Bellows valves

Bellow valve

Bellows valve in the usual materials of all known brands or a good alternative.

A bellows valve (also known as a globe valve) is a linear valve that is used to stop, start and regulate the flow of fluid. The valve seat can be completely removed from the flow path or the flow path can be completely closed. When opening and closing the bellows valve, the disc moves perpendicular to the seat.

This movement creates the ring-shaped space between the disc and the seat ring that gradually closes when the bellows valve is closed. This feature ensures that the bellows valve is well able to inhibit the flow, which is necessary to regulate the flow.

Bellows valves can be arranged in such a way that the valve seat closes against the current or in the direction of the current.

When the valve closes in the direction of the flow, the fluid's kinetic energy helps close but prevents it from opening. This feature is preferred when a fast-acting seal is required.

Bellows valve seat types:

The bellows valve is available in different seat variants.
The most commonly used seat shapes are:

Ball type

The ball type bellows valve design is used in low pressure and low temperature systems. It is able to limit the flow, but basically it is used to stop and start the flow.

Needle type

The Bellow Type design is the better control valve compared to the other types. A wide range of tapered plugs allows good control in different conditions.

Composite type

The composite seat is used to achieve a better seal. A hard, non-metallic insertion ring is used in the design of the composite seat.

Types of bellows valves

Depending on the type of body, there are three types of valves;

• Z type
• Y type
• Hook type

Z type bellows valve

The simplest design and most common type is a Z-valve body. The Z-shaped partition in the spherical housing contains the seat. The horizontal positioning of the seat allows the stem and seat to move perpendicular to the tubular axis, resulting in a very high pressure loss.

The valve seat is easily accessible through a large opening at the top of the valve body. The stem goes through the valve body.

This design simplifies the production, installation and repair of the bellows valve. This type of valve is used when the pressure drop is not a problem and a pressure limitation is required.

Y type bellows valve

The y-type design is a solution to the high pressure loss problem in Z-type valves. In this type, the seat and stem are positioned at an angle of approximately 45° to the pipe axis. Y-type bellows valves are used in high pressure and other critical applications when it comes to pressure loss.

Angled bellows valve

The angled bellows valve rotates the flow direction 90 degrees without using an external bend and piping. The seat opens against the current. This type of bellows valve can also be used in fluctuating flow conditions.

Types of bellows valves based on the connection of the bonnet

• Screwed bonnet: This is the simplest design that exists and is used for inexpensive valves.
• Bolted bonnet: This is the most popular design and is used in a large number of valves in the world. This requires a gasket to seal the connection between the house and the bonnet.
• Welded Bonnet: This is a popular design where disassembly is not necessary. They are lighter in weight than their bolted counterparts.
• Stuffing box bonnet: This type is widely used for high pressure applications at high temperatures. The higher the pressure, the greater the force on the gasket of a pressure sealing valve.

Application of the bellows valve

Bellows valves are used in systems where flow control is required and where leak tightness is also important. The bellows valve can be used in feed water, chemicals, air, lubricating oil and almost all applications where pressure loss is no problem. This valve is also used as an automatic control valve, but in that case the stem of the valve is a smooth rod instead of a thread and is opened and closed by the lifting movement of a drive system.

Advantages of the bellows valve

• Better sealing compared to a gate valve
• Good for frequent use, because there is no wear and tear on the seat and flap.
• Easy to repair, as the seat and plug are accessible from the top of the valve.
• Shorter stroke lengths for quick operation compared to the gate valve
• Usually operated by an automatic actuator.

Disadvantages of the bellows valve

• High pressure loss due to two or more right angles of flow in the valve body.
• In a large high-pressure line, pulsations and bumps can damage the internal trim parts.
• Large valves require considerable opening power and make a considerable noise.
• Bellows valves are heavier than other valves with the same pressure capacity.
• More expensive than a gate valve.

Control valves

manually-operated, pneumatically-operated and electrically-operated valves made of PVC, stainless steel, brass and bronze. The pneumatic and electric versions are also regularly available. In this category we have also included the toggle valves.

In the case of a control valve, a valve is pressed onto the seat with the aid of a spindle. This valve is usually equipped with a gasket for sealing between the valve and the seat.

There are a number of types of control valves:

• Straight gate valve
• Angled control valve
• Angled spindle control valve

The straight and angled valves cause a lot of resistance in the pipe because there is a lot of directional change of the current through the valve. However, it is one of the most commonly used forms of valve, e.g. the faucet or shut-off valve.

The angled spindle valve can have a much better flow with a lower resistance if the valve as a whole can be pulled out of the flow.