44 TECHNICAL
Q – How does a PCV work ?
By Patrick Gordon of Calafrica ( technical @ calafrica . co . za )
In this edition of the series on valves we will take a closer look at how pressure control valves ( PCVs ) work .
A PCV or Pressure Control Valve has two functions . Firstly , to reduce the incoming mains pressure to an acceptable system pressure . Secondly , to get rid of any build up of pressure that may happen after the pressure reducing functions . Typically the municipality will provide pressures between 500kPa and 900kPa . This may be less or more due to the local conditions and demands . set pressure of the valve . All Pressure Control Valves will regulate the pressure to between 70-85 % of the rating of the valve ( see table below ).
When the PCV is installed it is in an open position and will not be reducing any pressure . This is due to the spring holding the main seat open .
Calafrica / Caleffi
As the pressure in the system builds up it causes the pressure under the diaphram to also increase , thus compressing the main spring . The diaphram is connected to the main seat via the spindle , causing the aperture to close and prevent any further buildup of pressure downstream . The stronger the pressure of the spring the higher the
The difference between the set pressure and the Relief Valve pressure is to allow for expansion of the water in the system due to the water heating in the Hot Water Cylinder . If the system is unbalanced , hot and cold water at different pressures , the Relief Valve will discharge any extra buildup of pressure in the system . This is a safety measure to prevent over-pressurisation of any products in the installation .
So the PCV is an essential component that protects any products that are pressure sensitive downstream of the valve . PA
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www . plumbingafrica . co . za @ plumbingonline @ plumbingonline @ PlumbingAfricaOnline February 2023 Volume 28 I Number 12