Check valves
Check valves are automatic valves that open with forward flow and close with backward flow. A common other name for check valve is Non Return Valve (NRV).
The pressure of the fluid passing through a system opens the valve, while any reversal of flow will close the valve. Exact operation will vary depending on the type of check valve mechanism. Most common types of check valves are swing, lift (piston and ball), butterfly, stop and tilting-disk.
Types of Check valves
Swing Check valve
A basic swing Check valve consists of a valve body, a bonnet, and a disk that is connected to a hinge. The disk swings away from the valve-seat to allow flow in the forward direction, and returns to valve-seat when upstream flow is stopped, to prevent backflow.
The disc in a swing type check valve is unguided as it fully opens or closes. There are many disk and seat designs available, in order to meet the requirements of different applications. The valve allows full, unobstructed flow and automatically closes as pressure decreases. These valves are fully closed when flow reaches zero, in order to prevent backflow. Turbulence and pressure drop in the valve are very low.
Lift Check or Piston valve
The seat design of a lift-check valve is similar to a globe valve. The disc is usually in the form of a piston or a ball.
Lift check valves are particularly suitable for high-pressure service where velocity of flow is high. In lift check valves, the disc is precisely guided and fits perfectly into the dashpot. Lift check valves are suitable for installation in horizontal or vertical pipe-lines with upward flow.
Flow to lift check valves must always enter below the seat. As the flow enters, the piston or ball is raised within guides from the seat by the pressure of the upward flow. When the flow stops or reverses, the piston or ball is forced onto the seat of the valve by both the backflow and gravity.
The image is used with permission from [Cameron International Corporation] which retains all rights to that image.
Cast steel swing check valve
Colored check valves
LARGE IMAGES OF VALVES
For a valve of the Rising Stem type, the stem will rise above the handwheel if the valve is opened. This happens, because the stem is threaded and mated with the bushing threads of a Yoke...
For a valve of the non Rising Stem type, there is no upward stem movement if the valve is opened. The stem is threaded into the disk. As the handwheel on the stem is rotated, the disk travels up or down...
Globe valves usually have rising stems, and the larger sizes are of the outside screw-and-yoke construction. Components of the Globe valve are similar to those of the gate valve...
A Globe valve is a linear motion valve and are primarily designed to stop, start and regulate flow. The disk of a Globe valve can be totally removed from the flowpath or it can completely close the flowpath...
A Ball valve is a quarter-turn rotational motion valve that uses a ball-shaped disk to stop or start flow. If the valve is opened, the ball rotates to a point where the hole through the ball is in line with...
Ball valves are basically available in three versions.. full port, venturi port and reduced port. The full-port valve has an internal diameter equal to the inner diameter of the pipe...
A Plug Valve is a quarter-turn rotational motion valve that use a tapered or cylindrical plug to stop or start flow. In the open position, the plug-passage is in one line with the inlet and outlet ports of the valve body...
A Butterfly valve is a quarter-turn rotational motion valve, that is used to stop, regulate, and start flow, and are easy and fast to open...
A basic swing Check valve consists of a valve body, a bonnet, and a disk that is connected to a hinge. The disk swings away from the valve-seat to allow flow in the forward direction...
The seat design of a lift-check valve is similar to a Globe valve. The disc is usually in the form of a piston or a ball. This valves are particularly suitable for high-pressure service where velocity of flow is high...