In double seated valves the upward and downward forces on the plug due to reduction of fluid pressure are nearly equalized. It is generally used on bigger size valves and high pressure systems. Actuator forces required are less.
The barrier if installed limits electrical energy flowing into hazardous area. If there is no barrier, typically a fuse in the power distribution system will blow.
A pressure switch typically consists of a spring-loaded plunger actuated by process pressure to operate a micros witch. The pressure at which the micro switch operates is dependent upon spring force, which may be varied by an adjusting nut.
The single seated valve is used on smaller sizes where an absolute shut off is required. The use of single seated valve is limited by pressure drop across the valve in the closed or almost closed position.
The sizes of proximity switches are selected based on sensing distance and mounting requirements.
A cold junction compensated instrument will typically indicate temperature of the location where the T/C wires are shorted.
A solenoid is electrically operated valve. It consists of solenoid coil in which magnetic plunger moves. This plunger is connected to the plug and tends to open or close the valve. There are two types of solenoid valves:
1. Normally Open
2. Normally closed
Use: It is used for safety purpose in different electric work
In closed tank, bottom of the tank is connected to the high pressure side of the transmitter. Top of tank is connected to the lower pressure side of the transmitter. In this way vessel pressure can be measured.
The term SPDT refers to single-pole-double-throw relay contact.