Hi Gregory
On (10 Aug 97) Gregory Procter wrote to Alec Cameron...
 AC> Consequently the engine delivers less HP, because it is not the stop
 AC> valve pressure but the difference between SV pressure and exhaust
 AC> pressure, that defines the work done by the pistons.
 GP> We're back to the same problem you had with your washing!
 GP> The energy savings can be appreciable in recovering the waste heat, and 
it
 GP> is relatively simple to provide a flap to exhaust to the open air when
 GP> full
 GP> power is needed.
Yes that is an elegant solution to recover full power. On downhill runs,
that's a version of regenerative braking but without wires!
 GP> The potential big saving with condensing on a steam loco is to not need
 GP> such
 GP> a big water cart, which needs hauling around.
However there has to be good reason why condensing locos were so rare, 'tho
the technology is ancient and the first practical versions ran long long ago.
I suppose that the build up of electrolytes in the water led to accelerated
corrosion. And on a long uphill grind, it may have been a nuisance to suffer
drive power drop as the back pressure increased with the inevitable
temperature rise of the condensate.
                  
 AC> Hence racing cars may have "open exhausts" ie no muffler, hence
 GP> little
 AC> or no back pressure to subtract from the pistons' output. Noisy!
 GP> Not quite! The open exhausts are very carefully designed to provide
 GP> back-pressure at operating speeds. Because the inlet and exhaust valves
 GP> are open
 GP> at the same time, the design trick is to get all the burnt gasses out, 
but
 GP> not
 GP> to loose too much intake air and unburnt fuel.
As I said,  *little* or no back pressure. I guess that the back pressure you
refer to is *little* enough not to cause a loss of useful power output.
Hey, no one else seems interested in this thread. I suppose we need to change
the subject: Sydney trams returned to commercial service this week. But, the
fancy name Light Rail is used. Dunno if the supply is 600v dc, dunno if the
rail shape is compatible with before. There are quite a few preserved working
cars in outdoor museums, I wonder if these veterans will ever join the new
cars for special events??  Cheers..ALEC
... ....Horsepower was a wonderful thing when only horses had it
--- PPoint 1.92
---------------