FCS Sentinel 2, Руководство пользователя, Страница: 22 / 77

22
2.8.2 Pilot Valve operation
A typical pilot valve is shown in the diagram opposite.
It is constructed with a plunger which has its stem
connected to a diaphragm. The position of the plunger is
dependent on any forces acting either side of the
diaphragm; the force on the lower side being provided
by water pressure and the force on the upper side being
provided by the compression of a spring. The spring
compression can be adjusted by means of an
adjustment bolt which re-positions the top seat of the
spring.
The water flowing into the pilot valve via the inlet port is
restricted. This is typically done by a needle valve which may be either internal to the
pilot valve or external to it (within the pipe feeding upstream water to the inlet of the
pilot valve).
When the pilot valve opens, some of the water flows across the valve (due to pressure
difference) and leaves via the outlet port. A 3
rd port is available, used for control of the
main valve.
The needle valve is sometimes referred to as a
“ speed control ” . It prevents damage to
the PRV (and water network) by limiting the speed of change to volume of water in the
PRV upper chamber.
2.8.3 Pilot operated pressure reducing valve
A pilot operated pressure reducing valve automatically and accurately reduces
downstream water pressure to a specific, adjustable value.
Water
Filter
Pilot
Valve
Pressure
adjustment
bolt
Inlet
(control)
Spring
adjustment
bolt
Outlet