ARI Armaturen PREDU 700 EN - Manual (Page 4)

Page 2-4 Rev. 0040701000 1714
Operating and installation instructions
PREDU
®
4.2 Operating principles
The pressure reducing valve is a direct acting proportional regulator for regulating the
pressure of fluid, gas and vapour media of Fluid Group II pursuant to Pressure Equipment
Directive 97/23/EC. No auxiliary energy is needed.
In a pressureless state the valve is fully open. The media passes through the valve from the
inlet to the outlet. The downstream pressure sensing point should be positioned at least
10 x DN or a minimum of 1 m away from the valve, and is passed on to the actuator over
the control line pipe (refer to Fig. 5).
For operating temperatures above the allowable actuator temperature (refer to points 4.4
and 5.4) a water seal pot must be installed. The whole system, water seal pot, control line
and actuator must be filled with liquid (by steam with water). The downstream pressure is
converted over the actuator diaphragm in a force working in the disc closing direction.
The spring force is attained in the spindle over a pin and coupling and is opposed through
the diaphragm force, therefore works in the disc open direction. When both forces are
equal, the valve is balanced, and the downstream pressure is maintained constant.
When the downstream pressure is altered the disc either „opens“ or „closes“.