Globe Valve
A globe valve, abbreviated as GLV, is a type of valve used for regulating fluid flow, both on/off and throttling, it is a control valve. The name globe valve comes from the globular shape of the valve body. This valve is the most common control valve used and can be found in industries such as the oil and gas, chemical, pharmaceutical, shiping, pulp and paper.
Globe Valve Design Classification
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Globe Valve Disk Styles
Ball Disk - This design is used primarily in relatively low pressure and low temperature systems. It is capable of throttling flow, but is primarily used to stop and start flow.
Composition Disk - Uses a hard, nonmetallic insert ring on the disk which creates a tighter closure. These disks are primarily used in steam and hot water applications. They resist erosion and are sufficiently resilient to close on solid particles without damaging the valve.
Needle Disk (Vee Point Disk) - This design the flow rate is controlled better than other disk designs and a fine regulation is achieved. When you need better throttling in different flow velocity.
Parabolic Disk - It is similar to the ball type disk, but its parabolic design provides a higher flow regulation, having a better behavior against wear.
Plug Disk - Because of its configuration, long and tapered, the plug disk provides better throttling than ball or composition designs. This disk is available in a variety of specific configurations.
Globe Valve Parts
Handwheel and Nut - Manual operated actuators use a handwheel to open or close the valve. They offer the user the ability to position the valve as needed.
Yoke - It connects the valve body or bonnet with the actuating mechanism and can provides support for the gland pull down bolts. On many valves, the yoke and bonnet are designed as a one piece construction. For automated actuated valves, the yoke arms are of a heavier construction to provide adequate support to the actuator. The yoke usually has openings to allow access to the stuffing box. A yoke must be sturdy enough to withstand forces, moments, and torque developed by the actuator.
Stem - There are two methods for connecting the disk and the stem, the T-slot and the disk nut. In the T-slot design, the disk slides over the stem, in the disk nut design, the disk is screwed into the stem.
- Rising Stem - The threaded part of the stem is inside the valve body, and the stem packing is along the smooth part that is exposed to the atmosphere outside. In this case the stem threads are in contact with the flow medium. When rotated, the stem and the handwheel rise together to open the valve. This design is commonly used in the smaller sized low to moderate pressure gate, globe, and angle valves.
- Non-rising Stem - The threaded part of the stem is inside the valve and does not rise. The valve disc travels along the stem like a nut when the stem is rotated. Stem threads are exposed to the flow medium and, as such, are subjected to its impact. This design is used where space is limited to allow linear stem movement, and the flow medium does not cause erosion, corrosion, or wear and tear of stem material.
- Sliding Stem - This stem does not rotate or turn. It slides in and out of the valve to close or open the valve. This design is used in hand lever operated quick opening valves. It is also used in control valves that are operated by hydraulic or pneumatic cylinders.
- Rotary Stem - This is a commonly used design in ball, plug, and butterfly valves. A quarter-turn motion of the stem opens or closes the valve.
Stem Packing - Depending on the application, the packing is to prevent leakage of flow medium to the environment and prevent outside air from entering the valve in vacuum applications. The packing is made of a wearable material and must changed during valve maintenance.
Yoke - It connects the valve body or bonnet with the actuating mechanism and can provides support for the gland pull down bolts. On many valves, the yoke and bonnet are designed as a one-piece construction. For automated actuated valves, the yoke arms are of a heavier construction to provide adequate support to the actuator. The yoke usually has openings or windows to allow access to the stuffing box. A yoke must be sturdy enough to withstand forces, moments, and torque developed by the actuator.
Yoke Bushing - An internally threaded nut held in the top of a yoke through which the valve stem passes. In gate and diaphragm valves, the yoke nut is turned and the stem travels up or down depending upon the direction of rotation of the nut. In the case of globe valves, the nut is held fixed and the stem is rotated through it. Valves which require greater effort to open or close are provided with antifreeze yoke sleeve bearings that minimize the friction between the hardened stem and the yoke bushing.
Cage - The cage includes in the most important parts of the globe valve. It surrounds the valve disc and is located within the valve body. When the disc moves, more opening inside the cage is exposed, and the flow rate increases.
Gland Packing - A gasket that provides a seal between the valve’s stem and the bonnet. It is used to prevent liquid leaks in valve stems and stuffing boxes. The gland should be tightened until the valve is leak proof. Tight the packing to tight may affect the valve movement and may cause damage to the stem.
Disk/Plug - The disc is the part which allows, throttles, or stops flow, depending on its position. A disc is seated against the stationary valve seat or seats when the valve is in the closed position. When the valve is closed, the disc performs pressure retaining functions.
Seat - Globe valve seats are either integrated or screwed in to the valve body. Many globe valves have backseats inside the bonnet. Back seats provides a seal between the stem and bonnet and prevents system pressure from building against the valve packing, when the valve is fully open.
Body - The body is the main pressure containing of the valve and can identified as it forms the mass of the valve. It contains all of the valve’s internal parts that will come in contact with the substance being controlled by the valve. The bonnet is connected to the body and provides the containment that is being controlled.
Globe Valve Standards
- API Standards
- ASME Standards
- ASME B16.5 - Pipe Flanges and Flanged Fittings: NPS 1/2 through 24
- ASME B16.10 - Face to Face and End to End Dimensions of Valves
- ASME B16.20 - Metallic Gaskets for Pipe Flanges: Ring-Joint, Spiral-Wound, and Jacketed
- ASME B16.25 - Buttwelding Ends
- ASME B16.34 - Valves Flanged, Threaded and Welding End
- BSI Standards
- BS 1873 - Specification for steel globe and globe stop and check valves (flanged and butt-welding ends) for the petroleum, petrochemical and allied industries
- BS 2080 - Specification for face-to-face, centre-to-face, end-to-end and centre-to-end dimensions of valves
- BS 5152 - Specification for cast iron globe and globe stop and check valves for general purposes
- BS 5154 - Specification for copper alloy globe, globe stop and check, check and gate valves
- BS 5160 - Specification for steel globe valves, globe stop and check valves and lift type check valves
- BS 5352 - Specification for steel wedge gate, globe and check valves 50 mm and smaller for the petroleum, petrochemical and allied industries
- ISO Standards
- ISO 12149 - Bolted bonnet steel globe valves for general-purpose applications
- MSS Standards
- MSS SP-42 - Corrosion-resistant Gate, Globe, Angle and Check Valves with Flanged and Butt-weld Ends
- MSS SP-61 - Hydrostatic Testing of Steel Valves
- MSS SP-80 - Bronze Gate, Globe, Angle and Check Valves
- MSS SP-81 - Stainless Steel, Bonnetless, Flanged, Wafer, Knife Gate Valves
- MSS SP-84 - Steel Valves — Socket Welding & Threaded Ends
- MSS SP-86 - Guidelines for Metric Data in Standards for Valves, Flanges, Fittings and Actuators
Tags: Valve Advantages and Disadvantages Design Classification