The Structure, Characteristics, and Notices for Use of Butterfly Valve

Figure 1: Manual butterfly valve used to control the drain pipe.

Butterfly valve consists of valve case and valve body. This valve, which is characteristic of rotatable disc or double plate, can be used to cut off water. Its axis of rotation is perpendicular to the direction of water flow. When the plane of the valve body is perpendicular to the water flow direction, the valve is closed.

Structure of Butterfly Valve

Valve body: as a part of water passage through which the water flows, the body supports the weight of valve, bears the operation force and torque, and transmits the water pressure.

Valve door: when closed, it is required to equip enough intensity to cut off the water flow; and when opened, it has great hydraulic characteristic of small hydraulic loss in the central water flow.

Figure 2: The four main components of butterfly valve are valve body, valve rod, valve seat, and butterfly plate.

Shaft and bearing: it supports the weight of valve door.
Locking mechanism: it is demanded that the valve door of butterfly valve be fully opened or closed.

Bypass valve, bypass pipe: when the main valve is actuated, it reduces the torque and eliminate the vibration under dynamic water.

Air valve: when closed, it replenishes air to the back of butterfly to prevent damage to the steel pipe due to vacuum. It discharges air when the front valve is opened to fill water. The valve has a hollow pontoon suspended under the guide piston, and the hollow pontoon is above the water surface in the volute or pipe. In addition, the vent hole is connected with the atmosphere, so as to supplement or exhaust air in the volute and the pipeline. When the pipeline and volute are filled with water, the pontoon floats to the limit position, and the volute and pipeline are isolated from the atmosphere to prevent water overflow.

Expansion joint: it is easy to install and overhaul, and there is space for steel pipe to expand and contract, when temperature changes.

Sealing device: it is aimed to prevent water leakage between valve body and valve door. The rubber shroud is installed on the valve body or valve door. When the door is closed, compressed air rushes into the shroud, and the shroud expands to seal the circumferential gap. Before opening the door, exhaust the air and retract the shroud and then open the door. The compressed air pressure in the shroud shall be greater than the maximum water head (excluding water hammer pressure rise value) (2-4) *10^5pa. When it is not subject to air pressure or water pressure, the gap between the shroud and the valve door is 0.5-1mm.

Characteristics of Butterfly Valve

Figure 3: Central butterfly plate is disc-shaped.

Simple structure and small dimensions. Due to compact structure and short length, small volume, and light weight, it is suitable for large caliber.

Small fluid resistance. When opened, the effective flow area of the valve seat channel is so large that the fluid resistance is small.

Convenient and rapid opening and closing, good adjustment performance. The butterfly plate can be opened and closed by rotating 90 °. The flow rate can be controlled in stage by changing the rotation angle of the butterfly plate.

The opening and closing torque is small. Since the butterfly plates on both sides of the rotating shaft are basically same under the same action of the medium, the direction of the torque is opposite, so the opening and closing is labor-saving.

The low-pressure sealing performance is good, for the sealing surface materials are generally rubber and plastic. Due to the limitation of sealing ring material, the service pressure and operating temperature range of butterfly valve are small. However, the service pressure and operating temperature range of the hard sealing butterfly valve have been greatly improved.

Notices for Use

with simple structure, small size, light weight, and relatively few components. the butterfly valve consists of only a few key parts. It is also very convenient to open, only to turn switch to 90 degrees.

Figure 4: The appearance and shape of butterfly valve door.

The butterfly valve controls the fluid very well and can increase or decrease the flow at any time. The valve has a certain resistance when transporting any fluid, and the resistance of the butterfly valve mainly comes from itself, such as the thickness of the butterfly valve body. If you want to reduce the resistance to the fluid, the only thing you need to do is to reduce its thickness. The butterfly valve has two sealing types: elastic sealing and metal sealing. For elastic sealing valve, the sealing ring can be embedded on the valve body or attached to the periphery of the butterfly plate. The service life of the valve with metal sealing is generally longer than that of the valve with elastic sealing, but it is difficult to achieve complete sealing. Metal sealing can adapt to higher working temperature, while elastic sealing has the defect of being limited by temperature.

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