check valves, stop check valves, y type lift check valves, dual plate check valves
The check valve design consists of a valve body, bonnet and a disc which is attached to a hinge and swings away from the valve seat to allow fluid to flow in the forward direction. The disc of the check valve swings from fully closed to fully open position depending on the flow pressure of fluid media. Check valves are designed to pass flow in one direction with minimum resistance and to prevent reverse or back flow with minimal leakage. Some of the different types of check valves are as listed below.
1. Swing Check Valves:
Swing check valves funtion on the principal of a disc hinged on a central pin swinging freely from a fully open position to a fully closed position. The trim design for the swing check valves depends on the process application. From soft seat check valves which provide better leak tightness compared to metal to metal seating surfaces. Combination seats consisting of a metal seat ring with resilient insert also offer better leak tight shut off characteristics.
2.Lift Check Valves:
Lift check valves are designed for application in high pressure service. The basic design of a lift check valve consist of the piston disc which is guided by long contact and a close sliding fit with the perfectly centered dash pot. The seat design of a lift-check valve is similar to a globe valve. The Y type lift check valves have a tendency to stay in the open position when service fluid has been trapped above the piston. Large lift check valves are furnished with an equalizer line between the chamber above the disc and the downstream side of the valve to facilitate balance of pressure.
3. Dual Plate Check Valves:
The dual plate check valve is a popular design in recent times, largely resulted out of solving the problems associated with the swing check valves and the lift check valve.The dual plate check valve design consists of two folding discs spring loaded hinged on a central pin. The unique design of this valve is such that it closes with the reducing pressure in the flow direction with retracting spring tension and does not require reverse flow to close the valve. Further it solves one of the bigger problems of check valves in the industry with no water hammer and non slam function.
4. Stop Check Valves:
The stop check valve is again a dual functionality check valve. It can be used as a check valve as well as a globe valve for full shut off. In principal the design of a stop check valve is very similiar to that of a globe valve. When the valve is fully closed it functions as a globe valve and if the stem is backed off a few turns from the fully closed position it functions as a check valve, as the disc is a floating design which can slide on the stem to provide the lift as in the case of a check valve. The Y type stop check valve is a design variation just as in the case of a lift check valve.