1 Key points for valve selection

1.1 Clarify the purpose of the valve in the equipment or device

Determine the working conditions of the valve: the nature of the applicable medium, working pressure, working temperature and operation control methods, etc.;

1.2 Correct selection of valve type

The prerequisite for correct selection of valve type is that the designer fully understands the entire production process and operating conditions. When designers select valve types, they should first understand the structural characteristics and performance of each valve;

1.3 Determine the valve termination method

Among threaded connections, flange connections, and welded end connections, the first two are the most commonly used. Threaded valves are mainly valves with a nominal diameter of less than 50mm. If the diameter is too large, it will be very difficult to install and seal the connection. Flange connection valves are easier to install and disassemble, but are larger and more expensive than threaded valves, so they are suitable for pipe connections of various pipe diameters and pressures. Welded connections are suitable for heavier load conditions and are more reliable than flange connections. However, it is difficult to disassemble and reinstall welded valves, so their use is limited to situations where they can usually operate reliably for a long time, or where the working conditions are harsh and the temperature is high;

1.4 Selection of valve material

When selecting materials for the valve housing, internal parts and sealing surfaces, in addition to considering the physical properties (temperature, pressure) and chemical properties (corrosiveness) of the working medium, the cleanliness of the medium (the presence or absence of solid particles) should also be considered should be considered. In addition, you must also refer to the relevant regulations of the country and the user department. Correct and reasonable selection of valve materials can ensure the most economical service life and best performance of the valve. The valve body material selection sequence is: cast iron-carbon steel-stainless steel, and the sealing ring material selection sequence is: rubber-copper-alloy steel-F4;

1.5 Others

In addition, the flow rate and pressure level of the fluid flowing through the valve should be determined and the appropriate valve selected using available information (such as valve product catalogs, valve product samples, etc.).

2 Introduction to commonly used valves

There are many types of valves, including gate valves, globe valves, throttle valves, butterfly valves, plug valves, ball valves, electric valves, diaphragm valves, check valves, safety valves, pressure reducing valves, traps and emergency shut-off valves, among which are commonly used There are gate valves, globe valves, throttle valves, plug valves, butterfly valves, ball valves, check valves, diaphragm valves, etc. ​

2.1 Gate valve

Gate valve refers to a valve whose opening and closing body (valve plate) is driven by the valve stem and moves up and down along the sealing surface of the valve seat to connect or cut off the fluid channel. Compared with stop valves, gate valves have better sealing performance, smaller fluid resistance, less effort to open and close, and have certain adjustment performance. They are one of the most commonly used stop valves. The disadvantage is that it is larger in size and more complex in structure than the stop valve. The sealing surface is easy to wear and difficult to maintain, so it is generally not suitable for throttling. According to the thread position on the valve stem of the gate valve, it is divided into two categories: open stem type and concealed stem type. According to the structural characteristics of the gate, it can be divided into two types: wedge type and parallel type.

2.2 Stop valve

A globe valve is a valve that closes downward. The opening and closing parts (valve discs) are driven by the valve stem to move up and down along the axis of the valve seat (sealing surface). Compared with gate valves, they have good regulating performance, poor sealing performance, simple structure, convenient manufacturing and maintenance, large fluid resistance, and cheap price. It is a commonly used stop valve, generally used in medium and small diameter pipelines.

2.3 Ball valve

The opening and closing part of the ball valve is a ball with a circular through hole. The ball rotates with the valve stem to open and close the valve. The ball valve has a simple structure, quick opening and closing, easy operation, small size, light weight, few parts, small fluid resistance, good sealing and easy maintenance.