Steam Globe Valve

What is a steam globe valve?

A steam globe valve is a type of globe valve which is meant for use in controlling the flow of steam. Steam globe valves are used for throttling, opening, and closing fluid flow. These valves are also used to control flow of steam pressure. Steam globe valves are used in different applications such as foods and beverages, pharmaceuticals, and steam power plants among others. When used in applications such as sanitary (for example in foods and pharmaceuticals), these valves are used to release the steam so that it comes into contact with the end product and it has to be very clean. Steam globe valve manufacturers design the body of these valves with a strong metallic material. These helps to give the body high strength to withstand high pressure and high temperatures such as 700 ^oC. Such materials used by steam globe valve manufacturers to make the body include cast iron, ductile cast iron, stainless steel, and carbon steel. Steam globe valves are either manual or automatic valves. The manual steam globe valves are operated by the valve operator using the handwheel while the automatic ones are operated using valve actuators. The valve actuators used in steam globe valves are electric, pneumatic, and hydraulic actuators. 

Figure: Steam globe valve.

Components of a steam globe valve 

Handwheel 

This is the component of a steam globe valve where the valve operator applies force to open, close or regulate fluid flow. The handwheel is used for manual steam globe valves. Automatic valves use actuators to open, close or regulate fluid flow. 

Valve body 

This is the component of a steam globe valve that is used to house internal parts of the valve. Steam globe valve manufacturers design the valve body using different types of metallic materials to enhance valve strength against high pressure, high temperature, and impact damage by falling objects. 

Bonnet 

This is the part of a steam globe valve that is placed on top of the valve body to protect the stem and stem sealing materials. The bonnet has threads that contact the stem threads to rotate the stem when opening, throttling or closing fluid flow. The bonnet is connected to the body via bolts, screws, weld or union connation.

Stem 

The stem is used to connect the valve disc to the handwheel or actuator. The stem is responsible for transmitting torque from the handwheel to the disc to open, close or regulate fluid flow. 

Disc 

This is the component of a steam globe valve that is used to close, open or regulate fluid flow. The disc is connected to the actuator or handwheel through the stem so that it can get operational torque through the stem. 

Seat 

Steam globe valve manufacturers design these valves with two seats. The seats are components where the steam globe valve disc fits to regulate or stop fluid flow. 

Packing 

Packing refers to the sealing material used to cover the stem. Steam globe valve manufacturers use the packing to prevent fluid leakage via the stem. The packing material wears out after a certain period and thus it has to be replaced. 

Cage 

Cage refers to the component of a steam globe valve that surrounds the disc. The cage is located inside the steam globe valve. When the valve disc moves it exposes more openings in the cage which increases the fluid flow rate. Arrangement of cage opening and design highly influences fluid flow rate. The cage in a steam globe valve is used to guide the valve disc into the seat for efficient sealing. 

Figure: Components of a steam globe valve.

How does the steam globe valve work?

A steam globe valve is a uni-directional valve and it is installed in one direction. Steam globe valve manufacturers design these valves for use as either manual or automatic. The most common type is bellow seal globe valve. The working principle of both the manual and the automatic is the same with the difference coming only in terms of the source of torque. For a manual steam globe valve, the valve operator applies force on the handwheel. The force or torque applied on the handwheel is transmuted to the disc to regulate, close, or open fluid flow. The disc in a steam globe valve is responsible for throttling, opening, and closing fluid flow. To open a steam globe valve, the valve operator rotates the handwheel in the counterclockwise direction. This makes the stem rotate as it moves upwards linearly. The stem is connected to the disc. As such, when the stem moves upwards it makes the disc move up. This leaves the steam globe valve open for fluid flow. To close the steam globe valve, the handwheel is rotated in the clockwise direction, this makes the stem and disc move downwards. As such, the disc provides force between the two seats of the steam globe valve and thus closes fluid flow. To regulate fluid flow, the handwheel is rotated in a way that makes the disc partially open and or close as necessary. 

Figure: Working of a steam globe valve.

Types of steam globe valves

Standard pattern steam globe valve 

This type of steam globe valve is also known as the T-pattern steam globe valve. This design is the most common of all steam globe valves. This valve employs a horizontal setting of the seat which allows the disc and stem to move perpendicular to the fluid flow direction. This design of steam globe valve has the highest fluid flow resistance relative to other types of globe valves. The standard pattern steam globe valve has the highest pressure loss and the lowest flow coefficient. These valves are suitable for use in severe flow regulating applications like bypass lines. Also, standard pattern steam globe valves are suitable for use in services where the pressure loss is not a point of concern and where the valve is needed for throttling use only. 

Figure: Standard pattern steam globe valve.

