Plumbing Connection Summer 2016

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TION SUMMER 2016 43
on the main valve’s diaphragm to create a degree of opening
that maintains the downstream pressure set point over a
range of flows.
Generally, the main valve will be 40mm in diameter
or larger, and there are a number of makes available in
Australia. The various pilot operated PRVs have generally
the same method of operation and characteristics.
However, some types are able to achieve different levels of
performance at different flow rates, and at zero flow.
One of the main benefits of using Pilot Operated PRVs is
that the hysteresis is minimised, as the main valve does not
depend on a heavy internal spring for operation. As a result,
there is a minimum drop off in downstream set pressure at
rapid change in flow rate, and a small rise in downstream
pressure above the valve set point at low or zero flow in the
pipeline.
Depending on the brand of valve, parallel smaller PRVs
(either Direct Acting or Pilot Operated) may be required to
supply the desired downstream reduced pressure.
There are some models available that are able to regulate
down to zero flow without needing additional parallel PRVs.
Some Pilot Operated PRVs may exhibit ‘hunting’, or create
pressure fluctuations in the pipeline, when operating at
different levels in series in a building. This can be due to each
PRV being influenced by PRVs on the inlet, and also may
be caused by PRVs on the outlet side creating very rapid
changes in pressure throughout.
There are a number of techniques for minimising this
issue. A common approach is to use air release valves to
ensure that any air trapped in the pipeline is eliminated.
This is a very brief outline of these common varieties of
pressure reducing valves. These products form an extremely
important aspect of the correct operation of pipeline
systems in building services.
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Supervision
Data
Log
Controller
2
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For more information on pressure reducing valves or any
other products used in specific applications or overall
pipeline systems contact .
ONE OF THE MAIN BENEFITS OF USING
PILOT OPERATED PRV’S IS THAT THE
HYSTERESIS IS MINIMISED.