With reference to the mystery saddle-shaped boiler at Oxford Prison, Brian
Durham has emailed me a plan of 1842, and it seems that the boiler was
indeed a water boiler, used to supply hot water by convection to heat
exchanger (like an economiser in reverse) that warmed a hot air and
ventilation system that was fed around the prison in ventilation ducts or
flues. The date of 1842 seems likely for the installation of the system,
given contemporary concerns about 'miasma'. Hopefully Brian will circul;ate
this plan later.
Brian seems to have misunderstood several of the points that I have
conveyed to him by email over the last few days. Re this correspondence, I
wanted to put the record straight, so I have copied my emails to him below,
with the most recent at the top.
Please note that I made several references to 'waggon-top' boilers in these
emails, following Brian Durham's initial description of the boiler to me
over the phone. This was in error and I was, of course, referring to 'wagon
boilers'. The saddle shape was not made clear to me at the time.
From: Rob Kinchin-Smith
Sent: 11 February 2004 11:23
To: 'DURHAM Brian'
Subject: RE: 1842 drawings[Scanned]
The 1842 plans are superb and clearly illustrate the boiler, complete with
a hot water convection circuit leading into a heat-exchange chamber in the
centre of the basement. The convection circuit consists of the hot-water
outlet at the centre (highest point) of the boiler, as well as the return,
the latter branching into the two lowest points of the saddle.
I imagine that the two sets of black / dark grey pipes (the outlet and
return) were connected within the heat-exchange chamber by a series of
(possibly arched) smaller diameter pipes, not shown on the plan. In the
heat-exchange chamber, the heat from the water would be transmitted to
fresh air that was admitted into the ventilation / heating flues (in red /
pink)and circulated throughout the prison, before being expelled from
windows and ventilators in the roof. The circulation of fresh (and often
heated) air was a standard feature of hospitals and prisons at about this
time, as it was then thought that putrid air caused cholera and other such
prevalent diseases of the day. It was later shown that these diseases were
in fact transmitted through polluted water, and these extravagant
ventilation and heating systems fell into disuse, to normally be replaced
by piped hot-water central heating systems.
From: Rob Kinchin-Smith
Sent: 10 February 2004 10:31
To: 'Brian Durham'; Peter King
Cc: [log in to unmask]; [log in to unmask]; Christopher
Subject: RE: Saddle-shaped boiler at Oxford Prison (hold
The air stove or water boiler arguments are sounding increasingly
reasonable to me. The shape of the object does not seem likely for a steam
generator for the reasons set out in yesterday's email to you (below).
Re your understanding of our telephone conversation and my email, you seem
to have misunderstood much of what I said.
The thing about the square or hexagonal bolt heads was a diagnostic feature
of date, not function. Also it is the shape of the bottom of the 'boiler'
that is wrong for a wagon-top boiler (Note: My mistake - should read 'wagon
boiler. RK-S), rather than the top. Re the steam collection space, wagon-
top (wagon) boilers didn't normally need a separate steam collection space,
as the water-level within the boiler was well below the crown of the
boiler, leaving plenty of space for steam within the top of the boiler.
What I said was that in a saddle-shaped 'boiler' such as that in your
photos, the internal water-level would need to cover the crown of the
firebox, leaving very little space for collecting steam within the top of
the 'boiler', unless there some sort of additional high-level steam
collection space (functioning like the dome on a steam locomotive boiler).
I hope that clears things up
From: Rob Kinchin-Smith
Sent: 09 February 2004 17:20
To: 'Brian Durham'
Subject: RE: Saddle-shaped boiler in vault under 1780 prison cell block
Having now seen your photographs, it seems that I have misled you about
the 'waggon top ('wagon') boiler' theory. A waggon-top ('wagon') boiler has
a flat or very slightly concave bottom, rather than the true saddle shape
you have found. The engineering of the boiler, as shown in your photo, may
imply a 19th-century date, rather than an 18th-century one.
I will have to think on on this one, but it is a conundrum. It certainly is
a rare beast, as is any in-situ pre-1868 boiler that has not seen use for
c.150 years. As such it is a real gem, but its small size makes it unlkely
to have powered any serious machinery, except possibly something very small
indeed. A hot water generator seem likely at the moment.
It seems clear that the lower pipe is an inlet pipe. If looks unlikely that
it was a steam generator, as the boiler would distort if the crown of the
firebox were not permanently covered with water. Given this fact, the
(domeless) saddle design leaves hardly any space for the collection of
steam. If it were a steam generator, then there should be a distinct
corrosion line at the working water level inside the boiler and there
probably would have to be an additional steam-collecting chamber, like the
dome of a steam locomotive.
The proof of the pudding should be in the detail. Are all bolts square
headed or are there also hexagonal bolts. Hexagonal bolts would imply a
later date. The red colour of the ashes certainly imply a firebox under the
saddle, but where is the chimney? Steam would be drawn off at the very
highest point of the boiler, where there would probably be a raided dome or
steam collecting space (otherwise the boiler would 'prime', sending hot
water down the steam pipes). A hot water generator could be filled to the
brim however, with water possibly being drawn off slightly lower. Sadly,
much of the detail would have been in the pipework. How much has gone?