The reference to a 40hp engine rather than declaration of a cylinder
size might suggest something different to the normal Cornish beam engine
that you would expect to find in that region..
Particularly in the south-west metal mines pumping engines were
described in terms of their cylinder bore rather than horse-power. This
might well be because at the time in that area power, especially for
pumping purposes. was measured in pounds of water raised one foot high
per bushel of coal consumed rather than today's horse-power. The
resulting figure was described as 'Duty' and figures would be declared
in the millions. Lean's Engine Reporter used this method of
power/efficiency computation and a book on the subject was reprinted
during the 1970s.
However, this appears to have been largely concerned with non-rotative
beam engines (i.e. Cornish engines).
It might be that the pumping engine in question was a rotative beam
engine or perhaps even a horizontal engine. The 1850s, and region,
probably supports it being a Cornish beam engine but there is no reason
why it should not have been a rotative machine, or even a horizontal or
inverted vertical engine. It would not surprise me if it was NOT built
by one of the Cornish builders.
As to its size I think you are looking for something rather larger than
a shed but it was probably not exactly in the 'large' category of
engine. If a Cornish type engine then you might be looking for something
in region of 40" to 60" cylinder diameter.
Paul Stephens
-----Original Message-----
From: mining-history [mailto:[log in to unmask]] On Behalf Of
NEWMAN, Phil
Sent: 03 April 2006 11:04
Subject: Engine size terminology
Dear list,
Can anyone help with this?
If a steam pumping engine in an 1850s MJ report is described as 40hp
instead of referring to the size of cylinder or stroke, should I assume
that it is not a standard beam engine that is being described but
something a little more modest? How 'big' is 40hp? Should I be looking
for the remains of a substantial stone building or a small tin shed?
The tin mine in question on SE Dartmoor only reached 18f below adit,
though as always, the site was described as a 'capital speculation' so
the adventurers were no doubt intending to go deeper and would have
needed plenty of pumping capacity.
Many thanks
Phil Newman
(English Heritage Archaeological Investigation Team, Exeter)
http://www.english-heritage.org.uk/server/show/conWebDoc.3249
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