o upstream pressure necessary to spur a valve into operation is the cracking pressure. This is a very critical element in the design of one-way valves as it determines the overall design layout and size, the cracking pressure element ranges from one half of a psi to five psi. The degree or lift with which a non-return valve opens up is dependent on the fluid flow rate. A high fluid flow rate translates to a valve with a greater opening, until it reaches the fully open position. For a swing check valve, this maximum opening position usually entails the hinged clapper opening at an angle of about 85 degrees.
Types of Check Valve
There are five common check valves. There’s the swing check valve which has a convex shaped disc as the clapper which faces the upstream inlet area with the opposite side of the clapper being flat. This is a conventional clapper design which requires a restraint to ensure it remains in the pocket. Modern design layouts allow for pin or shaft bosses to ensure the swing valve’s clapper is securely positioned as desired.
The second type is the ball check valve. A ball check valve’s clapper is a spherical ball which is at times spring loaded to ensure sealing at fluid pressures lower than the cracking pressure. This spherical design allows this type of valve to wear out quickly from extensive use caused by regular maintenance. Therefore, they should be installed easily accessible areas to allow for maintenance protocols to be performed on a routine basis.
The third type of check valve is the inline check valve. This type of valve is also called a silent check or a lift check. This type of valve includes a disc that is guided by a center piston in the valve with a spring on the back side. These can often times have very low lift pressures (½ psi).
The fourth type is the y-pattern check valve. This valve is very similar to the swing check but only this valve’s disc sits at an angle to allow for lower pressure lift coming through the valve.
The fifth type is the dual disc. In this valve there is a disc mounted in the center of the pipe but this disc is made of two half moon shapes so when there is process flowing through the valve, the half moons, fold towards each other down stream. There is always a spring between the two half moons of the disc to allow for quick closing of the valve.
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