G SERIES GENERAL CATALOG
This design is based on most advance technology available. The G series high performance control valve is an updated version of conventional products. It is designed to work efficiently and effectively under the most demanding circumstances. The characteristic of the trims allow for high universality, simple maintenance and easy operation. Furthermore, the design provides for accurate flow characteristics, wide rangeability, stable operation, and very reliable action. The design is also very easy to test and set for minimum seat leakage.
STRUCTURE & OPERATING PRINCIPAL
857/867-GZ high performance pneumatic diaphragm single seat valve consists of 857/867 pneumatic diaphragm actuators and a GZ single seat valve (Figure 1) or 857/867-GT (Figure 2) high performance pneumatic diaphragm cage valve consisting of 857/867 actuators.
When an air signal enters into the diaphragm chamber, air pressure acts on the operating diaphragm and produces a force with compresses the spring group, thus making the stem travel in the desired direction. This stem travel caused by changing air pressure moves the plug in relation to the seat or cage. This will continue to the air pressure in the actuator and the combined force of the spring and process
pressure have reached equilibrium. This relationship between the air pressure in the actuator and the valve is proportional and is used to control the process fluid. Two types of action are available: Air to Open and Air to Close.
Air to close uses an 857 actuator. When the input signal changes from a low limit to a top limit, the valve position will change from full open to full close.
Air to open uses an 867 actuator. When the input signal changes from a low limit to a top limit, the valve position will change from full closed to full open.
Actuator
The maximum travel for the 857 and 867 actuators is 3.0 inches. The 857 direct action actuator pushes the stem down as the pressure increases. The 867 reverse acting actuator pushes the stem up as the pressure increases. Both the 857 and 867 actuators may have a manual operator installed on the top for emergency use.
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