Set Square wrote:

It best to pump air in with the valves shut, too - and then crack
open a valve and listen to the water being expelled.

But you can't start the process that way as the air's got nowhere to go
(unless you attach an external pressure vessel, which would seem a
little OTT).

What do you use for your air supply? - Foot pump, compressor, ...?

It usually takes several goes. You can tell when the rad is empty -
because the last slug of water/air mixture makes a very rude noise as
it passes through the valve!

I'm just wondering whether this might be a good way of disturbing the
sludge, which inevitably collects at the bottom of every radiator, and
distributing it round the system. That would certainly be a Bad Thing.

Nice idea though.

--
Andy