Expansion Valve Discharge Pipes on Solar Water Heaters

By: Hills Solar  11-11-2011
Keywords: water heater, solar water heater, solar system

SANS10254 calls for the discharge pipe from the Expansion Valve (EV –normally attached to the Pressure Control Valve) to be discharged to the outside of the building,to be visible and also not to be placed where the water discharge can cause a nuisance.  (There are other requirements as well.  See the SANS10254 for full details.)

Geyser installers have generally used a Polycop pipe to discharge the water from the EV and they run it into a gutter or out through the eves.

All high pressure geysers require an EV and it is normal for them to vent water every day.  However,with solar installations,due to the greater heat and therefore expansion variations,the fitting and positioning of these pipes require greater attention to detail.  In general,the EV will discharge more water from a solar system than from a conventional electric geyser.  If the system goes into stagnation,the expansion from the steam in the collector can also cause the pipe to vibrate as the EV opens and closes,even causing the pipe to pull out of its discharge position and into the roof if not properly secured.

It is extremely irritating not to mention costly to be called back to an installation for a minor issue such as this pipe.  For this reason we would encourage solar water heater installers to attend to the following when installing the EV discharge pipe.

  1. Discharge the pipe in an area that will not cause irritation to the homeowner,preferably harmlessly discharging the water into a flower bed so that the water is not wasted.
  2. Secure the Polycop pipe firmly to prevent it retreating back into the roof and discharging on the ceiling.
  3. Tell your client that the EV may discharge more water than they are used to,up to a few liters a day due to the greater heat and expansion fluctuations with solar.

Should you receive a call from a client about the amount of water being discharged,ask them to run a hot tap for about 1 minute.  If the flow of water continues it may indicate a faulty valve.  If it stops,the valve is probably working normally.

Keywords: solar system, solar water heater, water heater

Other products and services from Hills Solar


Protect That Pump | Go-Solar

The pump is always installed on the flow side of the solar loop and should have a non-return valve fitted between the pump and collector. If the system is in stagnation due to a power failure or water supply problem,poor quality pumps will not withstand the resulting heat. Adhering to these guidelines and using a good quality pump with a brass housing should ensure many years of trouble free service.


Retrofit Systems | Go-Solar

These and a number of other useful technical issues are dealt with in our one day solar water installation training course and are taken from our installation manual supplied with the course. Teeing out of the cold water inlet pipe to the geyser and in again at the hot water outlet pipe is very low cost and simple but results in the same problems as with the Banjo valve.


Stagnation Protection | Go-Solar

Some controllers such as the SR868C8 used by Go-Solar in our solar water heaters,manages the collector temperature to try and avoid stagnation but still has an upper tank temperature limit beyond which it will shut down circulation. This results in a rumbling noise but more importantly,should the super-heated steam come directly into contact with the inner tank of the hot water cylinder,premature deterioration of the tank may occur.