What is a Globe Valve
A globe valve is a linear motion
valve used to stop, start, and regulate fluid flow.The globe valve disk can be totally
removed from the flow path or it can completely close the flow path. Distinguished property or advantage of this flow control valve is throttling of fluids with good characteristics.You might have often see this valve at the discharge side of pumps for flow control. At the pump discharge side,this valve is often used in combination with check valve and gate valve for better operation and isolation.
Principle of globe valve operation
The essential principle of globe
valve operation is the perpendicular movement of the disk away from the seat.
This causes the annular space between the disk and seat ring to gradually close
as the valve is closed.
 |
| Z-body Globe Valve |
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 simple globe valve
- There is generally High head loss in globe valves.
- In globe valves generally considerable power is required to operate.
- Globe valve is used noisy in high pressure applications.
- In globe valve large openings is necessary for disk assembly.
- Globe valves have heavier weight than other valves of the same flow rating.
- In globe valves there is cantilevered mounting of the disk to the stem.
Globe Valve Body Designs
1. Z-body Globe Valve
This design of globe valve body provides a symmetrical form
that simplifies manufacture, installation, and repair.
2. Y-body Globe Valve
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. Y-body globe valves are best suited
for high pressure and other severe services.
3. Angle Valve
A particular advantage of the angle body
design of globe valve is that it can function as both a valve and a piping elbow. For moderate
conditions of pressure, temperature, and flow, the angle valve loosely resembles the ordinary globe. The angle valve's
discharge conditions are favorable with respect to fluid dynamics and erosion.
Globe Valve Seats
Globe valve seats are either integral with
or screwed into the valve body. Many globe valves have backseats. A backseat is a seating
arrangement that provides a seal between the stem and bonnet. When the valve is fully open, the
disk seats against the backseat. The backseat design prevents system pressure from building
against the valve packing.
Globe Valve Direction of Flow
For low temperature applications, globe and
angle valves are ordinarily installed so that pressure is under the disk. This promotes easy
operation of valve , helps protect the packing, and eliminates a certain amount of erosive action to the
seat and disk faces. For high temperature steam service, globe valves are installed so that pressure
is above the disk. Otherwise, the stem will contract upon cooling and tend to lift the disk off the seat.
