Chilla's thread on air in his/her system has me in a quandary. (And I didn't know that quandary had that second 'a' either...) Q: Stored water pressure equates to about 1 bar pressure per 10 metres height? So if you had a combi boiler fitted on your ground floor and rads on the top one - which could easily be 10m higher - and your started filling up yer system aiming for the usual 1 bar pressure, these top rads would not fill (at 1 bar pressure)? If so, what is the solution here - to simply increase the system pressure to a higher level? And if so, what max pressure would be deemed acceptable? Chilla has his/her pressure at 1.8bar to cope with their 4-storey hoosie but seems to be having air drawn in even tho' it's a sealed & pressurised system. Is it stupid to think it's possible that air could be drawn in on the 'lower pressure' top floor through a poor joint when the pump is running? (Would a useful experiment for Chilla be to try and tweak the pressure up a further notch to, say, 2 bar and see if that stops air coming in?)
Hi, The boiler position has to be taken in to account with this, the boiler needs a certain pressure to operate. Refer to my observation about cavitation, low pressure on the inlet side of a pump, causes cavitation, ie airated water. Regards Peter
Cheers, Peter. There's no issue with lack of pressure in this case - the combi is near the ground floor and showing a 1.8 bar system pressure. What I was wondering is, if you were to stick a pressure gauge into a pipe on the top floor, it would read a lot less than this, wouldn't it? Does that have to be taken into account when deciding on the system pressure? Ie - if the system was pressurised up to 1bar - a typical setting - then on the top floor of a 4-storey hoosie it could be as low as, well, zero...? You open a bleed valve and air could get drawn in. Or am I nuts?
This has made me think as well. I always think of 1 Bar as 1 "atmosphere" pressure, which would support a column of water about 30 ft high (or a column of mercury about 1000mm high). So - if you have a house where the highest radiator is (say) 60 feet above the filling loop of the boiler, and you pressurise at the boiler to 1.5 bar (say) then that top radiator will never get any water. In fact you could take the bleeding screw out (pardon the expression but I think it is correct) some air will come out but no water. Only radiators at 45 ft high or lower will have water in them. So Chilla may have a problem with a high radiator "on the cusp" of not being filled with water so I could imagine it picking up air. I need to slepp on this a bit more... diymostthings
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