Water & Wastewater Asia May/June 2019

INSIGHT | 35
By Roger Lah, Cla-Val Technical Products Specialist
A
recent visitor to Cla-Val’s facility
described the lengthy process that
entails when a power failure occurs
and what that means to his utility’s water
treatment plant operator: The operator
has to quickly close fifteen motorised
valves manually in order to prevent water
overflowing onto the plant floor. The valves
are usually controlled by a Programmable
Logic Controller (PLC) to control flow into
a filtration backwash process, utilising
venturi flowmeters. These types of valves
are susceptible to cavitation problems, and
therefore a hydraulic Pressure Reducing
Valve is normally installed upstream to
reduce the pressure and prevent cavitation.
This traditional arrangement requires
significant piping space for two valves and
a venturi flowmeter. Furthermore, power
failure to the motor operated valve can cause
significant problems.
Fortunately, the hydraulic Pressure Reducing
Valve can now be replaced with a hybrid
multi-function electronic and hydraulic
Metering Valve. This valve is capable of
measuring and controlling flow based on
valve position and differential pressure
sensors installed on the valve. It also
incorporates anti-cavitation trim to prevent
cavitation due to the high pressure drop into
the filtration process.
The electronic Metering function utilises dual
solenoids and simply changing the upstream
by closing the solenoid from Normally Closed
Metering Valve with Anti-cavitation trim and “Power Failure Close” Solenoid
Water & Wastewater Asia • May / June 2019