Rising stem or non-rising stem gate valves

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.

Design & parts of a gate valve

A gate valve has a simple design and can be applied in many low pressure-drop services, which makes it one of the most common valves in use today. Gate valves are designed as full-port valves. This means that the valve port is of the same size as the inner diameter of the connecting pipe. Full-bore gate valve passes the fluid flow without any obstructions to a flow and do not cause a pressure drop in a pipeline. This also allows to clean the pipe using a cleaning pig.

A resilient seated gate valve with a non-rising spindle consists of the following parts:

• wedge

• ductile iron valve body

• seating area

• stem (spindle)

• spindle bearing

• bonnet

• packing.

The body is the largest element of the gate valve. Since the spindle remains in the valve body during rotation, it allows an economical bonnet construction. The valve bonnet itself is joined to the body with bolts, which allows cleaning and maintenance. As the gate valve closes, the wedge travels down until it presses the valve seat, which would mean a complete shutoff. During the opening the wedge slides towards the upper part of the valve body.

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.

Rising stem or non-rising stem gate valves

The difference of rising to non-rising stems is that they may be either fixed (rising stem) or threaded (non-rising stem) to the gate. In rising stem gate valves, the rotating stem rises as the valve is opened. Some clear disadvantages of the rising-stem valves are:

1.due to a bulky design they require a greater amount of space when opened as the spindle travels upwards;

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

How does a non-rising stem gate valve work?

In these types of gate valves, the threads on the stem remain inside the valve body. The valve gate travels up and down the stem threads once the valve stem is rotated. Non-rising stem gate valves​ have an advantage in installations where space is limited, for example, in pumping stations. All Hawle gate valves have a non-rising stem and are therefore suitable for buried service.