The regulating valve electric device is an indispensable device for realizing valve program control, automatic control and remote control, and its movement process can be controlled by the stroke, torque or axial thrust. Since the working characteristics and utilization rate of the valve electric device depend on the type of valve, the working specification of the device and the position of the valve on the pipeline or equipment, the correct selection of the valve electric device prevents overload phenomenon (operating torque is higher than control) Torque) is crucial.
In general, the basis for the correct selection of valve electric devices is as follows:
Operating torque The operating torque is the most important parameter for selecting the electric device of the valve. The output torque of the electric device should be 1.2 to 1.5 times the maximum torque of the valve.
There are two types of mainframe structures for operating the thrust valve electric device: one is to configure the thrust disc without the thrust disc, and the other is to configure the thrust disc, and the output torque is converted into the output thrust through the stem nut in the thrust disc.
Output shaft rotation number The number of rotations of the output shaft of the valve electric device is related to the nominal diameter of the valve, the pitch of the valve stem and the number of threads. It should be calculated according to M=H/ZS (M is the total rotation circle that the electric device should meet). Number, H is the valve opening height, S is the stem drive thread pitch, and Z is the stem thread number).
Stem diameter versus multi-turn type open-end valve. If the maximum stem diameter allowed by the electric device cannot pass through the valve stem of the valve, it cannot be assembled into an electric valve. Therefore, the inner diameter of the hollow shaft of the electric device must be larger than the outer diameter of the stem of the open rod valve. For the partial rotary valve and the dark rod valve in the multi-turn valve, although the problem of the diameter of the stem is not considered, the diameter of the stem and the size of the keyway should be fully considered in the selection, so that the assembly can work normally.
If the opening and closing speed of the output speed valve is too fast, water hammer is likely to occur. Therefore, the appropriate opening and closing speed should be selected according to different conditions of use.
Valve electric devices have special requirements, and pneumatic control valves must be able to limit torque or axial forces. Usually the valve electric device uses a torque limiting coupling. When the specification of the electric device is determined, the control torque of the self-operated regulating valve is also determined. Generally running in a predetermined time, the motor will not be overloaded. However, if the following conditions occur, the overload may be caused: first, the power supply voltage is low, the required torque is not obtained, and the motor stops rotating; second, the torque limiting mechanism is erroneously set to be greater than the stopped torque. Cause continuous excessive torque generation, so that the motor stops rotating; Third, intermittent use, the generated heat accumulation exceeds the allowable temperature rise of the motor; Fourth, for some reason, the torque limiting mechanism circuit fails, causing the torque to pass Large; five is the use of ambient temperature is too high, relative to the motor thermal capacity decreased.
In the past, the protection of the motor was to use fuses, overcurrent relays, thermal relays, thermostats, etc., but these methods have their own advantages and disadvantages. For the variable load device of the electric device, there is no absolute and reliable protection method. Therefore, various combinations must be adopted, which can be summarized in two ways: one is to judge the increase and decrease of the input current of the motor; the second is to judge the heat of the motor itself. In either case, the time margin given by the thermal capacity of the motor must be considered.
Generally, the basic protection method of overload is: using a thermostat for overload protection of continuous or jog operation of the motor; using a thermal relay for the protection of the motor stall; and using a fuse or an overcurrent relay for a short circuit accident.
The distribution of the valve market is mainly based on the construction of engineering projects. The largest users of valves are petrochemical industry, power sector, metallurgical department, chemical industry and urban construction department. The petrochemical industry mainly uses API standard gate valves, globe valves and check valves; the power sector mainly uses high-temperature pressure gate valves, globe valves, check valves and safety valves for power stations and some low-pressure butterfly valves and gate valves for water supply and drainage valves; Stainless steel gate valve, globe valve, check valve; Shanghai regulating valve metallurgy industry mainly uses low pressure large diameter butterfly valve, oxygen shutoff valve and oxygen ball valve; urban construction department mainly uses low pressure valve, such as urban tap water pipeline mainly adopts large diameter gate valve, building construction Mainly adopting the middle line butterfly valve, the urban heating mainly adopts the metal sealing butterfly valve; the oil pipeline mainly adopts the flat gate valve and the ball valve; the pharmaceutical industry mainly adopts the stainless steel ball valve; the food industry mainly adopts the stainless steel ball valve and the like.
Regarding the market trend of valve products, according to analysis, the main trends in the future are as follows:
1. With the development of oil development to inland oilfields and offshore oil fields, and the development of power industry from thermal power of less than 300,000 kilowatts to thermal power and hydropower and nuclear power of more than 300,000 kilowatts, valve products should also be changed according to changes in equipment application fields. Performance and parameters.
2. Urban construction systems generally use a large number of low-pressure valves, and the development of environmentally friendly and energy-saving type, that is, the transition from low-pressure iron gate valves used in the past to environmentally friendly rubber-plate valves, balance valves, metal-sealed butterfly valves and mid-line sealing butterfly valves. Oil and gas transmission projects are developing in the direction of pipelines, which in turn requires a large number of slab gate valves and ball valves. 3. The other side of energy development is energy conservation, so from the perspective of energy conservation, steam plug valves should be developed and developed to subcritical and supercritical high parameters.
4. The construction of the power station is going to be large-scale, so it is necessary to use large-diameter and high-pressure safety valves and pressure reducing valves, as well as fast opening and closing valves.
5. For the needs of complete sets of projects, the supply of valves has evolved from a single variety to multiple varieties and multiple specifications. The valve required for an engineering project is increasingly being provided by a valve manufacturer.
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