The selection of the valve

The valve is one of the medium flow or pressure system facilities, it is used to adjust the flow or pressure of medium. Its functions include cut off or connect medium, flow control, the change of flow, the flow direction of medium change, prevent the reverse flow of medium, control of pressure or discharge pressure. Choose correct valve device to ensure safety in production, improve the service life of the valve, meet the equipment operation is crucial for a long period of time. Choose the valve to know the performance of the medium, flow characteristic, and properties, such as temperature, pressure, flow velocity and flow rate. The following are selected according to the performance of the medium valve.
one, according to the flow characteristic selection valve


the valve opening and closing and the shape of the valve port valve have a certain flow characteristic. When choosing the valve, must consider this.
1。 Truncation and on media use valve: usually choose small flow resistance, flow channel for straight through the valve. This type of valve gate valve, globe valve, plunger valve.
2。 Control flow valves: usually choose easy to flow adjusting valve. Such as regulating valve, throttle valve, plunger valve.
3。 The reversing shunt valve: according to the needs of the reversing shunt, this kind of valve can have three or more channels, suitable for choosing cock valve and ball valve.
4。 Medium with suspended particles with valve: if medium containing suspended particles, suitable for using the open-close part along the sealing surface of slide valve with the wiping. Such as flat gate valve.

2, selected according to connection valve has a variety of valve and pipeline connection, the main thread, flange and welding connection.
1. Threaded connection: the connection is usually end processing of import and export into the valve cone tube or straight thread, make the screwing in taper pipe nipple or pipe. Threaded connection valves mainly under 50 mm nominal diameter of valve.
2. Valve flange connection, flange connection, its installation and disassembly are convenient, but heavy than threaded connection, the corresponding price is also high. So can be applied to a variety of sizes and pressure pipe connection. However, when the temperature exceeds 350 ℃, force a lot of flange connection may occur leakage.
3. Welding connection: the connection is suitable for all kinds of pressure and temperature. But the welding connection valve disassembly and difficult to install, so its use is limited to


run reliably for a long time, or the use of strict and high temperature occasion. Such as coal-fired power stations, nuclear power engineering, ethylene project on the pipeline.
3, according to media performance valve
there are many medium corrosion; The same kind of medium, as the change of temperature, pressure and concentration, its corrosion resistance is different also. Therefore, we should choose according to material corrosion resistance, suitable for the medium of the valve. Depending on the material valve mainly divided into iron valves and plastic valves.
4, according to the selection of temperature and pressure valve
the valve in addition to consider the corrosion medium, flow characteristic, connection form, medium temperature and pressure are important parameters. Use temperature and pressure of valve is determined by manufacturing the material of valve. Use of temperature and pressure valve has certain inner link, and influence each other. Among them, the temperature is the main factor of influence and pressure of the valve only adapted to a certain temperature range, valve temperature change can affect the valve working pressure.
5, according to the flow, the velocity determine valve
the flow valves and flow rate depending on the size of valve, also associated with the structure of medium resistance of the valve, with the pressure of the valve at the same time, temperature and the concentration of the medium, etc. The factors have certain inner link.
1. Port area and the velocity and flow of the valve has a direct relationship, but the flow velocity and flow rate are two interdependent. When traffic must flow velocity, flow area can be smaller; Small flow rate, flow area can be larger. On the other hand, the flow channel area is large, its velocity is small; Port area is small, its velocity.
2. Valve size is the same, its structure is different, the fluid resistance is different also. Under the same conditions, the greater the resistance coefficient of valve, the more fluid flow velocity and flow rate drop across the valve; The smaller the resistance coefficient of valve, the less fluid flow velocity and flow rate drop across the valve.