The valve electric device is an indispensable equipment to realize valve program control, automatic control and remote control. 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 is crucial to prevent overload (the working torque is higher than the control torque).

通常，正確選擇閥門電動裝置的依據如下：

Generally, the correct selection of valve electric device is based on the following:

操作力矩：操作力矩是選擇閥門電動裝置的主要參數，電動裝置輸出力矩應為閥門操作大力矩的1.2～1.5倍。

Operating torque: the operating torque is the main parameter for selecting the electric device of the valve, and the output torque of the electric device shall be 1.2~1.5 times of the large operating torque of the valve.

操作推力：閥門電動裝置的主機結構有兩種：一種是不配置推力盤，直接輸出力矩；另一種是配置推力盤，輸出力矩通過推力盤中的閥桿螺母轉換為輸出推力。

Operating thrust: there are two main engine structures of the valve electric device: one is to output torque directly without a thrust disc; The other is equipped with a thrust disc. The output torque is converted into the output thrust through the stem nut in the thrust disc.

輸出軸轉動圈數：閥門電動裝置輸出軸轉動圈數的多少與閥門的公稱通徑、閥桿螺距、螺紋頭數有關，要按M＝H／ZS計算(M為電動裝置應滿足的總轉動圈數，H為閥門開啟高度，S為閥桿傳動螺紋螺距，Z為閥桿螺紋頭數)。

Number of rotation turns of output shaft: the number of rotation turns of the output shaft of the electric device of the valve is related to the nominal diameter of the valve, the screw pitch of the valve stem, and the number of screw heads, which should be calculated as M ＝ H ／ ZS (M is the total number of rotation turns that the electric device should meet, H is the valve opening height, S is the screw pitch of the valve stem drive thread, and Z is the number of screw heads of the valve stem).

閥桿直徑：對多回轉類明桿閥門，如果電動裝置允許通過的大閥桿直徑不能通過所配閥門的閥桿，便不能組裝成電動閥門。因此，電動裝置空心輸出軸的內徑大于明桿閥門的閥桿外徑。對部分回轉閥門以及多回轉閥門中的暗桿閥門，雖不用考慮閥桿直徑的通過問題，但在選配時亦應充分考慮閥桿直徑與鍵槽的尺寸，使組裝后能正常工作。

Valve stem diameter: for multi turn rising stem valves, if the large valve 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 output shaft of the electric device is larger than the outer diameter of the stem of the rising stem valve. For non rising stem valves in partial turn valves and multi turn valves, although the passage of the valve stem diameter is not considered, the valve stem diameter and the size of the keyway should also be fully considered when selecting, so that they can work normally after assembly.

輸出轉速：閥門的啟閉速度若過快，易產生水擊現象。因此，應根據不同使用條件，選擇恰當的啟閉速度。閥門電動裝置有其特殊要求，即能夠限定轉矩或軸向力。通常閥門電動裝置采用限制轉矩的連軸器。當電動裝置規格確定之后，其控制轉矩也就確定了。一般在預先確定的時間內運行，電機不會超負荷。但如出現下列情況便可能導致超負荷：一是電源電壓低，得不到所需的轉矩，使電機停止轉動；二是錯誤地調定轉矩限制機構，使其大于停止的轉矩，造成連續產生過大轉矩，使電機停止轉動；三是斷續使用，產生的熱量積蓄，超過了電機的允許溫升值；四是因某種原因轉矩限制機構電路發生故障，使轉矩過大；五是使用環境溫度過高，相對使電機熱容量下降。

Output speed: if the opening and closing speed of the valve is too fast, water hammer is likely to occur. Therefore, proper opening and closing speed shall be selected according to different service conditions. The electric device of the valve has its special requirements, that is, it can limit the torque or axial force. Usually, the valve electric device adopts the coupling with limited torque. When the specification of the electric device is determined, its control torque is also determined. Generally, the motor will not overload when it runs within a predetermined time. However, overload may occur in the following cases: first, the power supply voltage is low, and the required torque cannot be obtained, so that the motor stops rotating; Second, the torque limiting mechanism is wrongly adjusted to make it greater than the stop torque, resulting in continuous excessive torque and stopping the motor; Third, intermittent use, the heat accumulation generated exceeds the allowable temperature rise of the motor; Fourthly, the torque limiting mechanism circuit breaks down for some reason, resulting in excessive torque; Fifthly, the operating environment temperature is too high, which relatively reduces the thermal capacity of the motor.