What is a gate valve?

A gate valve is the most common valve in a water supply system. It represents a linear motion isolation valve that has the function of stopping or allowing flow. A gate valve gets its name from the closing element that slides into the flow to provide a shut-off function, thus acting as a gate. Gate valves are used to isolate specific areas of the water supply network during maintenance, repair work, new installations, and to reroute the flow of water throughout the pipeline.

Gate valve design and parts

The gate valve design is simple and can be used in many low-pressure drop services, which makes it one of the most commonly used valves today. The gate valve is designed as a full-pass valve. This means that the valve port is the same size as the inside diameter of the connecting pipe. A full bore gate valve flows through the fluid without impeding flow and does not cause a pressure drop in the pipeline. This also allows the pipeline to be cleaned with a cleaning purge.

Resilient seat gate valves with a non-rising spindle consist of the following components.

● Wedge

● Ductile iron valve body

● Resting area

● Valve stem (spindle)

● Spindle bearing

● Engine cover

● Packing.

The valve body is the largest element of the gate valve. Since the spindle remains in the valve body during rotation, an economical bonnet construction is possible. The bonnet itself is bolted to the valve body for easy cleaning and maintenance. As the gate valve closes, the wedge moves down until it presses against the seat, which means it is completely closed. During the opening, the wedge slides toward the top of the valve body.

Types of gate valves

According to the structure, water supply system gate valves can be generally classified as follows.

● By wedge shape: parallel gate valve and wedge gate valve

● By seat: metal seat or resilient seat gate valves

● By stem: with rising or non-rising stem.

Parallel or Wedge Gate Valves

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

Wedge gate valves are named because of the wedge-shaped gate plate. The wedge is ribbed on both sides and guided by a slot in the body of the gate valve. The wedge guide is used for the following purposes.

1. transfer the axial load applied by the medium on the wedge to the valve body

2. to enable low frictional movement of the wedge in the radial direction

3. prevent the wedge from rotating as it moves between open/closed valve positions (used as an anti-twist lock).

The majority of gate valves used in water distribution systems are wedge gate valves.

Metal-seated or resilient-seated gate valves

Wedge gate valves can have either metal or resilient seats. In metal-seated gate valves, the wedge slides into a recess in the bottom of the gate valve body, which typically traps solids in the fluid. For this reason, resilient seat gate valves provide a tighter shutoff and are preferred in water distribution systems.

In resilient seat gate valves, the wedge, made primarily 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 water flow.

Rising stem or non-rising stem gate valves

The difference between rising stem and the non-rising stem is that they can be fixed (rising stem) or threaded (non-rising stem) to the gate. In a rising stem gate valve, the rotating stem rises as the valve opens. Some of the obvious disadvantages of rising stem valves are

1. due to their bulky design, they require more space to open as the spindle moves upward

2. they are not suitable for underground or buried installations.

How does a gate valve work?

A gate valve is typically used to completely shut off fluid flow or to provide full flow in a pipeline when in the fully open position. Therefore, it can be used in either the fully closed or fully open position. gate valves consist of a valve body, seat and flap, spindle, gland and a wheel for operating the valve.

What are the two basic types of gate valves?

Gate valves can be divided into two main types: parallel and wedge. Parallel gate valves use a flat gate between two parallel seats. The popular type is the knife gate valve with a sharp edge designed on the bottom of the gate.

Where is a gate valve installed?

Typically, gate valves are installed in areas of the pipeline where they will remain open or closed for long periods of time, as they usually require some time to switch between these two positions.