TECHNICAL
55
As a valve gets older and has worked for a few years the
seat and other parts wear down and then it will also start
to continually drip. Valves do have a lifespan, but the way
valves operate can be an indicator to the health of the
geyser’s electrics such as the thermostat, which may need
to be replaced, in which case the water would continually
boil and there will be hot water released through the relief of
the valve constantly.
MECHANICAL AND ELECTRONIC VALVES
Mechanical valves typically don’t need anything more than
to be installed and then walk away. The spring operation
of a mechanical valve will be calibrated according to the
pressure required by an electronc gauge, and the product
will [hopefully] last its lifespan.
Electronically operated valves are typically solenoid valves.
A solenoid is the generic term for a coil of wire used as an
electromagnet. It also refers to any device that converts
electrical energy to mechanical energy using a solenoid. The
device creates a magnetic field from electric current and
uses the magnetic field to create the desired linear motion.
“The function of the
temperature probe
on a safety valve is
to cause the valve
to open when the
temperature of the
water exceeds the
preset temperate.”
Electronic valves do fit into new buildings that have building
management systems and can also be controlled via an app.
These valves also work with sensor technology. For example
a sensor would be in a drip tray and if the sensor had to get
wet, a signal is sent to the valve to shut off the water supply,
which then puts the valve into the lock position.
As with electronic devices, it can become expensive, which
is why these types of valves are not found in the domestic
market too often.
SAFETY AND STRENGTH
In my opinion, to control water, springs are better. They can
hold up to 2 000kPa according to the standards, which is
twice what we need based on the South African norm. They
are also hydrostatic tested and need to pass 3 000kPa
for 15 minutes. Hydrostatic testing is a type of pressure
test that works by completely filling the component with
water, removing any air contained within the unit, and then
pressurising the system to a set pressure.
Temperature/Pressure (TP) valves are designed so that
if a geyser is over-pressurised for whatever reason, they
are able to release at 1.5 times their nominal rating, so a
400kPa valve would release at 600kPa and a 600kPa valve
will release at 900kPa to reduce any excess pressure that
www.plumbingafrica.co.za
The challenge with electronics is that you needs power/
electricity to operate them. Typically electronic solenoid
valves are used in specific application such as process
control installations and are not generally used on domestic
installations or commercial installations.
A design example of a cutaway showing a TP or
temperature and pressure valve.
has come into the system (by mistake) that is also very
dangerous for the system.
FINAL NOTE FOR PLUMBERS
It is important that the overflow pipes are plumbed so that
they are visible for when things do go wrong. For example
I have seen for myself that the overflow is installed to
discharge to a gutter, into the ground, or into a gulley that
is covered.
It is important to see the overflow because then you can
identify any issues, see if a drip becomes a run or there is
hot flow out of the pipe. Water conservation is also important
to everyone. In complexes I have seen that overflow pipes
are installed directly into a 110mm waste stack. The
homeowner will never notice if there is anything wrong and
a compromised system may be running for two years, and
along with that a lot of savings. PA
July 2019 Volume 25 I Number 5