Pneumatic Butterfly Valve

Pressure Control
In addition to precision flow control, butterfly valves are excellent for pressure control. They experience minimal pressure drop during operation before the fluids recover energy quickly after leaving the valve. This keeps the pump system running efficiently with consistent fluid pressures.

High Durability
Overheating is not a problem of concern with pneumatic actuators, regardless of how excessive the use of the application is. These devices can sustain constant pressures in comparison to alternative devices and therefore offer a longer-term of use.

High Reliability
When it comes to functionality, the pneumatic is viewed to be highly reliable. This is thanks largely to the high control that can be maintained on the conversion of gas to energy. The fact that as mentioned already, they are also highly durable means that performance is of a high standard and these devices have a long life span.

Clean Technology
Pneumatic are the preferred device for use when it comes to applications where hygiene is essential. This is largely down to the use of air as opposed to fluid, with the compressed air being free from harmful chemicals, therefore protecting the application from contamination. This, of course, is critical within the pharmaceutical and food and beverage industries.

Lightweight and Compact
Butterfly valves are great for several applications because they are very lightweight and provide reasonable flow control in a compact design. You will generally want to use a metal-seated valve for more extreme fluid processing, while a soft-seated butterfly valve is best for applications with low pressures and temperatures. The butterfly disc takes up little space but offers enough strength for most pump systems.

Simple and Cost Effective
Butterfly valves are very simple in design and have minimal maintenance requirements. They are easy to install and operate. Plus, they are typically much less expensive than a ball valve of the same size. They do not require much torque to operate effectively and can be automated for energy-efficient operation.

Quick and Efficient
The 90-degree turning radius allows for quick sealing upon actuation, which provides more accurate flow control with minimal effort to turn the valve on and off. Different butterfly valves are to consider, including zero-offset, double-offset, and triple-offset. The pressure will usually determine which type you need. The higher the offset, the more pressure the valve can handle.

Zero Offset Butterfly Valves
In zero offset butterfly valves, also known as concentric butterfly valves, the stem passes through the centerline of the disc that is centered in the seat; all of this is centered inside the valve body. The valve body, seat, and disc lie concentrically when it is in a closed position. The disc rotates on the central axis; this allows a 360° rotation. In a fully-opened position, the flow is divided into two halves on each side of the disc, which is now parallel to the flow. The advantage of this type is that the flowing media does not come in contact with the valve body because the seat is covering it.
Zero offset butterfly valves have resilient soft seats because they depend on the flexibility and deformation of the soft seat during sealing. This causes the disc edges to slide onto the seat, which results in full friction between them during the operation. This reduces the service life of the valve. Since the design requires the seat to be made from a polymeric or elastomeric material, it is limited to lower pressure and temperature ratings.

Double Offset Butterfly Valve (High-Performance Butterfly Valves)
In double offset butterfly valves, the stem axis is offset behind the centerline of the seat and the body (first offset), then the stem axis is further offset from the vertical centerline of the valve (second offset). When the disc is opened, the seat is lifted from the seal; this reduces the friction during the first and last 10 degrees of the valve opening and closing, respectively. This results in a smoother valve operation, better sealing capability, and longer service life than the zero offset butterfly valve.
Like zero offset butterfly valves, double offset butterfly valves use a soft seat. They are available in moderate pressure and temperatures ratings, which are capable of withstanding higher pressures and temperatures than the zero offset butterfly valves in liquid and gas pipelines.

Triple Offset Butterfly Valve
In triple offset butterfly valves, an angular offset in the body sealing cone axis is made in addition to the first two offsets (third offset). This is accomplished by using the right-angled conical profile of the seat coupled with a matching profile at the disc edge. This offset eliminates the contact of the seat and the disc during valve opening and closing, hence, friction is also eliminated. Contact only occurs during the full closure of the butterfly valve; this also acts as a mechanical stop to prevent the disc from rotating further.
The design of triple offset butterfly valves requires the use of metal seats. Since metal seats are tougher and more rigid than soft seats, they can withstand high temperatures and high fluid pressures; this minimizes valve wear. The seats provide sealing that ensures no fluid will escape from the valve. Triple offset butterfly valves have longer service lives than the zero offset and double offset butterfly valves.

Wafer Butterfly Valve
In wafer butterfly valves are placed between two pipe flanges, which are linked by long bolts across the valve body. The valve body may or may not have flange holes outside the valve body. O-rings and gaskets that are mounted in a flat valve face are placed on both sides between the valve body and the pipe flange to achieve a strong seal.
Wafer butterfly valves have the most economical connection design but can not be isolation valves or used in an end-of-line service. The entire pipeline must be shut down when maintenance is performed on either side of the wafer butterfly valve.

Lug Butterfly Valve
Lug butterfly valves are placed between two pipe flanges by the bolts that pass through the threaded inserts (or lugs) protruding outside the valve body. The valve is supported by two separate sets of bolts on each side of the valve and no nuts are used in either lug. This enables the valve to become an isolation valve or to be installed in an end-of-line service. This design enables dismantling on one side of the valve without it affecting the other; this lessens the downtime during maintenance.
However, an additional load is carried by the valve as the weight of the pipeline is also distributed to the valve body. Generally, the pressure rating of butterfly valves is degraded when it is installed in an end-of-line service due to the absence of a downstream flange to help retain the seat in its designed position. The media can deform the seat and push past the disc and seat seal.

Double-Flanged Butterfly Valve
Double-flanged butterfly valves have a pair of flanges built on each side of the valve body; these match the dimensions of the pipe flanges. Two sets of bolts and nuts are used to support the valve on each side; this produces a strong attachment. Double-flanged butterfly valves are more popular in butterfly valves with larger sizing.

Butt-Weld Butterfly Valves
Butt-weld butterfly valves are valves directly welded between pipes; they are used for high-pressure services.

●Valves can be installed in any direction however it is best if it can be installed upright especially in bigger sizes to reduce load on the shaft caused by the actuator or gearbox trying to pull away.
●It is common for smaller butterfly valves to be mounted in various orientations eg water trucks. This is fine and is common practice.
●Verify the material of the butterfly valve, seat and disc before installation. Ensure that there are no defects caused by storage or transportation.
●Verify the pressure rating of the valve vs the application requirement.
●When installing directly to a pump or another valve be sure to have a pipe spacer between them to allow for the butterfly disc to open.
●Complete all welding works before valve installation and be sure the flange has cooled to ambient temperature before installing the butterfly valve.
●Make sure there is no welding residue, waste, rust or other debris in the pipe before installation. Wash with water or a mild detergent if needed.
●Clean the surface of the flange that will come in contact with the butterfly valve to ensure it is free of rust and debris. Wash with water or a mild detergent if needed.
●Make sure there is no warpage of the flange or misalignment of the butterfly valve in relation to the flange. This is the most common cause of butterfly valve problems where it is not aligned with the flange/pipe correctly and the disc catches when trying to open/close. Support the valve where necessary to reduce load from the piping assembly.
●Install spacing bolts taking care not to damage the valve seat and adjust the face to face of the two flanges so there is space when the piping is spread open (enough space to remove the valve or replace it for maintenance).
●Once the pipes are centred, insert the bolts so that the bottom of the valve can rest upon them to prevent the valve from falling through.
Before tightening the bolts operate the valve to ensure it does not catch on the pipework or the flange.
●Tighten the bolts one at a time doing it in stages so even pressure is applied and a seal is formed between the valve and flanges.
●Once the installation is complete operate the valve several times to ensure it is free from impingement and it has not moved during installation.