In article 6,
DerbyBorn writes:


The whole system is under pressure either from gravity or from a filling
loop. There is not really a "suck" side to the pump - it is a "circulator
rather than a positive displacement pump

The system contains pressurised water, but partial pressures of
oxygen and nitrogen in the water will be well below air pressure
when the system cools, so it will suck these gases in through any
small leaks, to dissolve in the cold water. When the water is
heated, the solubility of oxygen and nitrogen reduces and they'll
come out as gas bubbles and collect at high points. When temperature
drops again, the partial pressure of oxygen and nitrogen in the water
will drop, and it will suck in more to dissolve. It may seem strange
that air is passing through a leak in the opposite direction to the
water, but that's what happens.

In a heating system, the water leak may well not be noticable, as the
heat may dry the water as fast as it's leaking. To find it, wait
until you aren't using the heating and it stays cold, and then feel
around the pipework and radiator plugs for leaks. If it's a sealed
system, you might also increase the pressure to the normal hot
running pressure, to speed up any leak. (Remember to let it back down
to normal afterwards, and don't blow off the excess via the over-
pressure valve, as you might end up with dirt on the seat, which
makes it leak. Dried crystals on pipework/radiators can also be
a sign of a leak.

--
Andrew Gabriel
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