What is a Globe Valve
|Materials Used||Parts||Salient Features||Uses|
A Globe valves is a linear motion valve and are primarily designed to stop, start and regulate flow. The disk of a Globe valve can be totally removed from the flowpath or it can completely close the flowpath.
Conventional Globe valves may be used for isolation and throttling services. Although these valves exhibit slightly higher pressure drops than straight=through valves (e.g., gate, plug, ball, etc.), they may be used where the pressure drop through the valve is not a controlling factor.
Because the entire system pressure exerted on the disc is transferred to the valve stem, the practical size limit for these valves is NPS 12 (DN 300). Globe valves larger than NPS 12 (DN 300) are an exception rather than the rule. Larger valves would require that enormous forces be exerted on the stem to open or close the valve under pressure. Globe valves in sizes up to NPS 48 (DN 1200) have been manufactured and used.
Globe valves are extensively employed to control flow. The range of flow control, pressure drop, and duty must be considered in the design of the valve to avert premature failure and to assure satisfactory service. Valves subjected to high-differential pressure-throttling service require specially designed valve trim.
- Gun Metal
- Cast Steel
- Stainless Steel
- Cast Iron
- Alloy Steel
- Plastic etc.
Proper material compatibility needs the knowledge of the type, temperature and concentration of the media being handled. It may be necessary to consult the manufacturer of the globe valve for specific properties of the materials used in the valve. Some features to look for are as follows:
Designs of Globe valves:
Globe valves are available in three main body designs, They are as follows:
- Angle design: The inlet and outlet are perpendicular to each other and the purpose is to transferring flow from vertical to horizontal.
- Y-design: Here, the gate valve derives its linear action from the incline between the inlet’s axis and outlet ports.
- Multi-piece design: In the multi-piece design, the bodies of valves are bolted together and here the inlet and the outlet are not of single piece construction.
Parts of globe valves:
Globe valves are usually two-port valves. Ports are openings in the body for fluid or any form of liquid flowing in or out. The two ports can be straight across from each other on the body, or can be angle oriented. The two halves of the globe valve are separated with the help of an internal baffle. This has an opening forming a seat onto which a movable disc can be screwed in to close the valve. In globe valves, the disc is connected to a stem which is operated by screw action or when it is manually operated, the stem is turned by a hand wheel. In other words, globe valves consist of the following movable parts:
- The disk
- The stem, and
- The handwheel
A diagrammatic representation of a globe valve
- Most globe valves have outside screw rising stem construction. Here the threads are away from the line fluid and hence they are easy to lubricate.
- Available in hand wheel operated designs.
- In all globe valves, there are the back seat ring features that facilitate repacking of the stuffing box on line with the valve in fully open position.
- Seat ring which is screwed into the body are replaceable.
- Body & bonnet with liberal sections.
- The globe valves of higher pressure and larger sizes are provided with thrust bearings and also with gear drive arrangements.
- Body spherical form of globe valves, allows for the stresses, turbulence and resistance to flow to be kept to a minimum.
- Globe valves are used where throttling is required.
- They are also used where both throttling and shut-off required.
- Globe valves can also be used for on-off service.
- They are mostly confined to those applications where the valve is normally closed and drop is not important when the valve is open.
- They are also commonly used in those situations where minimum pressure drop and bidirectional on-off service is required.
- Globe valves are used as sampling valves, which are normally shut except when liquid samples are being taken.