Valves - butterfly valves and diaphragm valves

1, butterfly valve brief

The butterfly valve adopts a disc type opening and closing member, and the disc-shaped valve flap is fixed on the valve stem. The valve stem rotates 90 ” to complete the opening and closing action, and the operation is simple. When the valve opening angle is between 20 and 75°, the flow rate is linear with the opening angle. This is the throttling characteristic of the butterfly valve. Therefore, in many cases, the butterfly valve is replaced. The regulating valve of the globe valve and the automatic control system, especially in the case of large flow adjustment.

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 of high temperature media.

2, the advantages and disadvantages of the butterfly valve

(1) Advantages

1) Opening and closing is convenient, labor-saving, and the fluid resistance is small, and it can be operated frequently;

2) Simple structure, small size and light weight;

3) The mud can be transported and the liquid is accumulated at the mouth of the pipe;

4) A good seal can be achieved at low pressure;

5) The adjustment performance is good.

(2) Disadvantages

1) The use pressure and operating temperature range are small;

2) Poor sealing.

3, butterfly valve installation and maintenance should pay attention to the following matters

(1) When installed, the disc should be stopped in the closed position;

(2) The opening position shall be determined according to the rotation angle of the disc;

(3) Butterfly valve with bypass valve, open the bypass valve before opening;

(4) Installation should be carried out according to the manufacturer's installation instructions. A heavy-duty butterfly valve should be provided with a solid foundation.

4, diaphragm valve

Diaphragm valve is a special form of shut-off valve that appeared in the 1920s. Its opening and closing member is a diaphragm made of soft material, which separates the valve body cavity from the bonnet cavity and the driving member, so it is called a diaphragm valve. Diaphragm valves can be divided into six types according to the structure: house type, direct current type, cut-off type, straight-through type, gate type and right angle type; the connection form is usually flange connection; according to the driving method, it can be divided into manual, electric and pneumatic. The pneumatic drive is divided into three types: normally open, normally closed and reciprocating.

5, the characteristics of the diaphragm valve

The characteristics of the diaphragm valve are as follows:

(1) The most prominent feature is that the diaphragm separates the lower valve body cavity from the inner cavity of the upper bonnet, so that the valve stem, valve disc and other parts located above the diaphragm are not corroded by the medium, eliminating the packing sealing structure and not generating The medium is leaking.

(2) A separator made of a soft seal such as rubber or plastic has good sealing properties. Since the diaphragm is a consumable part, it should be replaced periodically depending on the characteristics of the medium.

(3) Due to the diaphragm material limitation, the diaphragm valve is suitable for low pressure and relatively low temperature applications.