DHW expansion vessel

[Richard Russell]

The expansion vessel on our hot water circuit (*not* the boiler expansion vessel!) is supposed to be pressurised to 3.5 bar but is currently down to just over 2 bar. I'd like to pump it up but I couldn't get anywhere with a bicycle pump - it could be I'm just not strong enough.

We've got a perfectly good electric car tyre pump, but the problem is that it can draw up to 10 amps or so, and I've no suitable source of 'portable' 12 Volt power (and no I'm not going to take the battery out of the car!).

Any suggestions for how best to tackle this? I'd be happy to buy an inexpensive 240VAC to 12VDC power supply since it could have other uses, but I've not found one capable of delivering that kind of current at a sensible price.

Richard.

[Davey]

pumped up with air where it is convenient, and then taken to where it is needed, and connected to the tank via a hose with a fill valve. These are sold in American versions of Halfords, but I don't know about here; but it would do your job.

[Andrew Gabriel]

tyre pump in it, which would probably work for this. It works well on the car tyres, but many of the current ones available are very poor quality and contain fake batteries (much lower capacity than is marked on them).

This thought has gone through my mind for my own central heating expansion vessel which is mounted too high up to use a foot pump, although so far (10 years old), it's never needed pumping up.

[Richard Russell]

Yes, I considered that, but they seem to be around the GBP 100 mark which is quite a lot to pay when I have no need for it as a jumpstarter (we have two cars so if necessary I've always used one to jumpstart the other).

Richard.

[Davey]

I didn't find the Air Can, but Halfords offer this:

[John Williamson]

Get yourself one of the cheap jump start units from Halfords or Maplin which either has a compressor built in or (cheaper) just has a cigarette lighter socket fitted to it. They come in handy for all sorts of occasions where you need a portable 12V supply with a bit of poke. Some of the dearer ones even have a smallish 240V inverter built in.

[John Williamson]

? I paid about forty quid for one with a built-in compressor recently. I've never used it as jumpstarter, but it's dead handy for testing 12 volt items, and the light comes in sort of handy now and again, as does the compressor.

[Peter Parry]

Any reasonably sized modern ATX computer power supply should do it, for example :-

that a foot pump such as the one below but you will probably have to find a length of pressure pipe (flexible or copper) to extend the hose.

[Richard Russell]

From where? A quick search doesn't find anything cheaper than about GBP 75, although I must admit that's not too bad for such a versatile product. I worry about Andrew's comments on the quality of the battery though.

Richard.

[John Rumm]

I picked up one from Makro a few years back. 12V jump start, light and a small (150W ish) 240V inverter built in.

[John Rumm]

TLC have a few at different current ratings... a middle spec one:

that, get a 12Ah SLA better from CPC and small charger for it.

[Onetap]

It's knackered, buy a new expansion vessel. And the pre-charge pressure is with no water pressure on the other side of the diaphragm.

[John Williamson]

the latest version of the one I bought. The inverter costs twenty quid extra.

[Richard Russell]

s with no water pressure on the other side of the diaphragm.

Actually it doesn't seem to make much difference. I shut off the water and opened taps, and the pressure measured at the valve on the pressure vessel didn't change by more than a PSI or so.

Why do you think it needs replacing?

Richard.

[Andrew Gabriel]

They may be fine, but beware...

[Roger Mills]

stand about 60 PSI for a short while - and use a hose with a tyre valve attachment both ends to connect it to your pressure vessel.

[newshound]

if the washer and hose are OK.

[Richard Russell]

loads to consider, so the 3.3V and 5V outputs are likely to need dummy loads before one can make use of the 12V output. More info here:

[John Rumm]

Some of the light weight plastic ones have a hard time getting there though... there is so much elasticity in the pump that you get to the point where even a full length stroke can't actually get any further air into the tyre.

[Alan Braggins]

Borrow a better bike pump. 3.5 bar is fairly soft for a road bike tyre.

(If the vessel is in a very awkward position, a track/floor pump with a decent length hose might help, and you might have to brace it against something other than the floor. You shouldn't have to be very strong though.)