The spring is nestled on top of the armature to keep it down. A motion is transmitted from the stem to the valve as the armature moves up and down within the coils. Current passes to the coils via the electrical connection creating a magnetic field which pulls the armature to the centre of the coil. When the armature moves up, the spring is compressed and the valve open. When current flow ceases, the armature moves down and the spring expands. This causes the valve to close.

Electric motors
Electric motors are divided into:
 A.C. (Alternating Current) motors
 D.C. (Direct Current) motors
A.C. motors are mainly used to generate high power output or torque. It is least used due to its difficulty to control. Alternating current motors are mostly utilised in the industry, on pumps to control the …show more content…
Diaphragm style – this type of pneumatic actuator is made up of a stem in a circular steel housing and a rubber diaphragm. It is ideally used for valves such as globe and diaphragm valves, since these require shorter travel. Figure 16 www2.spiraxsarco.com

b. Rack and Pinion – two racks and one pinion is usually used. The pressure within the chamber of the actuator pushes the pistons away. While they move apart from each other, the racks also move along the pistons in a contrary direction of the two racks. The two racks are entoiled or joined to a pinion at the direct opposite teeth of the pinion. The pinion is turned due to the movement of the two racks. This results in the rotation of the main valve of the water pipe. The rack and pinion pneumatic actuator is ideal for actuating plug valves. Figure 17 www.hydraulicstatic.com
c. Piston style – this is used where the thrust is too small or where the diaphragm actuator’s stroke is too short. Compressed air is applied to a solid piston, contained within a short cylinder. Figure18