Angle pattern steam globe valve 

This is the steam globe valve in which the inlet and outlet ports are oriented at 90^o degrees. Angle pattern stem globe valve manufacturer design these valves for use where there is pulsating fluid flow because they are capable of handling the slugging effect of the flow. These valves have a low flow coefficient. When the angle pattern steam globe valve is to be installed near a pipe bend, it offers two advantages. One of the advantages is that it greatly reduces fluid flow resistance relative to the standard pattern counterpart. Also, with this angle pattern, the steam globe valve minimizes pipe joints needed and saves piping elbow. 

Figure: Angle pattern steam globe valve.

Oblique pattern steam globe valve 

This is the type of steam globe valve in which the stem and seat are angled at an angle of around 45o degrees. An oblique pattern steam globe valve is a suitable alternative to high-pressure loss which is most common in globe valves. Oblique pattern steam globe valves reduce the fluid flow resistance to a minimum. These valves display straight fluid flow when fully open and this helps to reduce fluid flow resistance.

Figure: Oblique pattern steam globe valve.

Screwed bonnet steam globe valve 

This is a steam globe valve in which the bonnet and the body are connected using screws. This is one of the least expensive and simple designs of a steam globe valve. This type of valve is preferred for use in medium pressure applications. 

Bolted-bonnet steam globe valve 

This is a steam globe valve in which the bonnet and the body are connected using bolts and nuts, this type of connection uses several bolts and nuts which combine their respective torque to create a zero leakage connection suitable for high temperature and high-pressure applications. Most of the steam globe valve manufacturers use bolted connections. 

Pressure seal steam globe valve 

This is a steam globe valve in which the system pressure is used to provide enough force needed against the body’s internal diameter and the surfaces of the bonnet. This design overcomes the disadvantage of weight by tightening the joint using fluid pressure. Bonnet and body seal become tighter when the fluid pressure increases. This type of steam globe valve is best for applications that have high pressure and high temperatures such as steam power plants. 

Welded bonnet steam globe valve 

This is a steam globe valve in which the bonnet and the body are connected using the welding method. Welded bonnet steam globe valves are very economical and reliable when operating at whatever pressure and or temperature. However, these valves cannot be cleaned or repaired unless the weld is removed. For such reasons, welded bonnet steam globe valve manufacturers recommend these valves for use where the valve is expected to be maintenance-free and where cleaning is not required. 

Applications of steam globe valves 

• Used in steam power generation plants. 
• Pharmaceutical industries. 
• Food and beverage industries. 
• Heating, ventilation, and air-conditioning (HVAC) systems.
• Chemical industries. 

Advantages of steam globe valves 

• Good throttling capabilities. 
• They are good in on and off fluid flow. 
• Versatile as they can be used in different fluid flow applications. 
• Strong enough for high-temperature and high-pressure applications. 
• They have zero fluid leakage. 
• Durable as they can be repaired when they break down. 
• Operate faster unlike other valves like gate valve. 

Disadvantages of steam globe valves 

• High-pressure drop. 
• High weight. 
• Employ complex design relative to other valves such as diaphragm valve.
• Produce more noise relative to other valves like gate valves. 

Troubleshooting steam globe valves

Packing leakage

• The packing is loose. Tighten the packing nut. 
• The packing is worn out. Replace the packing. 
• Insufficient packing rings. Add more packing rings. 

Leakage through the seats 

• Worn out seats. Replace the seats. 
• Foreign materials in the valve. Clean the foreign materials. 

Leakage through the body – bonnet connection 

• Loose connection. Tighten the connection bolts or screws. 
• Damaged gasket. Replace the gasket. 
• Damaged metal sealing ring. Replace the metal sealing ring. 

The steam globe valve cannot be opened or closed

• Damaged stem nut. Replace the stem nut.
• Foreign materials in the stem. Remove the foreign materials. 
• The valve packing is over-tightened. Loosen the packing slightly. But remember loose packing will cause fluid leakage. 
• Worn out screw threads. Replace the stem nut. 
• Bend on the stem. Replace or rectify the stem. 

Summary 

A steam globe valve is a type of globe valve used for controlling, opening, and closing steam flow. Steam globe valve manufacturers produce these valves with strong metallic bodies to help them withstand high temperatures and high pressure associated with steam. These valves are operated either manually or they are automatic. Steam globe valves operate by rotating the handwheel which rotates the stem. Rotation of the stem makes it move upwards or downwards to which makes the disc open or close the fluid flow. To regulate fluid flow the valve is opened partially allowing a certain amount of flow rate.

There are various types of steam globe valves which include standard pattern steam globe valve, angle pattern steam globe valve, oblique pattern steam globe valve, welded bonnet steam globe valve, bolted bonnet steam globe valve, screwed-in bonnet steam globe valve, and pressure seal bonnet steam globe valve. These valves are used in different applications such as foods and beverages, pharmaceuticals, chemicals, HVAC, and steam power generation plants among others. Advantages of using these valves are they are versatile, durable, have zero fluid leakage, have a faster operation, easy to install and repair. However, steam globe valves have high weight, high-pressure loss, and a complex design and they produce more noise during operation.