i want to know where we must use swing check valve and where we must use lift check valve in petrochemical companies. what are the differences ? are they different from the appearance? how can we distinguish between them visually?
Most swing check valves have a external plug on one or both sides of the body where there is access to the shaft. Lift checks do not have this feature. As to vertical operation of swing checks. There are many swing checks that have a restraint feature built into the body so they can operate in either the horizontal or vertical position. The main thing most people over look about check valves is the need for maintenance. The pivot pin on swing checks can wear and cause the clapper to not seat properly. In some services the internals can accumulate material and become fouled. Most lift checks have a spring that can fail and cause the valve to malfunction. This is specially true if the valve is installed in the vertical position. All checks should be periodically inspected to assure they can function properly.
A swing check valve consists of a flap or disc of the same diameter as the pipe bore, which hangs down in the flow path. With flow in the forwards direction, the pressure of the fluid forces the disc to hinge upwards, allowing flow through the valve. Reverse flow will cause the disc to shut against the seat and stop the fluid going back down the pipe. In the absence of flow, the weight of the flap is responsible for the closure of the valve. Lift check valves are similar in configuration to globe valves, except that the disc or plug is automatically operated. The inlet and outlet ports are separated by a cone shaped plug that rests on a seat typically metal; in some valves, the plug may be held on its seat using a spring. When the flow into the valve is in the forward direction, the pressure of the fluid lifts the cone off its seat, opening the valve. With reverse flow, the cone returns to its seat and is held in place by the reverse flow pressure. There is typically a larger pressure drop across a Swing check valve than across other types.The lift check valve has two major limitations; firstly, it is designed only for installation in horizontal pipelines, and secondly, its size is typically limited to DN80, above which, the valve would become too bulky. For more details you can refer Spirax Sarco, the leaders in Check Valves manufacturing
Horizontal Lift Check Valve
