3010207c__Apricus_vs_Hills___ClearChain__Difference
[Hills] Supplied Caleffi 250 series [Apricus] Not Supplied [Comment] The steam relief valve was certainly an interesting point when comparing the differences. Hills use the Caleffi series valves (http://www.caleffi.com/en_IT/Technical_brochures/01133/01133.pdf). As noted in http://www.ata.org.au/forums/topic/apricus-or-hills-evacuated-tube-solar-hw-system these valves are designed to work with gycol and are not Potable (drinkable) water rated. The other interesting point is the the maximum temperature rating of the steam valve. Max temp is 180 degrees. Pure water turns to steam at 100 degrees. However it’s under pressure in the collector. Hence in order for steam to form it must be hotter than 100 degrees. On a hot day I can understand 180 degrees being met quite easily. This as indicated in the link can melt the steam valve. 1. They are not potable water rated. 2. They will fail due to scale buildup in the fine hole. 3. They will melt as the collector can reach 190oC 4. They will dump as much as 20L per day in steam, a fact that Apricus is raising with Australian Standards as system are not allowed to dump excessive volumes of water as a means of dissipating excess heat as outlined in AS2712:2007 “no-load” clause 7.4.3 and test methodology in Appendix F. [Difference] 
Steam Relieve Valve
Solar Hot Water - Evacuated Tubes - Apricus vs Hills - ClearChain
Difference