4、 Selection method of pneumatic ball valve The working principle of pneumatic ball valve is to rotate the ball to make the pneumatic ball valve unblocked or blocked. The pneumatic ball valve is light to open and close, small in size, can be made into a large caliber, reliable in sealing, simple in structure, convenient in maintenance, and the sealing surface and spherical surface are often closed, not easy to be eroded by media, so it is widely used in various industries. Pneumatic ball valves can be roughly divided into 19 categories, including floating pneumatic ball valve, fixed pneumatic ball valve, metal hard seal pneumatic ball valve, V-type pneumatic ball valve, wafer type pneumatic ball valve, insulation pneumatic ball valve, pipeline pneumatic ball valve, rail pneumatic ball valve, top mounted pneumatic ball valve, pigging valve, high pressure forged pneumatic ball valve, three-way (four-way) pneumatic ball valve, internal thread pneumatic ball valve Integral pneumatic ball valve, cryogenic pneumatic ball valve, bellows pneumatic ball valve, eccentric semi pneumatic ball valve, all welded pneumatic ball valve, special pneumatic ball valve, etc. The O-type pneumatic ball valve is of floating structure. The ball core is precision casting, and the surface is plated with hard chrome. The valve seat is made of metal or reinforced polytetrafluoroethylene material. The flow port is the same as the pipe diameter, with great flow capacity, minimal flow resistance, and no leakage when closing. It is generally used as an on-off valve, especially suitable for high viscosity, fiber containing, and granular media. The V-type pneumatic ball valve adopts a fixed structure, and the ball core is provided with a V-shaped notch, which can realize proportional adjustment, and the flow characteristic is approximately equal.

3、 Typical failure maintenance plan of pneumatic control valve: take the failure of "control valve acts normally but does not play a regulating role" as an example to explain the maintenance plan: the valve used in the vinyl chloride workshop of a chemical plant is a single seat control valve of a well-known domestic enterprise. This production line has an annual output of 100000 tons of plastic particles. There are two production lines in the compression, conversion and fractionation section of the vinyl chloride workshop. In addition to compression, pneumatic control valves are widely used in conversion and fractionation sections. The working environment of each control valve is completely different, and there is usually only one control valve on each pipeline. Some control valves are also equipped with bypass valves, which can be controlled by manual valves. If the control valve fails, the bypass valve can be opened to ensure normal production. Therefore, before disassembly and inspection, it is necessary to carefully analyze the failure causes of the regulating valve and develop a complete maintenance plan.