Forged Steel Gate Valve Types and Working Principle

How does a forged steel gate valve work? 

A forged steel gate valve operates by converting rotary motion from the handwheel to linear motion on the valve disc. When the valve operator rotates the handwheel in the clockwise direction, the valve stem rotates in the same direction. Rotation of the handwheel and the stem several times leads to a continuous linear upward movement of the disc. Moving the disc upwards leaves the valve open, and thus, fluid flows through the valve. When the valve operator rotates the handwheel in the opposite direction, the stem makes the same rotation. As such, the disc moves downwards as the rotary motion is changed to linear motion by the stem threads. Fitting the disc firmly onto the valve seat closes fluid flow rendering the valve closed.

Figure: Working of a forged steel gate valve.

Types of forged steel gate valves 

Forged steel solid wedge gate valve

This is the most commonly used valve because of its simple design and high strength. This valve uses a solid wedge-shaped disc. The wedge is of hollow or solid construction. It has the advantage of being robust and straightforward, but it tends to distort the body due to pipeline and thermal stresses, which may interfere with the valve seat leading to fluid leakage. Like other gate valves, this valve is a bi-direction for all fluids. Forged steel gate valve manufacturers also subject this valve to thermal locking for high-temperature applications.

Figure: Forged steel solid wedge gate valve.

Forged steel conventional parallel gate valve 

This is the version of a forged steel gate valve that uses two discs with springs between them. The use of the springs is to keep the downstream and upstream seats in sliding contact and to enhance the seating load at low pressure. The advantage of this valve is reduced operating effort, economical construction, and reduced maintenance cost. However, these valves have higher pressure relative to the other valves.

Forged steel through-conduit gate valve 

This valve is designed and manufactured according to API 6A and API 6D standards for use in on-off applications. The valve disc has a bore the same size as the valve inlet and outlet. The valve bottom has a hole in the interior. When the valve is started, the disc moves upwards, making its bore concentric to the inlet and outlet ports of the valve. The valve disc moves into the bottom depression when the valve is closed, leading to a tight seal against fluid flow. The valve can withstand high pressure and works well at high temperatures. Forged steel gate valve manufacturers design this valve such that the fluid flows straight through the valve bore from the inlet to the exit port. Such a design leads to low-pressure drop since the fluid flow coefficient of resistance is equal to the one on the piping system. The low-pressure drop property suits the valve for long-distance transportation.

Welded end forged steel gate valve 

The welded end valve is designed with either a butt-weld or socket weld. For the butt weld, the pipe and valve ends are abutted together and then welded to form a high-strength joint. The two butt ends are beveled for connection. This type of connection is used for a valve of any size. The socket weld end valve has the welded end designed with a socket shape. The pipe is inserted into the socket shape, and the two are welded together. Forged steel gate valve manufacturers use the socket end for small valves of less than 2 inches. This type of valve is used where zero fluid leakage is expected. Welded end valves are primarily used where the valve conveys hazardous fluids such as hot water, corrosives, or flammable products. The valve is lighter in weight compared to the valve with flanged ends. However, the valve must be removed entirely from the pipe if it needs repair. As such, the weld has to be removed first. Removing the weld is likely to affect the welded butt and, thus, the quality of the valve to ensure zero leakage is likely to be degraded.

Flanged end forged steel gate valve 

This valve is designed with flanged ends on the inlet and outlet ports. The flanged ends have holes where bolts are inserted. The bolts and nuts are used to connect the valve to the pipe. This type of valve creates a strong joint with a pipe suitable for high pressure and temperature. It also makes it easy to disconnect the valve from the pipe for repairs and cleaning and then reconnect it for continued use. The valve is highly reliable. However, it is heavy compared to the welded end valve due to the two flange ends. Also, this valve’s cost is higher than the other valves.