As the electric valve actuators to achieve equipment valve control, automatic control and remote control is indispensable, and its movement can be stroke, torque or to control the size of the axial thrust. Therefore, the correct choice of valve electric device to prevent overload, critical phenomena. Therefore, the correct choice of valve electric device based on the following:
The first is the operating torque : torque operation is to select the main parameters of electric valve actuators, electric actuator output torque valve operation should be the maximum torque of 1.2 to 1.5 times. Operation thrust: electric valve actuators of the host structure has two kinds: one is not configured thrust plate, the direct output torque; the other is the thrust plate configuration, the output torque is converted to the output thrust through the thrust plate of the stem nut. Output: output shaft rotation number of valve electric device shaft rotation number and valve nominal diameter, pitch, valve stem thread number, according to the M = H / ZS computing ( M is the total rotation number, electric equipment should meet the H valve opening height, S pitch, valve stem drive thread Z for the stem thread number ).
The second is the stem diameter: bright bar on multi-turn valves, if the electric device allows the maximum stem diameter can not be dispensed through the valve stem, valve can not be assembled into power. Therefore, the stem diameter of the electric device hollow output shaft diameter must be greater than the next shot of the valve. On the part of the rotary valve and multi-turn valves in the dark bar valve, though not considered by the stem diameter, but should also take full account of the selection of stem diameter and keyway size, so that work can be assembled.
Finally is the output speed: if the valve opening and closing speed too fast, easy to produce water hammer phenomenon. Therefore, according to the different conditions of use, choose the appropriate opening and closing speed. Electric valve actuators have special requirements, must be able to limit the torque or axial force. Coupling usually electric valve actuators with limited torque. When the electric device specifications determined, the control torque is also determined. The general run within a predetermined time, the motor is not overloaded. But if the following conditions may lead to overload : one is the power supply voltage is low, are not required torque, the motor stops rotating; two is incorrectly set the torque limit agencies, to more than stop the torque, caused by continuous excessive torque, the motor stops rotating; three is the intermittent use, heat accumulation produced, more than to allow the motor temperature rise; four is the torque limit for some reason, the circuit failure, so that torque is too large; five is the use of environmental temperature is too high, relative to the motor thermal capacity.
Therefore, from the above, the basic method of overload protection are: overload protection, continuous operation of the motor to move the operation or the thermostat; on the motor stall protection, thermal relay; the short circuit, the fuse or overcurrent relay.
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