TECHNICAL
33
Patrick Gordon continues his series on valves
By Patrick Gordon of Calafrica ( technical @ calafrica . co . za )
Q – What pressure rating should my PCV be if the installation is fed from a supply tank ?
A – Before we can decide on the rating , there are a few things that we need to consider : 1 . What is the purpose of a Pressure Control Valve ? It is used to reduce the incoming main ’ s pressure to a safe system pressure .
2 . Is the tank at such a height that you are receiving pressures above 600 kPa ? A tank 6 meters high will deliver 60kPa static pressure ( roughly 10kPa per 1 meter head of water ). If the pressure is below the maximum designed system pressure , you do not need to fit a PCV as the supply pressure cannot increase unless a pressure pump is added to the design . It is still a requirement to fit an Expansion Relief Valve at the geyser as a safeguard against any unplanned pressure spikes . You need to make sure that there is no flow control device such as a non-return valve between the geyser and the ERV .
3 . Before changing anything on an existing tank fed system , it would be necessary for you to do a proper assessment of the system so that you do not compromise any built-in safety features .
Once again , the most crucial part of any design is the use of a Pressure Gauge and an accurate knowledge of the limitations of all the components that form part of the installation . To summarise , if the pressure from the tank is such that it is below the maximum allowed design pressure you do not need a PCV . PA
All photos by Patrick Gordon
A typical pressure gauge .
“ What is the purpose of a Pressure Control Valve ?”
June 2022 Volume 28 I Number 4 www . plumbingafrica . co . za