Important performance when selecting valves

The valve is the control part of the fluid conveying system, which has the functions of cut-off, regulation, diversion, prevention of countercurrent, stabilization, diversion or overflow. The valves used in the fluid control system, from the simplest stop valve to the various valves used in the extremely complex automatic control system, have many varieties and specifications. The valve can be used to control the flow of air, water, steam, various corrosive media, mud, oil, liquid metal and radioactive media. The valve is also divided into cast iron valve, cast steel valve, stainless steel valve, chrome molybdenum steel valve, chrome molybdenum vanadium steel valve, dual phase steel valve, plastic valve, non-standard valve materials.

Valve is used to control the direction, pressure and flow of fluid in the fluid system.

The valve is a device that makes the medium (liquid, gas, powder) in the piping and equipment flow or stop and can control its flow.

Experts of pump valve industry network said that the valve is the control part in the pipeline fluid transportation system, which is used to change the channel section and the flow direction of the medium, with the functions of diversion, cut-off, throttling, check, diversion or overflow pressure relief. The valve used for fluid control, from the simplest stop valve to various valves used in the extremely complex automatic control system, has a wide variety of varieties and specifications. The nominal diameter of the valve ranges from the extremely small instrument valve to the industrial pipeline valve with a diameter of 10 m. The valve can be used to control the flow of water, steam, oil, gas, mud, various corrosive media, liquid metal and radioactive fluid. The working pressure of the valve can be from 0.0013mpa to 1000MPa, and the working temperature can be from - 269 ℃ to 1430 ℃. The valve can be controlled by various transmission modes, such as manual, electric, hydraulic, pneumatic, turbine, electromagnetic, electromagnetic hydraulic, electro-hydraulic, pneumatic, spur gear, bevel gear, etc.; it can be operated according to the predetermined requirements under the effect of pressure, temperature or other sensing signals, or it can be simply opened or closed without depending on the sensing signals. The valve depends on The driving or automatic mechanism makes the hoist move up and down, slide, swing or rotate, so as to change the size of its flow passage area and realize its control function.

The important performance of the valve is as follows: sealing performance

The sealing performance of the valve refers to the ability of each sealing part of the valve to prevent medium leakage, which is the most important technical performance index of the valve. There are three sealing parts of the valve: the contact between the two sealing surfaces of the opening and closing parts and the valve seat; the fitting between the packing and the valve stem and the packing box; and the connection between the valve body and the valve cover. The former leakage is called internal leakage, that is to say, the valve is not tightly closed, which will affect the ability of the valve to cut off the medium. For block valves, internal leakage is not allowed. The last two leaks are called leakage, that is, the medium leaks from the inside to the outside of the valve. Leakage will cause material loss, environmental pollution and even accidents. For flammable, explosive, toxic or radioactive media, leakage is not allowed, so the valve must have reliable sealing performance. Fluid medium

When the medium flows through the valve, there will be pressure loss (the pressure difference before and after the valve), that is, the valve has certain resistance to the flow of the medium. In order to overcome the resistance of the valve, the medium will consume a certain amount of energy. In terms of energy conservation, when designing and manufacturing the valve, the resistance of the valve to the flowing medium should be reduced as much as possible. Opening and closing force and moment

The opening and closing force and moment refer to the force or moment that must be applied when the valve is opened or closed. When closing the valve, it is necessary to form a certain sealing pressure between the two sealing surfaces of the opening and closing parts and the engine seat, and at the same time, it is necessary to overcome the friction between the valve stem and the packing, between the thread of the valve stem and the nut, between the end support of the valve stem and other friction parts, so a certain closing force and moment must be applied. During the opening and closing process of the valve, the required opening and closing force and moment are changed The maximum value is the final instant of closing or the initial instant of opening. The design and manufacture of the valve should strive to reduce its closing force and moment. Opening and closing speed

The opening and closing speed is indicated by the time required for the valve to complete one opening or closing action. Generally, there is no strict requirement for the opening and closing speed of the valve. However, there are special requirements for the opening and closing speed of the rotor pump under some working conditions, such as the requirement for quick opening or closing to prevent accidents, the requirement for slow closing to prevent water hammer, etc., which should be considered when selecting the valve type. Operation sensitivity and reliability

This refers to the sensitivity of the valve to the change of medium parameters. For the throttle valve, pressure reducing valve, regulating valve and other valves used to adjust the medium parameters, as well as the safety valve, drain valve and other valves with specific functions, the functional sensitivity and reliability are very important technical performance indicators. service life

It indicates the durability of the valve, is an important performance index of the valve, and has great economic significance. It is usually expressed by the opening and closing times that can guarantee the sealing requirements, or by the use time.

When selecting valves, we must know the performance of valves in advance. Only when we know the performance of valves, we can choose to use valves better.