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Construction of Globe Valve

Nov 09, 2018

Construction of Globe Valve
Though the construction and design of globe valve is usually made according to the requirements,  there are three main designs of the globe valve
Z-body type valve
Y-body type valve
Angle 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 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 get 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.

Globe valves are used for both low and high temperature applications. In low temperature applications the globe valves are so installed that the pressure is under the disk. This helps in easy operation of the valve and also for protecting the packing and preventing erosion to the seat and disk. For high temperature, the valves are so installed that the pressure is above the disk. This would prevent the steam below the disk from contracting upon cooling and tend to lift the disk off the seat.

Arrangement

Both the valve seat and the disc are arranged at right angle to the axis of the valve. The seat can either be screwed into the valve chest or can be a part of the body. The seating can either be flat or mitered and the stem would be threaded above or below the stuffing box. The spindle is held in the valve disc by a nut and the leakage is prevented using stuffing box, which is packed with packing material and gland.