On 25/09/2018 00:14, Rob Wright wrote:
replying to Aidan, Rob Wright wrote:
Honeymonster wrote:
My open vented central heating system suffered from air ingress so I
had it converted to a sealed system.
Check static pressure is adequate for the system. What is the height,
where is
the fill point and pressure gauge?
Any automatic air vents, where are they?
Check system layout. You should be pumping away from the expansion
tank.
Â*Â*The pump generates a pressure difference, PD.
The expansion tank connection is the point of no pressure change, the
pressure change is negligible with the pump on or off. There is a
constant static pressure, SP,Â*Â*applied at the expansion tank.
If pumping away from the expansion tank, the pressure at the pump inlet
will be SP, pressure at pump outlet will be SP+PD.
If pumping towards the expansion tank pressure at pump outlet will be
SP. Pressure at pump inlet will be SP-PD. NB this could be negative at
the pump inlet and for some way upstream, especially at high level. Air
will leak into the system.


I think the above answer is a very good answer.

Its not particularly since it goes to much effort describing the effect
around the header tank - something a sealed system does not actually have!

Many people cannot
understand
that a "pressurized" system can draw in air due to the suction effect
upstream
of the pump.


--
Cheers,

John.

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