Advantages and Disadvantages of Globe Valves
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Valve refers to a valve whose closure (disc) moves along the center line of the seat. According to the movement of the disc, the change of the seat opening is proportional to the disc travel. Because the stem opening or closing stroke of this kind of valve is relatively short, and has a very reliable cut-off function, and because the change of the seat opening is proportional to the disc travel, it is very suitable for flow regulation. Therefore, globe valve is very flexible for cutting or regulating and throttling.
Advantage of Globe Valve:
- During the opening and closing process, the friction between the disc and the sealing surface of the valve body is smaller than that of the gate valve, so it is wearable.
- The opening height is generally only 1/4 of the seat passage, so it is much smaller than the gate valve.
- There is usually only one sealing surface on the valve body and disc, so the manufacturing process is better and easy to maintain.
- Because its filler is generally a mixture of asbestos and graphite, it has a higher temperature resistance. Generally steam valves are cut-off valves.
- 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, valve can be used as a stop-check valve
- Simple structure, convenient manufacture and easy to maintenance
- Small working stroke, short opening and closing time.
- Good sealing, low friction between the sealing surfaces and long service life.
- The annular space between the disk and seat ring to gradually close as the valve is closed. This characteristic gives the globe valve good throttling ability, which permits its use in regulating flow.Therefore, the globe valve may be used for both stopping and starting fluid flow and for regulating flow.
- When compared to a gate valve, a globe valve generally yields much less seat leakage. This is because the disk-to-seat ring contact is more at right angles, which permits the force of closing to tightly seat the disk.
- Globe valves can be arranged so that the disk closes against or in the same direction of fluid flow. When the disk closes against the direction of flow, the kinetic energy of the fluid impedes closing but aids opening of the valve. When the disk closes in the same direction of flow, the kinetic energy of the fluid aids closing but impedes opening. This characteristic is preferable to other designs when quick-acting stop valves are necessary.
Disadvantages of Globe valve:
- The minimum flow resistance of globe valve is also higher than that of most other types of valves because the flow direction of medium through the valve has changed.
- Because of the long travel, the opening speed is slower than the ball valve.
- Big flow-resistance and large opening and closing power
- Poor regulation performance
- The most evident shortcoming of the simple globe valve is the high head loss from two or more right angle turns of flowing fluid.
- Obstructions and discontinuities in the flow path lead to head loss. In a large high pressure line, the fluid dynamic effects from pulsations, impacts, and pressure drops can damage trim, stem packing, and actuators.
- In addition, large valve sizes require considerable power to operate and are especially noisy in high pressure applications.
- Other drawbacks of globe valves are the large openings necessary for disk assembly, heavier weight than other valves of the same flow rating, and the cantilevered mounting of the disk to the stem.
- 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
- High fluid resistance, greater force required for opening and closing
- Globe valve is not applicable to medium with particle, high viscosity and easy coking