Correct selection of valve electric device to prevent overload
Valve electric actuator is used for valve operation and one of the devices connected to valve.
The device is driven by electricity, its movement process can by travel, torque, or to control the size of the axial thrust.
The job characteristics and utilization due to valve electric actuator depends on the type of valve, installation work ethic and the position of the valve in the pipeline or equipment.
So master valve electric device right choice;
Consider to prevent overload (
Work torque is higher than the control torque)
The occurrence of becomes crucial one annulus.
Valve electric device correct selection should be based on: 1.
Operating torque: operating torque is to select the main parameter of valve electric actuator.
Valve electric actuator output torque should be operating maximum moment of 1.
2 to 1.
Operating thrust: there are two kinds of valve electric device of the host structure, one kind is not configured thrust plate, the direct output torque;
Another is to configure the thrust plate, the output torque by thrust plate stem nut can be converted into output thrust.
Output shaft rotation circle count: the number of laps valve electric actuator output shaft rotation with nominal diameter of the valve, the valve stem thread pitch, thread, calculated at M = H/ZS (
Type: M for electric devices should satisfy the total number of rotating ring;
H for the valve opening, mm;
S for the stem drive screw pitch, mm;
Z to stem thread.
Stem diameter: for multi-turn class rising stem valves, if electric device allows the largest stem diameter can't through the stem of the valve, cannot assemble into electric valve.
As a result, the inner diameter of the hollow output shaft electric actuator must be greater than rising stem valves stem diameter.
For part of the rotary valve and multi-turn valves of non-rising stem valves, although need not consider stem diameter through the problem, but also should fully consider when selecting the valve stem diameter and the size of the keyway, after assembly to work properly.
Output speed: the valve opening and closing speed, easy to produce water hammer.
Therefore, we should according to the different conditions of use, select the appropriate opening and closing speed.
Installation and connection mode: the electric device installation has installed vertical, horizontal, fall to the ground;
Connection mode is: have thrust disc stem through (
Rising stem multi-turn valves)
Non-rising stem multi-turn not thrust disc stem part by rotary electric actuator USES is very wide, is the realization of program-controlled valve, automatic control and remote control of the indispensable equipment, its main use on the closed valve.
But can't ignore the special requirements of valve electric device -
Must be able to limit torque and axial force.
Valve electric device adopts usually limiting torque shafts.
When the specifications of the electric actuator was determined, the control torque is also determined.
When its in a predetermined time, motor generally do not overload.
But if appear the following situations can make its overload: 1.
Low voltage power supply and can not get the required torque, the motor stop running.
Setting a torque limit institutions, wrongly, that makes it more than stop torque, excessive torque caused by the continuous, make the motor stop running.
As at intermittent use, the heat generated by the savings, more than the permissible temperature rise of the motor.
A torque limit institutions circuit for some reason fails, the torque is too big.
Using the environment temperature is too high, relative to bring down the heat capacity of the motor.
Above are some of the reasons for overload, for these reasons the motor overheating phenomenon should be given in advance, and take measures to prevent overheating.
Past the motor protection method is to use a fuse, overcurrent relay, thermal relay, thermostat, etc. , but these measures also are each have advantages and disadvantages, for this kind of variable load equipment, electric actuator is not absolutely reliable measures for the protection of.
So must adopt the mode of combination of various methods.
But because the load of every electric device is different, it is difficult to put forward a unified way.
But for the most part, also can find common ground.
Overload protection ways, divided into two kinds: 1.
Increase or decrease of the motor input current judgment;
In the judgement of motor itself fever.
The above two ways, both the heat capacity of the given time allowance to consider motor.
If a single way to that of the heat capacity characteristics of the motor is difficult.
So should choose according to the cause of the overload can reliable method of action -
Combined composite method, in order to realize the comprehensive overload protection.
Overload of basic protection method is: 1.
Continuous operation of motor or point operation overload protection by using a thermostat;
The protection of motor blocked using thermal relay 3.
Use fuse or overcurrent relay for short circuit accident.
Correct selection of the valve electric actuator and is alawys related to prevent overload, should be taken into consideration seriously.
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