TECHNICAL 43
How does the dirt get past the strainer of the Pressure Control valve ?
By
Patrick Gordon of Calafrica ( technical @ calafrica . co . za )
The plumbing system must always be protected from dirt entering the system .
This is usually done by fitting an inline strainer , with a mesh size not bigger that 710 µ m , at the beginning of the line . As a secondary / backup to the inline strainer the design of the Pressure Control Valve has to incorporate a strainer that is part of the valve . ( see below )
So , with all this protection how does dirt get past the strainers ?
If there is dirt on the downstream side of the valve , you will always find that it is an unbalanced pressure system . You will also find that the cold water line has not been protected by an inline strainer and that the only protection that the system has is the strainer that is incorporated into the PCV . When a mixer is opened , the hot and cold water come into contact with each other . The stronger pressure of the cold water will overpower that of the hot water and push the hot water back towards the PCV . This will simultaneously carry dirt from the cold water line and deposit it inside the valve . The effect of unbalanced pressure on a system is more obvious currently due to the use of water saving fittings being used ( don ’ t remove these fittings , fix the system ).
So , when a valve malfuctions due to dirt in the valve , it is not because the valve has failed , but rather due to the installation not complying with the proper criteria for this type of installation .
I say type of installation because : If no mixer is present in the installation the effect of an unbalanced installation will not have the same result . The installation will however still not comply with the criteria stipulated by law . So next time you find dirt inside the valve , first fix the cause ( balance the system ) and then proceed to clean the valve . If we don ’ t do this the home owner will not receive the proper customer satisfaction and will keep calling you back to fix “ your ” problem . PA images by Patrick Gordon
October 2022 Volume 28 I Number 8 www . plumbingafrica . co . za