A globe valve is a linear motion control valve. With globe valves we can start, stop and regulate the flow of fluid. The globe valve disk can be totally removed from the flow path or it can completely close the flow path.
When the valve is actuated to open the disk will perpendicularly move away from the seat. 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.
Globe body Valve designs
1. Z-Body Design
- The simplest design
- Most common for water applications
- A symmetrical form that simplifies manufacture, installation, and repair.
2. Y-Body Design
- This design is a remedy for the high pressure drop inherent in globe valves.
- The seat and stem are angled at approximately 45
- The angle yields a straighter flow path (at full opening) and provides the stem, bonnet, and packing a relatively pressure-resistant envelope-body globe valves are best suited for high pressure and other severe services.
- In small sizes for intermittent flows, the pressure loss may not be as important as the other considerations favoring the y-body design.
3. Angle valve
- Simple modification of basic globe valve
- Both function as valve and piping elbow.
- Fluid is able to flow through a single 90 degree turn
Disadvantages of Globe valves
- 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
- Large valve sizes require considerable power to operate
- Especially noisy in high pressure applications.
- 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.