SAVE MONEY ADVERTISE YOUR BRAND LISTING
36
TECHNICAL
What happened to the pressure ?
Contributed by Patrick Gordon of Calafrica ( technical @ calafrica . co . za )
Patrick Gordon takes a look at pressure control valves .
Nominal rated system pressure
Pressure control closing pressure ( below system pressure )
Expansion relief discharge pressure ( system pressure )
100kPa ( Blue ) |
70 – 85kPa |
95 – 100kPa |
200kPa ( Black ) |
140 – 170kPa |
190 – 200kPa |
300kPa ( Brown ) |
210 – 255kPa |
285 – 300kPa |
400kPa ( Red ) |
280 – 340kPa |
380 – 400kPa |
600kPa ( Green ) |
420 – 510kPa |
570 – 600kPa |
Q : Why does my Pressure Control Valve not deliver the pressure that it is rated at ?
A : Before we answer that question let us consider the functions of the valve . The valve has two main functions :
1 . The valve will reduce the mains pressure to the desired system pressure . Normally the lowest maximum acceptable pressure of the components used in a system .
2 . The valve will also relieve any excess build-up of pressure for whatever reason . Typically , this would be due to the heating of the Hot Water Cylinder .
When you first measure the set pressure of the valve , you will see that the pressure will always be lower than what it is rated at . A 100kPa valve will only deliver pressure to the value of 70-85kPa . This allows for a certain amount of build-up of pressure before the valve comes to the second function , the relieving of excess pressure when it reaches 95 – 100kPa . If this were not the case , the valve would constantly be opening for expansion . These mentioned values can be used as a percentage for the other pressure ratings of the valves ., for instance , a 400kPa valve will have a set pressure of 280 – 340kPa and a relief pressure of 380 – 400kPa .
All the control valves in the system are related in the differences of their pressures so that there is a uniformity in the level of safety that they provide . Do not tamper with the settings of a valve by placing coins etc . on the spring as this will destroy the engineered safety that is built into every unit . When presented with a problem in an installation , contact the manufacturer before you make any modifications .
Remember it is not knowledge that is power , but how we apply that knowledge that makes us strong . PA
WEB / BRANDLISTINGS
ASSOCIATIONS
SAVE MONEY ADVERTISE YOUR BRAND LISTING
ASSOCIATION
ASSOCIATION
CONTACT : + 27 11 579 4940 sales @ interactmedia . co . za
www . plumbingafrica . co . za @ plumbingonline @ plumbingonline @ PlumbingAfricaOnline February 2024 Volume 29 I Number 12