Extract from 'Central Heating - Fault Finding & Repair'
Introduction
The major cause of system noise is incorrect speed setting.
With the circulating pump speed set too slow the
following may occur:
a) Boiler ‘kettling’ due to water not passing
over the heat exchanger fast enough causing it to become
overheated
With the pump speed set too high:-
a) Unnecessarily fast water flow circulating around the
system causes noise in the pipe work which may
then ‘vibrate’
b) As the water goes around a sharp change of direction
it may cause the pipe work to ‘hammer’
c) At the radiator, the radiator valve seat may start
to oscillate
d) The circulating pump may sound louder if the pump
is mounted in a cupboard or close to floor boards
(with a cavity underneath acting like a sound box)
The solution to these incorrect speed settings is to
adjust the circulating pump speed accordingly or fit
an automatic and fixed speed circulating pump.
Avoiding System Noise
There are some do’s and do not’s to follow
to avoid system noise when installing circulating pumps.
Do not install system pipe work under tension.
Do not install flow and return pipes so they touch as
they expand and contract at different rates.
Do not install sharp bends in the pipe work close to
the circulating pump.
Do not set the circulating pump speed unnecessarily high.
Do use a cushioning material where pipe work is in contact
with joists, beams etc.
Do support the circulating pump with proper fixing brackets
and use the heat resistant rubber between the pipe work
and bracket to absorb the vibrations.
 Impeller Noise
As with any central heating system component there is
wear and tear. The circulating pump will give year after
year of trouble free service but the bearings and rotor
will gradually wear and lose their precision running
ability.This ‘out of true’ state causes
the impeller to run out of balance and create noise which
is evident by the pump slightly moving when operating.
This is a sign the pump is nearing the end of its working
life and the only solution is to fit a new pump.
Air in Pump
When air enters the pump the noise can be very loud.
It is relatively simple to vent the pump but the reason
for the air entering the system must be established and
corrected as dry running/cavitaiton of a circulating
pump will damage it very quickly.
If the pump is installed wrongly or at the wrong angle
the top bearing may not receive system water to both
lubricate and cool it. The pump will fail quickly if
this is not corrected immediately.
Cavitation
This is caused when the inlet pressure is too low on
the suction side of the pump. It occurs when the pressure
on the impeller vanes falls below the pressure of the
liquid causing bubbles to form. When these bubbles flow
to the high pressure region of the impellor they implode.
This phenomena causes noise and can also damage the circulating
pump.
The solution is to increase the static head by raising
the feed and expansion cistern or by converting the open
vented system to a sealed (pressurised) system.
Extract from 'Central Heating - Fault Finding & Repair'
|
