34 TECHNICAL
RPZ valves
By
Patrick Gordon of Calafrica
Q : Is an RPZ valve a type of pressure-reducing valve ? A : This question is easy to answer , and the answer is NO . But what is an RPZ valve then , and where should it be installed ?
RPZ is the acronym for ‘ Reduced Pressure Zone ’ backflow preventer , and can be likened to a double non-return valve with extra features .
The valve is divided into three basic areas A , B and C :
A is the inlet port and is separated from the rest of the valve by the check valve ( 4 ) and the diaphragm ( 2 ). As the pressure builds up on top of the diaphragm it moves the spindle down and closes port ( 3 ). As more pressure builds up it will open the check valve ( 4 ) and fill area B . Once area B is sufficiently pressurised , check valve ( 5 ) will be opened and the water will flow into area C .
If the water supply at A fails , the pressure will drop , and the diaphragm ( 2 ) will no longer keep area B closed . This will result in the water in area B being discharged , and because there is no more pressure to keep check valve ( 5 ) open , it will close and prevent any backflow of water from area C .
But , you may ask , why do we need such an elaborate system to prevent backflow ? Will a normal non-return valve not suffice ? A plain single or even double non-return would prevent water from flowing back , however if they fail due to dirt being trapped on the seat , and that often happens , the non-return will fail , and we would not know about it until the damage is already done . With an RPZ valve there is a visual indication of the failure and you will immediately be able to give the problem your attention .
An RPZ valve ensures that no possible contaminated water can enter into the municipal supply , as all backflow will be discharged to the atmosphere via the discharge port ( 3 ).
The gauge ports ( 7 ) make it easy to check the integrity of the unit with the aid of a simple Pressure Gauge .
For more information , contact your supplier for installation and faultfinding training , or watch this space for the fault finding article . PA
“ With an RPZ valve there is a visual indication of the failure and you will immediately be able to give the problem your attention .”
www . plumbingafrica . co . za @ plumbingonline @ plumbingonline @ PlumbingAfricaOnline April 2021 Volume 27 I Number 2