A quick guide to gate valves
Gate valves are generally used for all sorts of applications and are suitable for installation
both above-ground and underground. It is necessary, not least for underground installations,
to select the correct type of valve to avoid high replacement costs with non-slam check
valve.
Gate valves are designed for an operation that is completely open or fully closed. They are
mounted as insulating valves in pipelines and should not be used as valves for control or
regulation. A gate valve operation is performed by either clockwise closure (CTC) or
clockwise opening (CTO) of the stem rotating motion. The gate moves up- or downward on
the threaded portion of the stem while working the valve stem.
• Reducing the torque requirement of the valve and allowing one-man operation in
order to control the pipeline differential pressure
• A continual flow is permitted with the main valve closed and the by-pass open,
preventing potential stagnation.
• Filling of pipelines postponed.
Swing check valve
When minimal pressure loss and a free bore is required, gate valves are often used. A typical
gate valve has no obstruction in the flow path when completely open, resulting in a very low-
pressure loss, and this design allows a pipe-cleaning pig to be used. A gate valve is a multi-
turn valve, meaning that a threaded stem is used to control the valve. As the valve has to turn
several times to go from open to the closed position, water hammer effects are also prevented
by the slow operation.
It is possible to separate gate valves into two main types: parallel and wedge-shaped. A flat
gate between two parallel seats is used by the parallel gate valves, and the knife gate valve
built with a sharp edge on the bottom of the gate is a common type. Two inclined seats and a
slightly mismatched inclined gate are used in the wedge-shaped gate valves.
Bellows valve
Gate valves with a metal seating wedge were commonly used until the resilient seated gate
valve was introduced to the market. In order to ensure tight closure, the conical wedge shape
and angular sealing devices of a metal-seated wedge need a depression in the valve bottom.
Sand and pebbles are thus embedded in the bore. Regardless of how thoroughly the pipe is
flushed upon installation or repair, the pipe structure will never be fully free from impurities.
Eventually, any metal wedge would therefore lose its capacity to be drop-tight.
Growing stems are attached to the gate, and as the valve is worked, they rise and lower
together, giving a visual indicator of the position of the valve and making it possible to grease
the stem. The threaded stem is rotated around by a nut and moved. This form is only suitable
for above-ground installation.
In the gate, non-growing stems are threaded, and rotate within the valve with the wedge
growing and lowering. Since the stem is held inside the valve body, they take up less vertical
space. To indicate valve location, AVK offers gate valves with a factory-mounted indicator
on the upper end of the stem. Non-rising stem gate valves are ideal for installation both above
ground and underground.
1
/
2
100%