What is a gate valve?

A gate valve is the most common valve for water supply systems. It represents a linear-motion isolation valve and has a function to stop or allow the flow. Gate valves got their name from the closure element sliding into the flow stream to provide shutoff and, therefore, acting like a gate. Gate valves are used to isolate specific areas of the water supply network during maintenance, repair works, new installations, as well as to reroute water flow throughout the pipeline.

Types of gate valves

Based on construction, gate valves for water supply systems can generally be divided into the following types:

By wedge: parallel gate valves and wedge gate valves

By seat: metal seat or resilient seated gate valves

By stem: with rising or non-rising stem.

Gate valve working principle

Gate valves are normally operated by a handwheel, a valve T-key (wrench) or an actuator. The wheel is attached to a valve stem and transfers rotational energy to it. During the gate valve opening, the rotation of the handwheel turns the threads of the gate stem into the gate and vice versa for closing. This energy moves the gate valve wedge downwards or upwards. In underground gate valve installations, an extension spindle is attached, which allows operation without direct access to the valve itself.

Generally, gate valves are installed in the areas of a pipeline where they will longer remain open or closed, as they generally require sometime to switch between these two positions. However, when the valve needs to be operated quite often or even remotely, motorised gate valves are used (i.e. equipped with an electric actuator).

How to tell if a gate valve is open or closed?

In rising stem gate valves, the stem position tells whether a CNM gate valve is open (outside of the valve body) or closed. In non-rising stem gate valves, it is not easy to determine if the gate valve is fully open, closed or somewhere in between at first sight. A marker of the closing direction (cc for clockwise closing, acc for anti-clockwise closing) can be helpful to determine the position of the wedge. A position indicator is a special device, which is mounted on the gate valve stem and helps a user quickly determine a position of the gate valve.

Most of the gate valves close by a clockwise direction, however, in some countries, utilities use anti-clockwise closing gate valves. Hawle produces both versions of gate valves, which allows to meet local standards of such countries as Australia or New Zealand.

Can you throttle a gate valve?

Since gate valves are isolation valves, they must be used either in the “fully open” or “fully closed” position and must not  be deployed to regulate the water flow. Why a gate valve is not suitable for throttling a flow? When throttling a gate valve, turbulent flow rates through the valve body can cause vibration and cavitation, damaging the wedge and the seat, which will eventually lead to leakages and worse sealing capacities.

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