Basics of Gate Valves That You Should Learn First

Gate valves are used in a wide variety of types of applications and are suitable for both above and below ground installations. For underground installations, it is paramount to select the correct type of valve to avoid high replacement costs.

What is a gate valve?

Gate valves are used in a wide range of types of applications and are suitable for both above and

below ground installations. For underground installations, it is most important to select the correct type of valve to avoid high replacement costs.

Gate valves are designed for full opening or full closing service. They are installed in pipelines as isolation valves and should not be used as control or regulating valves. Gate valves are operated by a rotary motion of the stem, clockwise closed (CTC) or clockwise open (CTO). When the stem is operated, the gate moves up or down on the threaded portion of the stem.

The main types of gate valves are slab gate valve and wedge gate valve. They have a similar appearance in structural form, and when fully open, they have no holes through the gate itself, and the gate retracts into the valve body, saving the height space required for slab and telescopic gate valves. Small design differences make different work way and also allow them to have different applications.

Working simulation of slab gate valve

Slab Gate Valve

What is a slab gate valve?

A slab gate valve consists of a single gate unit that rises and falls between two seat rings. Since the gate slides between the seats, the slab gate valve is suitable for media with suspended particles.

Slab gate valve, also known as single flap valves, are designed to provide isolation when the piping system or component is in the closed position. This type of valve is also not suitable for fluid control (throttling). Like double expansion gate valves, slab gate valves can cause wear and damage to the valve seat and internal components when used for extended periods of time in a throttled condition. The main components of a double expansion slab gate valve are the valve body, bonnet, wedge (gate), seat, and stem. The valve body and bonnet are the main pressure-bearing parts. The seat is usually a floating seat with a spring in the backrest to ensure tightness between the gate and the seat.

Parts of slab gate valve

The main parts of slab gate valve are body, bonnet, wedge (gate) halves, seats, and stem. The body and bonnet are the main pressure-containing parts. The disk(s) are positioned by the stem to block the flow or open the fluid path. The wedge assembly in a double expanding gate valve includes two halves, one male and the other female, which are coupled together, usually with springs.

Wedge Gate Valve

What is a wedge gate valve?

A wedge gate valve consists of a conical gate with a metal-to-metal seal. In contrast to slab gate valves, wedge gate valves are not piggybackable because the bottom of the valve body is left open when the valve is opened. The wedge design adds an auxiliary sealing load, allowing metal-sealed wedge valves to seal at both high and low media pressures. However, with metal-sealed wedge gate valves, inlet sealing is often not possible due to the special pressure of the inlet seal caused by the wedge action. Wedge gate valves have a certain angle, usually 3 or 5 degrees, resulting in a buildup of material in the lower groove of the valve, and particles in the medium may damage the seal seat and loosen it to close.

Application of wedge gate valve

Wedge gate valves are generally used where there are no strict requirements on valve size and harsh occasions. For example, in high temperature and high pressure working media, it is required to ensure long-term sealing conditions when closing. Usually, for the environment with reliable sealing performance, high pressure, high pressure cut-off (differential pressure) and low pressure by (small) differential pressure, low noise, high temperature, low temperature, low temperature media with spirit point and evaporation phenomenon, it is recommended to use wedge gate valve, such as power industry, oil refining, petrochemical, marine oil, urban construction of water and wastewater treatment works, chemical industry, etc.