Butterfly valve is a rotary valve that opens and closes the valve by turning 90° or about 90° with a disk-shaped closing part (can be round or rectangular, etc.).
Composition: body, disc, stem, and handle.
Function: Seal and adjust
Applications: The water supply and drainage systems of municipal engineering, thermal power plants, nuclear power plants, various water supply systems, thermal pipe networks and sewage treatment systems, the inlet valves of large hydroelectric turbines, electric power, chemical, petroleum, metallurgy, shipbuilding, paper making, urban gas, sewage, food industry and atomic energy and national defense projects, have been successively adopted butterfly valves, and there is a trend of high pressure development.
Applicable: gas and a variety of gases, steam, dry powder, mud, fruit pulp and transport and control of the medium water, condensate, sewage, sea water, a variety of liquids, air suspension mixture.
Development: Butterfly valves with pressure grades from 600PSI to 1500PSI. In the 1970s and 1980s, China has also manufactured PN40 butterfly valves, and at present, China has been able to manufacture PN100 and even higher pressure butterfly valves. The largest butterfly valve we know of in the world is 32 feet (9.75 meters).
Classification by use and function:
Truncated butterfly valve
Regulating butterfly valve
Classification by structural form:
Medium type butterfly valve
Single-eccentric center butterfly valve
Double eccentric butterfly valve
Three-eccentric center butterfly valve
Classification by sealing material:
Rubber sealed butterfly valve
Tetrafluoroseal butterfly valve
Metal sealed butterfly valve
The sealing pair has a hard seal of metal to metal, and a soft seal of metal to rubber or plastic. The sealing ring can be placed on the disc or on the valve body. The following are several typical sealed butterfly valve structures:
- Center line-type butterfly valve
The stem axis line is in the same plane as the center plane of the butterfly plate and intersects vertically with the center line of the valve body pipe, and the area of both sides of the butterfly plate is symmetrical to the stem axis. Structure: Generally made into the form of rubber lining. Features: simple structure, center symmetry (type I) two-way sealing effect is the same, and the flow resistance is small switching torque is also small, so it is widely used in medium and small butterfly valves. Disadvantages: But the shaft head is often in a state of friction, faster than other parts of the wear, easy to leak here, so the rubber lined butterfly valve sometimes in the shaft head lined with tetrafluoron film to reduce friction or increase the spring to compensate for friction. Obviously, if the medium line is made of metal to metal, it is somewhat difficult to seal.
- Single-eccentric center butterfly valve
Structure: The valve shaft deviates from the center plane of the butterfly plate and produces an eccentric h, so that the upper and lower ends of the butterfly plate by the valve shaft are no longer the rotating axis, eliminating the friction and friction loss of the upper and lower shaft. Characteristics: The sealing effect is better, but the sealing effect in the two directions is inconsistent, the general forward (from the valve shaft to the sealing surface) is easy to seal, and the reverse is easy to leak because there is no supporting effect of the sealing surface. However, the use of rubber soft seal, using its elasticity, can achieve a good two-way seal. Disadvantages: Because its sealing contact mechanism belongs to the “BALL IN the CONE” (BALL IN CONE), there are always two points in the opening of the butterfly plate can not be out of contact, when used as adjustment, these two points will wear more than other parts, which will have an adverse effect on the seal. If it is used as a metal hard seal and the two positive cones are matched, the sealing surface will interfere when the butterfly plate is rotated, and the switch will be difficult.
- Double eccentric butterfly valve
Structure: In order to improve the situation of single eccentricity, the valve shaft is offset by a distance e, so that the connection between the axis and the sealing point and the sealing surface are obtuse (greater than 90 degrees), so that there is no interference when sealing, and the tighter the closer, resulting in greater sealing surface compression force. Features: When the valve is opened, the sealing surface of the butterfly plate can be quickly disengaged from the seat and the scraping effect is greatly reduced, and it can be made into a metal sealed valve. Disadvantages: Double eccentric butterfly valves can be designed with rubber, tetrafluoroidal, and metal hard seals. For example, type C, type O, type U is a seal ring and other forms. If you want to make a cone-to-cone metal hard seal without interference, sometimes the secondary eccentricity should be made very large, resulting in the need for a large eccentric moment, so that the opening torque is too large, how to reduce the eccentricity, so that the three eccentric butterfly valve is introduced.
- Regulating butterfly valve
The adjustment characteristics of the butterfly valve are approximately equal percentage, which is one of the reasons why the butterfly valve is suitable for adjustment, and the simple structure can be adapted to large mouth diameter. But in small opening, butterfly valve adjustment performance is not good, easy to produce cavitation erosion vibration and noise. Therefore, it is generally not allowed to adjust and throttle at a small opening (< 15° ~ 20°). The flow rate of the butterfly valve is basically unchanged at 80° ~ 90° close to the fully open position. Therefore, it is not suitable to adjust. The adjustment range of the butterfly valve is generally 20° to 70°. Generally, the structure of the butterfly valve body is relatively simple, the valve stem is generally made into the form of a straight shaft, and the butterfly plate is generally flat symmetrical type (type I). In order to reduce the dynamic water torque, the butterfly plate is also made into a disk type, S type, fishtail type. In order to play a regulating role in the small opening, the gear opening valve appears.
