The selection of electric valve electric device is mainly based on the principle that the selection of petroleum and chemical electric valve should follow

The selection of electric valve electric device is mainly based on the principle that the selection of petroleum and chemical electric valve should follow

Valve electric device is an indispensable equipment to realize valve program control, automatic control and remote control. Its motion process can be controlled by stroke, torque or the size of axial thrust. Because 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 in the pipeline or equipment, therefore, the correct selection of the valve electric device is crucial to prevent the occurrence of overload (working torque is higher than the control torque).
Usually, the correct selection of valve electric device based on the following:
Operating torque The operating torque is the main parameter for selecting the valve electric device. The output torque of the electric device should be 1.2 ~ 1.5 times of the large operating torque of the valve.
There are two main structure of the operation of the thrust valve electric device: one is not configured with thrust disc, direct output torque; The other is the configuration of thrust disc, the output torque through the thrust disc stem nut into the output thrust.
The number of turning turns of the output shaft of the valve electric device is related to the nominal diameter of the valve stem pitch and the number of threads. It is calculated according to M=H/ZS (M is the total number of turning turns that the electric device should meet, H is the opening height of the valve stem, S is the pitch of the valve stem drive thread and Z is the number of valve stem thread).
Stem diameter for multi-turn open-stem valves, if the large stem diameter allowed by the electric device cannot pass through the valve stem, it can not be assembled into an electric valve. Therefore, the inner diameter of the hollow output shaft of the electric device must be greater than the outer diameter of the stem of the open stem valve. For the dark rod valves in partial rotary valves and multi-rotary valves, although it is not necessary to consider the passage of the valve stem diameter, the valve stem diameter and the key way size 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, it is easy to produce water percussion phenomenon. Therefore, the appropriate opening and closing speed should be selected according to different conditions of use.
Valve electric device has its special requirements, that is, must be able to limit torque or axial force. Usually the valve electric device uses a torque limiting shaft. When the specification of the electric device is determined, its control torque is determined. Generally in the pre-determined time of operation, the motor will not overload. But if the following circumstances may lead to overload: first, the power supply is low, can not get the required torque, so that the motor stops rotating; Second, it is wrong to adjust the torque limiting mechanism, so that it is greater than the stopped torque, resulting in continuous excessive torque, so that the motor stops rotating; Third, intermittent use, heat savings, more than the allowable temperature appreciation of the motor; Fourth, the circuit failure of the torque limiting mechanism occurs for some reason, so that the torque is too large; Fifth, the ambient temperature is too high, so that the heat capacity of the motor decreases relatively.
In the past, the way to protect the motor is to use fuses, overcurrent relays, thermal relays, thermostats, etc., but these methods have advantages and disadvantages. For electric devices such as variable load equipment, reliable protection is not available. Therefore, a variety of combinations must be taken, summed up in two kinds: one is to judge the increase or decrease of the motor input current; The second is to judge the heating situation of the motor itself. Either way, the heat capacity of the motor should be considered for a given time allowance.
Usually, the basic protection method of overload is: for the overload protection of continuous running or point operation of the motor, the thermostat is used; For the protection of motor blocking, thermal relay is used; For short circuit accidents, fuse or overcurrent relay is used.
Petroleum, chemical electric valve selection should follow the principle
Petroleum, chemical electric valve selection should follow the principle
In the face of so many electric valve classification and such a complex variety of conditions, to choose the pipeline system installation of the most suitable electric valve products, we should first understand the characteristics of the electric valve; Secondly should master the selection of electric valve steps and basis; Moreover should follow the selection of petroleum, chemical industry with electric valve principle.
The selection of petroleum, chemical industry electric valve principle: the flow channel is straight through electric valve, its flow resistance is small, usually choose as the cut-off and open medium with electric valve; Easy to adjust the flow of electric valves as flow control; Plug valves and ball valves are more suitable for reversing shunt; The sliding of the closing part along the sealing surface with the wiping effect of the electric valve is most suitable for the medium with suspended particles.
A, cut-off and open medium for electric valves
The flow channel is straight through the electric valve, the flow resistance is smaller, usually selected as the cut-off and open medium with the electric valve. Downward closed electric valve (globe valve, plunger valve) because of its tortuous flow path, flow resistance is higher than other electric valves, so less choice. In the case of allowing a higher flow resistance, the closed electric valve can be used.
Two, control the flow of electric valves
Usually choose easy to adjust the electric valve as the flow control. Downward closing electric valves, such as globe valves, are suitable for this purpose because their seat size is proportional to the stroke of the closing element. Rotary electric valves (plug, butterfly, ball valves) and flex-body electric valves (pinch, diaphragm) can also be used for throttling control, but usually only in a limited range of electric valve calibers. Gate valve is a disc-shaped gate to the circular valve seat mouth to do crosscutting motion, it only close to the closed position, can better control the flow, so it is usually not used for flow control.
Three, reversing shunt electric valve
This electric valve may have three or more channels depending on the need for reversing shunt. Plug and ball valves are more suitable for this purpose, so most electric valves used for reversing shunt use one of these electric valves. But in some cases, other types of electric valves, as long as two or more electric valves are properly connected to each other, can also be used for reversing shunt.
Four, electric valve with suspended particles medium
When there are suspended particles in the medium, it is suitable for the electric valve with the sliding wiping function of the closing part along the sealing surface. If the back and forth movement of the closing piece to the seat is vertical, then it may clamp particles, so this electric valve unless the sealing material can allow embedding particles, otherwise only suitable for basic clean media. Ball valve, plug valve, butterfly valve in the process of opening and closing have a wiping effect on the sealing surface, so it is suitable for use in the medium with suspended particles.
At present, whether in petroleum, chemical, or in other industries of the pipeline system, electric valve application, operating frequency and service is ever-changing, to control or eliminate even low leakage, important, key equipment or rely on electric valves. The final control of the pipeline is the electric valve, the electric valve in various industry areas of service and reliable performance is.