Alpha Solar SolaStat-Eco Manuale di installazione - Pagina 16

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SolaStat-Eco Plumbing Issues, Cont.

5. Cavitation.

A pump is used to circulate the water between the tank and the collector.
If the pressure at the inlet or impellor of the pump falls below the vapour pressure of the liquid
being pumped, cavitation will occur. Cavitation in a pump is more likely to occur as the temperature
of the water rises and/or the pressure of the water decreases.
Bubbles form when the water is sucked into the pumps impellor and collapse again as small
implosions when the water is ejected out of the impellor which can be so rapid that a rumbling/
cracking noise is produced (it sounds like stones passing through the pump) and there can be
damage to the impellor and other sensitive components as well as a drop in water volume moved.
Mains pressure solar hot water systems are less susceptible to cavitation than low pressure systems
as the extra pressure will make it less likely that vapour bubbles will form.
As cavitation gets worse, less and less water is moved, often reaching a point where no water at all
moves. Since the solar hot water controller is still reading a 'differential' requiring water to flow
then the pump stays on until the vapour point drops. The vapour point drops either by water
pressure increasing or water temperature decreasing. When the pump is cavitating it may run
continuously for several hours.
To minimise cavitation;
1.
Make sure the pump is appropriate for the installation.
2.
If a variable speed pump then select the best setting (a slower speed that still has enough
head pressure is best as this will create the lowest pressure difference in the pump).
3.
Mount the pump as low as is possible to achieve highest water pressure out of the tank
feeding into the pump.
4.
Lower the resistance to water flow into the pump, such as less bends or more gradual
bends, or wider diameter pipes. Recommended minimum diameter pipe 1/2".
5.
In exceptional cases a larger pump with a larger impellor may need to be fitted to reduce
vacuum at the impellor.
6.
Convert the system to mains pressure.
he SolaStat-Eco controllers have an optional factory setting called 'Pump Timer' to assist in
T
pump cavitation recovery. After the pump has run continuously for approximately ten minutes, it
will turn off for one minute. This cycle is repeated as long as the pump is required to run and will
not affect normal operation in a standard hot water collector and cylinder installation. The one
minute turn off period helps any accumulated air to escape from the pump and has been effective
as a backup in exceptional conditions. This should not be considered a substitute for the afore
mentioned best plumbing practices. This feature can help prevent the pump running for hours in a
'locked up' state, increasing the installation reliability.
NOTE: The Pump Timer is OFF in the SolaStat-Eco-P (Pool) version.
SolaStat Distributor.
19.03-16
Email:
SS-Eco installation 190207.p65