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.
Parts
interchangeability with Fisher
Design "E" Control Valves.
Stocked for
immediate delivery. |
CONSTRUCTION
Interchangeability
of parts throughout the Global product line
allows spare parts inventory to be minimized,
while still providing a variety of design
and flow characteristics. Quick change trim
permits the body to be modified to either
designs "D," "S" or
"Z" as required by flow requirements.
Yoke mounted diaphragm actuators can be
either direct or reverse acting.
CAGE GUIDED
Global designs "D,"
S and "T" feature cage guided
valve plugs, cage retained seat rings,
and either metal or composite seats to
attain the required shutoff of the controlled
fluid. Controlled fluids include steam
and a wide variety of non-gritty, non-sticky
liquids and gases. Available in pressure
balanced design "D" or "T"
and pressure unbalanced design "S."
Balanced constructions
have equal pressure above and below the
valve plug. Plug forces are small, enabling
the use of smaller actuators on higher
pressure drops than with pressure unbalanced
construction.
POST GUIDED
Global design "Z
" is an unbalanced, post guided,
construction used to control the flow
of non-lubricating, viscous, or other
hard to handle fluids. Special plug designs
are available for accurate control of
very low flows. |
