What is a Globe Valve?

A globe valve is a linear motion valve used to stop, start, and regulate the fluid flow. The globe valve disk can be removed entirely from the flow path, or it can completely close the flow path. During opening and closing of globe valve, disc moves perpendicularly to the seat.

The globe valve is used for throttling flow control. Shut off is accomplished by moving the disc against the flow stream rather than across it as in the case with a gate valve. The flow pattern through a globe valve involves changes in direction, resulting in greater resistance to flow, causing a high-pressure drop.

Advantages and disadvantages of Globe valves

ADVANTAGES:

Good shutoff capability
Moderate to good throttling capability
Shorter stroke (compared to a gate valve)
Available in tee, wye, and angle patterns, each offering unique capabilities
Easy to machine or resurface the seats
With disc not attached to the stem, the valve can be used as a stop-check valve

DISADVANTAGES:

Higher pressure drop (compared to a gate valve)
Requires greater force or a larger actuator to seat the valve (with pressure under the seat)
Throttling flow under the seat and shutoff flow over the seat

GLOBE VALVE APPLICATIONS

The following are some of the typical applications of globe valves:

Cooling water systems.
Fuel oil systems.
Feedwater or chemical feed systems.
Boiler and main steam vents and drains.
Turbine lube oil system and others.

Types of Globe Valve

There is three common type of valve.

Z-body type valve

This is the simplest and most commonly used design of globe valves, favorable for applications involving water flow. The name Z-shaped is derived from the Z shaped diaphragm or partition in the bulbous shaped body. The stem and the disc move at right angle to the valve body, aligning with the horizontally arranged seat. The stem passes through the bonnet attached to a wide opening at the top.

Y-body type valve

The Y-body type valve design is a solution to the problem of pressure drop which is commonly found in globe valves. In this design, the valve seat and stem are angled at approximately 45° to the valve axis. This results in a much straighter path for the fluid flow, providing a more pressure resistant environment inside the valve.

The Y-body valves are mainly suited for high-pressure applications wherein problems related to pressure drop are common. However, in the case of throttling purpose, the pressure resistance might not work effectively, especially if the valve is smaller in size. This is also because, in smaller valves, the flow passage is not as carefully streamlined as that in larger vessels.

Angle Valve design

The angle globe valve is a modification of the design of the basic Z-shaped glove valve. The inlet and outlet ends are placed at right angles and the diaphragm is generally a simple flat plate. The fluid flows through the valve body in a right-angled flow path and gets discharged downwards in a more symmetrical manner. These characteristics are extremely important in applications involving high pressure. However, in moderate conditions, the valve functions more or less similar to the Z Shaped Valve.