Bruce Napier wrote: > On 16 Jan 2009, at 10:19, Adrian Stott wrote: > >> Why would a more complex (i.e. adjustable) one be needed? > > > If there is no barrier between the air and the water, the air will > all tiptoe gradually away as it dissolves in the water. Hence there > is usually some sort of diaphragm or bladder to stop that happening. > > No matter what the arrangement, the air pressure is bound to reduce > over time from loss one way or another. Thus most accumulators have a > tyre valve in the top so that you can pump it up. > > Because the optimum pressure is either half the pump cut out pressure > or a little less than the cut in pressure (depending who you believe, > and often comes to much the same thing), and because pumps vary in > these pressures, you need to be able to adjust the accumulator > pressure. > > The Cleghorn Wareing ones come pressured to 5 bar, so that you can > bleed off as much as you want when installing. If you don't realise > this, you are wasting your time installing it, as the pump will cut > out long before water starts entering the flask. > > As a final ironic note, having started this thread: after installing > the new pump, and having had to wait to get the new accumulator, when > I came to install the latter, I discovered that the old one was now > performing perfectly. Applying the NB=DF rule, I have therefore > retained the new accumulator as a spare.
RONALERT...RONALERT! ISTR that mine was initially over pressurised with nitrogen and you let gas out until it was at the required pressure. Is nitrogen less likely to escape through a rubber diaphram than air? -- Neil Arlidge - NB Earnest Follow the travels of TNC, now in Ireland http://www.tuesdaynightclub.co.uk/tour.html
