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Posted by Tom on October 12, 2006, 4:21 pm
Please log in for more thread options Andrew Mawson wrote:
>
> > Andrew Mawson wrote:
> > >
> > > > On Thu, 12 Oct 2006 17:30:16 GMT, John Stevenson
> > > >
> > > >
> > > > >
> > > > >Sorry Peter but these don't work as they should because air is
> > > > >compressible.
> > > > >In Andrews case as the furnace tilts it's weight alters and
> > > generally
> > > > >stuffs any load calculations.
> > > > >
> > > > >What you have is an air / hydraulic damper in effect.
> > > >
> > > > John, point taken that the load is fairly large on Andrews
> furnace,
> > > > but I've been fitting these flow controllers on pneumatic
> systems
> > > for
> > > > 20 years and they are very effective.
> > > > If we had a particularly large download with possible shock
> impact
> > > at
> > > > the end I would either use a cylinder with cushioned end travel
> or
> > > fit
> > > > an Ace Linear Decelerator.
> > > >
> > > > I completely agree that air over hydraulic gives a far smoother
> and
> > > > much more linear control, but my thoughts were that this is a
> > > > relatively cheap way to get control where none exists at the
> moment.
> > > >
> > > > Peter
> > >
> > > Now this is VERY interesting ! The two cylinders and valve say
> that
> > > they are pneumatic fittings, but the scrap furnace man that I got
> it
> > > from reckoned that the foundry had been using the cooling water
> for
> > > the coil (pumped round at about 45 psi). Now that gives me two
> > > problems. Firstly it leaks like a sieve - the cylinder end seals
> are
> > > hissing. Secondly, my furnace coolant water is a sealed system to
> keep
> > > air bubbles out - takes AGES to de-air it and is filled with
> expensive
> > > special antifreeze. This furnace body plumbing is done in 15mm
> > > stainless steel pipe and standard compression fittings between the
> > > cylinders and spool valve which I had assumed was to be proof
> against
> > > the odd splash of molten metal. I can see I'm going to have to
> strip
> > > the cylinders and see if they are repairable, I don't fancy oil
> (as
> > > per Johns cunning suggestion) or coolant spraying out at the wrong
> > > time. ( a few weeks ago I was doing a melt when it was pouring
> down
> > > outside, and a single rain drop dripped into the crucible of
> molten
> > > iron - made a very impressive BANG ! )
> > >
> > > AWEM
> >
> > You could, of course, hook it up to your garden hose, after
> > you're fixed the leaks, of course.:-)
> >
> > Tom
>
> Yes tempting isn't it !
>
> I stripped the spool valve to see if I could change any seals, and was
> expecting to find a cylindrical spool with 'o' rings. Instead it was a
> flat surface with ports cut into it, with a plastic shoe sliding over
> them rather in the fashon of a steam engine valve chest, with pressure
> of the air / water / oil etc pressing the shoe in tight contact with
> the face. This explains why it leaks like a sieve at lowish pressures
> and improves at the pressure increases.
>
> AWEM
Cheap power source, over the years I must have built 5 or 6
lifts for friends, powered by mains water supply. First is
still going after more than 20 years.
Since I convinced a friend to automate his glasshouse ventilation
system utilizing water pressure, we have not had to buy tomatoes. :-)
Tom
--
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