The overview of Gate Valve

What is a gate valve?

A gate valve is the most common valve used in water supply systems. It represents a linear motion isolation valve that has the function of stopping or allowing flow. Gate valves get their name from the closing element that slides into the flow to provide closure and therefore acts as a gate. Gate valves are used to isolate specific areas of the water supply network during maintenance, repair works, new installations and to re-route the flow of water throughout the pipeline.

Gate valve operating principle

Gate valves are usually operated by a hand wheel, a valve T-key (spanner) or an actuator. The wheel is connected to the valve stem and transmits rotational energy to it. During the opening of the gate valve, the rotation of the handwheel screws the threads of the gate stem into the gate, and vice versa to close it. This energy moves the gate valve wedge down or up. In underground gate valve installations, an extension shaft is attached which allows the valve to be operated without direct contact with the valve itself.

Normally, gate valves are installed in areas of the pipeline that will remain open or closed for longer periods of time, as they usually require some time to switch between these two positions. However, when the valve needs to be operated frequently or even remotely, an electric gate valve (i.e. equipped with an electric actuator) can be used.

Gate valve design and parts

The gate valve's simple design and its ability to be used in many low pressure drop services makes it one of the most commonly used valves today. The gate valve is designed as a full-range valve. This means that the valve port is the same size as the inner diameter of the connecting pipe. A full bore gate valve flows through the fluid without impeding the flow and does not cause a pressure drop in the pipe. This also allows the pipe to be cleaned with a clean cleaner.

Resilient seat gate valves with a non-rising spindle comprise

wedge

ductile iron valve body

seating area

stem (spindle)

spindle bearing

bonnet

Types of gate valves

Depending on their construction, water supply system gate valves can generally be divided into the following categories.

1. Parallel or wedge-shaped gate valves

Parallel sliding gate valves have a flat, parallel-faced, gate-like closing element and are installed between two parallel seats. The so-called knife gate valve is a type of parallel gate valve.

Wedge-shaped gate valves are named after the wedge-shaped gate plate. The wedge is ribbed on both sides and is guided by a slot in the body of the gate valve.

2. Metal seated or resilient seated gate valves

Wedge-shaped gate valves can have either metal or resilient seats. In metal seated gate valves, a wedge slides into a groove at the bottom of the gate body, which usually traps the solids contained in the fluid. For this reason, resilient-seated gate valves provide a tighter shut-off and are preferred in water distribution systems.

In resilient seat gate valves, the wedge, mainly made of ductile iron, is encapsulated in a resilient material (elastomer) and therefore provides a tight seal. Seating occurs between the wedge edge and the valve body. This does not require a recess in the bottom of the valve. As a result, resilient seat gate valves can seal small solids carried by the flow of water. All Hawle gate valves are resiliently seated with a high quality elastomeric vulcanised gate for potable water supplies.

3. Rising Stem Gate Valves or non-rising stem gate valves

The difference between Rising Stem Gate Valves and non-rising stem valves is that they can be fixed (rising stem) or threaded (non-rising stem) to the gate. In rising stem gate valves, the rotating stem rises as the valve opens.

Some of the obvious disadvantages of rising stem valves are

they require more space when the spindle is moved upwards due to their bulky design

They are not suitable for underground or buried installations.

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