Butterfly valves are broad in all aspects such as media usage, pressure resistance, combinations of materials, operating options and approvals/certifications. For the water sector, the design of butterfly valves is approved for usage in clean potable water, final effluent, air scour duty and UV systems, provided that the appropriate valve materials and liners are used. It is both used for isolation and regulation duties and has excellent flow control functionality.
DESIGNS - Butterfly valves is commonly known as a quarter turn valve. This means that the valve disc moves in a 90 degree movement from fully opened to fully closed and vice versa. The disc will remain inside the waterway at all times. The main advantages of using a butterfly valve are short face to face dimension, both isolating and regulation functions, fast operating times, bi-directional shut off and flexibility in materials and application.
TYPES - AVK manufactures a wide range of butterfly types and designs such as the Wouter Witzel Concentric/Vulcanized liner type. Concentric refers to the relationship between the valve shaft and the sealing face. A concentric butterfly valve design means that the valve shaft is directly aligned with the valve centre lines and the centre of the pipe. Vulcanized Liner, the main characteristics for this type of valve, is a liner bonded or vulcanized to the valve body. It is the interference of the valve disc and the seal/liner in the valve which is what creates the valve seal. The process is highly reliable meaning that the liner cannot move during cyclical operation of the valves. This prevents internal body corrosion and gives excellent sealing properties and low torque. This type of butterfly valve has proven to be leak tight after more than 500,000 movements so it can also perfectly be used in a regulation function.
WIDE CHOICE OF MATERIALS - Due to the special ‘dry shaft’ design only the liner and the disc are in contact with the medium. This makes it possible to use these valves in very abrasive, corrosive and chemical environments. For the water sector, the liner is normally a rubber EPDM or nitrite material, and the disc is stainless steel, or coated ductile iron. However, duplex, aluminium, bronze, hostelry and even titanium are available.
OPERATION - This depends particularly on the application and the function of the valve. Basic manual operation begins on the smaller sizes as a lever operation. Valves above DN250 would require a gearbox option. This can be a hand wheel or cap for tee key operation. All sizes can be supplied and tested with an electric actuator as well as with a pneumatic actuator, whether it’s for on/off applications or full modulating duty. Where applicable this can be supplied with switch boxes, solenoid valves and throttle valves, all wired and tested. The rubber, which is a complex formulation of many ingredients, is developed and tested by AVK’s own R&D scientists, to provide resistance to water treatment chemicals. AVK has the most advanced state of the art mixing facility, which ensures repeatability and high performance materials.
WORKING PRESSURE - Vulcanized butterfly valves can be used up to 25 bar and in vacuum conditions without the liner collapsing.
TEMPERATURE - Due to the vulcanized liner, the valve is suitable for most applications within the water sector, which is generally -20 deg to +110 deg. Other temperature ratings are available on request. For example, when valves are used on air scour duties where air temperatures can exceed these normal rates, AVK can offer a solution using a wide range of valve components and materials.
QUALITY AND LIFE TIME - 100% of the AVK Wouter Witzel valves are being tested before leaving the European factories. All butterfly valves are body tested to 1.5 working pressure, and seat tested to 1.1 working pressure. Test pressures and durations are carried out in line with EN12266-1.