Butterfly valves generally above DN300mm in the world have gradually replaced gate valves.Compared with gate valve, butterfly valve has short opening and closing time, small operation moment, small installation space and light weight.Take DN1000 as an example, butterfly valve is about 2T, and gate valve is about 3.5T, and butterfly valve is easy to be combined with various driving devices, with good durability and reliability.
Rubber seal butterfly valve disadvantage is for throttling use, due to improper use will produce cavitation, so that the rubber base spalling, damage, etc.To this end, now the international development of metal seal butterfly valve, cavitation zone reduced, in recent years, China has also developed metal seal butterfly valve, in recent years in Japan also developed corrosion resistance, low vibration, low noise comb butterfly valve.
The life of the general sealing seat under normal conditions, rubber 15 -20 years, metal 80 -90 years.But how to choose correctly depends on the condition requirements.
The relationship between the opening and the flow of the butterfly valve is basically linear proportional change.If used for flow control, its flow characteristics and piping flow resistance is also closely related, such as two pipelines installation valve diameter, form, etc. are all the same, and pipeline loss coefficient is different, the flow of the valve will be very different.
If the valve is in a large throttling state, the back of the valve plate is prone to cavitation, there is the possibility of damage valve, generally used at 15° outside.
Butterfly valve in the opening, the valve body and disc front of mouth shape to valve shaft as the center, on both sides of the form a complete different state, the butterfly plate on one side of the front end of downstream water direction, the other side of the upstream water direction, therefore, on one side of the valve body and valve plate form like opening nozzle shape, on the other side is similar to throttle aperture openings, nozzle side of more quickly than the throttling lateral velocity, and the side of the throttle valve will produce negative pressure, under the rubber seals often can appear fall off.
Butterfly valve operating torque, due to the opening and closing direction of the valve different values, horizontal butterfly valves, especially large diameter valves, due to the water depth, valve shaft, the torque produced by the water head difference can not be ignored.In addition, the valve inlet side device elbow, the formation of deflection, torque will be increased.When the valve is in the middle opening, the operating mechanism needs to be self-locked due to the action of water flow moment.