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.
This movement creates the annular space between the disk and seat ring that gradually close as the valve closed. This characteristic provides the globe valve good throttling ability required for regulating the flow.
Leakage from globe valve seat is less as compared to the gate valve, mainly due to right angle contact between the disk and seat ring, which allows tighter seal between seats the disk.
Globe Valve Disk Types
Globe valve is available in many different types of disc arrangement. Most used disk designs are listed below.
Ball diskdesign is used in low-pressure and low-temperature systems. It is capable of throttling flow, but in principle, it is used to stop and start the flow.
Needle diskdesign provides better throttling as compared to ball or composition disk design. A wide verity of long and tapered plug disks are available to suit different flow conditions.
Composition diskis used to achieve better shutoff. A hard, non-metallic insert ring is used in composition disk design.
Types of Globe Valve
Depending on the type of body there are three types of globe valves;
Z types Globe Valve
The simplest design and most common type is a Z-body. The Z-shaped partition inside the globular body contains the seat. The horizontal seating arrangement of the seat allows the stem and disk to travel at a perpendicular to the pipe axis resulting in a very high-pressure loss.
The valve seat is easily accessible through the bonnet which is attached to a large opening at the top of the valve body. Stem pass through the bonnet like gate valve.
Y types Globe Valve
The y-type design is a solution for the high-pressure drop problem in Z-type valves. In this type, seat and stem are angled at approximately 45° to the pipe axis. Y-body valves are used in high pressure and other critical services where pressure drop is concerned.
Angle types Globe Valve
Angle globe valve turns the flow direction by 90 degrees without using an elbow and one extra pipe weld. Disk open against the flow. This type of globe valve can be used in the fluctuating flow condition also, as they are capable of handling the slugging effect.
Globe Valve Types based on Body Bonnet Connection
Screwed bonnet:This is the simplest design available and it is used for inexpensive valves.
Bolted-bonnet:This is the most popular design and used in a large number of globe valves. This requires a gasket to seal the joint between the body and bonnet.
Welded-Bonnet:This is a popular design where disassembly is not required. They are lighter in weight than their bolted-bonnet counterparts.
Pressure-Seal Bonnet:This type is used extensively for high-pressure high-temperature applications. The higher the body cavity pressure, the greater the force on the gasket in a pressure -seal valve.
Application of Globe valve
Globe Valves are used in the systems where flow control is required and leak tightness is also important.
-It used in high-point vents and low-point drains when leak tightness and safety are major concerns. Otherwise, you can use gate valve for drain and vent.
-It can be used in Feed-water, chemical, air, lube oil and almost all services where pressure drop is not an issue
-This valve is also used as an automatic control valve, but in that case, the stem of the valve is a smooth stem rather than threaded and are opened and closed by lifting action of an actuator assembly.
Globe Valve Advantage
-Better shut off as compared to gate valve
-Good for frequent operation as no fear of wear of seat and disk
-Easy to repair, as seat and disk can be accessed from the valve top
-Fast operation compares to gate valve due to shorter stroke length
-Usually operated by automatic actuator
Globe Valve Disadvantage
-High head loss from two or more right angle turns of flowing fluid within the valve body.
-Obstructions and discontinuities in the flow path lead to a high head loss.
-In a large high-pressure line, pulsations and impacts can damage internal trim parts.
-Large valve require considerable power to open and create noise while in operation.
-It is heavier than other valves of the same pressure rating.
-Costlier compared to gate valve.