What are Check valves?
Check valves or Backflow Prevention Valves or Non-return valve are valves which allow fluid to flow in only one direction. These valves are activated by fluid pressure in the channel. When the passing fluid pressure exerts on the valve, the valve opens. When the fluid flow in opposite direction it closes automatically.
Like other valves, check valves are used with a variety of media: liquids, air, other gases, steam, condensate, and in some cases, liquids with fines or slurries.
Based on the movement and type of valve, this valve is included in the Self-Operated Valve group.
How does a check valve work?
Check valves are flow sensitive, the internal disc in the valve starts opening while slowly the flow accelerates. The disc begins closing when the flow reduces or fluid flows in the opposite direction. The internal sealing of the check valve disc and the seat depends on the back pressure of the fluid compared to the mechanical force used for the on/off valves. Because of this, the allowable seat leakage rates are greater for check valves than for on/off valves.
Types of Check valve:
1. Lift check valve:
This valve is the same as the piston check valve. Disc functions as a straightener or guide. The initial position of contact disc with the seat. If there is a pressure disc to be lifted, the disc returns contact with the seat graphically. Used to handle liquid / sand-free liquid.
2. Swing Check Valve:
The valve moves regularly to open or close. If there is frequent backflow, the impact of the disc and sandy liquid will damage the seat. If the position of the fully open valve has a tendency to continue to open and the flow of fluid flows, if the acceleration of the current changes slowly, the valve is closed again with its own disc gravity
3. Ball Check Valve:
Suitable for all uses, to handle gas, moisture and liquids that can form a sticky deposit. The ball valve uses a free-floating ball or spring loaded ball resting in a seat ring as the closure element. The ball has a slightly larger diameter than that of the through-hole. The ball is free to move around, if there is pressure, the ball will lift to open the valve opening. The ball sits back to the seat if the fluid pressure decreased or fluid flows in opposite direction.