buttefly valves definition and the detailed introduction : refers to a valve in which a closing member (valve or disc) is a disc that rotates around the valve shaft to open and close, and is mainly used for cutting and throttling on the pipeline. The butterfly valve opening and closing member is a disc-shaped butterfly plate that rotates around its own axis in the valve body to achieve the purpose of opening and closing or adjusting. The butterfly valve is normally less than 90° from full opening to full closing. The butterfly valve and the butterfly rod have no self-locking capability. For the positioning of the butterfly plate, a worm gear reducer is added to the valve stem. The use of a worm gear reducer not only enables the disc to have a self-locking capability, but also stops the disc at any position and improves the valve’s operating performance.
The characteristics of the industrial special butterfly valve can withstand high temperature, the applicable pressure range is also high, the valve has a large nominal diameter, the valve body is made of carbon steel, and the sealing ring of the valve plate uses a metal ring instead of the rubber ring. Large high temperature butterfly valves are manufactured by steel plate welding and are mainly used for flue ducts and gas pipes in high temperature media
Classified by structure
(1) Center sealing butterfly valve
(2) Single eccentric sealing butterfly valve
(3) Double eccentric sealing butterfly valve
(4) Three eccentric or triple offset sealing butterfly valve
Classified by sealing surface material
(1) Soft sealing butterfly valve:
1) The sealing pair is made of a non-metallic soft material to a non-metallic soft material.
2) The sealing pair is made of a metal hard material to a non-metallic soft material.
(2) Metal hard sealing butterfly valve: The sealing pair is composed of a metal hard material and a metal hard material.
Classified by seal
(1) Forced sealing butterfly valve
1) Elastic sealing butterfly valve. The sealing specific pressure is generated by the valve plate pressing the valve seat, the valve seat or the valve plate when the valve is closed.
2) External torque sealing butterfly valve. The seal specific pressure is generated by the torque applied to the valve shaft.
(2) Pressure sealing butterfly valve. The seal specific pressure is generated by the compression of the spring seal element on the valve seat or valve plate.
(3) Automatic sealing butterfly valve. The seal specific pressure is automatically generated by the medium pressure.
Classified by working pressure
(1) Vacuum butterfly valve. A butterfly valve with a working pressure lower than that of the standard atmosphere.
(2) Low pressure butterfly valve. Butterfly valve with nominal pressure PN<1.6MPa.
(3) Medium pressure butterfly valve. The nominal pressure PN is a butterfly valve of 2.5–6.4 MPa.
(4) High pressure butterfly valve. The nominal pressure PN is a butterfly valve of 10. 0–80.0 MPa.
(5) Ultra high pressure butterfly valve. Butterfly valve with nominal pressure PN>100MPa.
Classified by operating temperature
(1) High temperature butterfly valve. t>450 C butterfly valve
(2) Medium temperature butterfly valve. Butterfly valve with 120 C < t < 450 °C.
(3) Normal temperature butterfly valve. A 40C < t <; 120 C butterfly valve.
(4) Low temperature butterfly valve. A butterfly valve of 100 < t < 40 C.
(E) Ultra-low temperature butterfly valve. t < one 100 C butterfly valve.
Classified by connection type
(1) Wafer type butterfly valve:
(2) Flanged butterfly valve.
(3) lug wafer type butterfly valve.
(4) Welded butterfly valve.
Butterfly valve function
It is necessary to clarify whether the butterfly valve is used to turn on or off the medium in the pipeline, or to regulate and control the flow and pressure of the medium in the pipeline. Valves with different functions have different factors to be considered when designing the sealing pair. If the valve is used to connect or cut off the medium in the pipeline, the valve’s cutting capacity, that is, the sealing performance of the valve, is ensured. Under the premise of corrosion resistance, low, medium and normal temperature valves are often in the form of a soft seal. Medium, high temperature and high pressure valves are in the form of a hard seal; if the valve is used to regulate and control the flow of medium in the pipeline When it comes to pressure, the valve’s inherent adjustment characteristics and adjustment ratio are considered
Before designing, we must first fully understand the process conditions of the process system of the valve, including: medium type (gas, liquid, solid phase and two-phase or multi-phase mixing, etc.), medium temperature, medium pressure, medium flow rate (or flow), power source And its parameters, etc.
Strength and stiffness considerations:
In addition to the static design calculation provided by the Valve Design Manual, the butterfly valve must also consider the dynamic load generated by the medium pressure, flow rate, etc., especially the water hammer energy generated when the butterfly valve in the medium and high pressure piping system is closed. Additional loads that take into account environmental influences and additional loads caused by pipes, bearings, etc.
Pressure loss and circulation capacity:
Pressure loss and flow capacity are essentially the same parameters. Pressure loss is a measure of fluid resistance. It is the difference between valve inlet pressure and outlet pressure. At a given flow rate, its size mainly depends on the structural form of the butterfly valve and the shape of the inner part. And surface roughness design, usually expressed by the flow resistance coefficient. The flow capacity is related to the maximum flow through which the valve flows at a given pressure differential, usually expressed as a flow coefficient.
Usually in the design should consider to minimize the pressure loss of the valve and the maximum flow capacity, generally take measures: 1 valve body channel does not reduce the diameter, there should be no protruding part in the channel, the butterfly shape is a smooth transition. 2 Minimize the surface roughness value of the medium overcurrent portion. 3 The entire channel cross section should be kept as constant or a gentle transition structure.
The driving mode of the butterfly valve can be electric, pneumatic, hydraulic, electrohydraulic, and pneumatic, etc. according to the user’s needs. The output torque of the driving device depends on the input torque required by the butterfly valve, and the input torque of the butterfly valve is also in the form of structure. The degree of sealing, the type of media, the pressure of the medium, the frequency of operation, and the way the control is controlled.
The butterfly valve is suitable for use as a switch or regulating device for conveying various media such as water, oil, gas, water-solid two-phase and gas-solid two-phase flow. Therefore, the sensitivity of the butterfly valve sealing pair to the medium is also considered in the design. One of the important factors is that the design is mainly based on material selection and structural form. For example, for a cutting butterfly valve with a high dust content in the medium, a rubber material with good elasticity is used as a sealing ring, or a multi-layer metal hard sealing ring with a self-cleaning structure is used, and the sealing body is sealed while the sealing pair is relatively moving. It can remove dirt such as particles, or use the purging and cleaning functions to reduce the dust pollution to the sealing pair.
The normal failure mode of the butterfly valve is leakage. The leakage includes external leakage and internal leakage. The external leakage is mainly caused by erosion or corrosion. The internal leakage is mainly caused by the damage of the sealing pair. The commonly used life refers to the use time or the number of actions of the seal pair, which mainly depends on the type of medium, medium temperature, medium pressure, opening and closing frequency, opening and closing speed, etc., so that materials satisfying the working conditions are selected and necessary Heat treatment, for example: material scratch resistance, electrochemical corrosion resistance and fatigue strength. In addition, the life of the sealing pair is closely related to the rationality of the structural design and manufacturing precision.