Typical steam locomotive practice called for air from the compressor to pass through a series of pipes arranged like a primitive radiator before entering the reservoir. Compressed air is hot, but why go to those lengths to cool it? The real question is whether the air side of the pump was ever lagged or insulated.

wrj494@aol.com

> Typical steam locomotive practice called for
> air from the compressor to pass through a
> series of pipes arranged like a primitive
> radiator before entering the reservoir.
> Compressed air is hot, but why go to those
> lengths to cool it? The real question is
> whether the air side of the pump was ever
> lagged or insulated.
I belive the air when it is compressed it give up heat an make to air at 140+ pound work.

Stan


owenpaulsen@att.net

> Typical steam locomotive practice called for
> air from the compressor to pass through a
> series of pipes arranged like a primitive
> radiator before entering the reservoir.
> Compressed air is hot, but why go to those
> lengths to cool it? The real question is
> whether the air side of the pump was ever
> lagged or insulated.

Hot compressed air tends to "caramelize" the lubricating oils within the air which gums up passages and ports in the control valves as well as shorten the life of gaskets. As to lagging, the opposite was the case. Many pumps were cast with cooling fins on the air side to help keep the piston from over heating and freezing up.

Tom

ironbartom@aol.com

As Tom said, the air side of the compressor (other than very early models) usually has cooling fins to radiate heat, rather than being lagged to contain it.

A major reason for wanting to cool the air, is the fact that hot air will hold more moisture than cool air. The air will cool eventually anyway, and this moisture (vapor) will then condense as water, contaminating the air brake system. It is preferred to get rid of as much of the moisture as possible before it gets to the brake system.

The cooling coils are placed before the main reservoir (or between multiple reservoirs) so this water will condense and can be drained from the bottom of the reservoir.

With regard to radiating heat from the air end of the compressor, the heat developed is one of the main limiting factors for how much air a compressor will produce. Steam driven air compressors that are working excessively, such as providing air for air dump cars, have been known to glow red around the discharge valves.

Diesel locomotives also have provision for cooling the air after it leaves the compressor, and often between stages of multiple stage compressors.

I take that back: the only steam driven compressor I can think of that actually has the fins is the Westinghouse 9-1/2", but none are lagged or insulated.

The main reason for cooling the air from the air compressor in radiating piping is to trap the moisture in a known location where it can be kept out of the operating system and conviently drained away. Probably the worst side effect of having water in the main reservoir is that it reduces the capacity of the air brake system progressively as the reservoir becomes filled with water. If the main reservoirs are full of water, then the only air flow available to operate the brakes occurs when the compressor is actually pumping.

> I take that back: the only steam driven
> compressor I can think of that actually has
> the fins is the Westinghouse 9-1/2",
> but none are lagged or insulated.
Thanks for all your responses. 494 has an 8" Westinghouse pump without cooling fins. The steam side was lagged with wood and covered with sheet metal. The air side at some time received a sheet metal cover, but there was no evidence of lagging under it. The cover did not appear original. In putting it back for authenticity, should we replace the sheet metal?

wrj494@aol.com

Was just looking at the book "Minuteman Steam". There is a photo of the modernized 905 (494), but the compressor is on the other side. The other 4-4-0s in that section show compressors with fins on the air side, unlagged. Not mentioned, but another problem with water in the brake system is ice in the winter, not a common problem with steam operation today, but once a real concern.

Thanks for all your responses. 494 has an
> 8" Westinghouse pump without cooling
> fins. The steam side was lagged with wood
> and covered with sheet metal. The air side
> at some time received a sheet metal cover,
> but there was no evidence of lagging under
> it. The cover did not appear original. In
> putting it back for authenticity, should we
> replace the sheet metal?


bobyar2001@yahoo.com

Another way I have seen to create air flow around the air end of a pump is a sheet metal jacket drilled with a number of holes one inch in diameter. The idea is that as the air heats up on the outside of the piston, it rises and flows out the upper holes, drawing cooler air in through the lower ones.



ironbartom@aol.com

> Was just looking at the book "Minuteman
> Steam". There is a photo of the
> modernized 905 (494), but the compressor is
> on the other side. The other 4-4-0s in that
> section show compressors with fins on the
> air side, unlagged. Not mentioned, but
> another problem with water in the brake
> system is ice in the winter, not a common
> problem with steam operation today, but once
> a real concern.
A review of post-1939 photos c.1940s shows sheet metal over the air end even at that early date. Since the Billerica shop crew was scrupulous in their work at the time, that's good evidence that the sheet metal ought to go back and that's what we'll do.


wrj494@aol.com

David;
My 1926 Westinghouse Catalogue doesn't show the 8"
compressor. It does show the 9 1/2"(with fins)and the 11" but for the answer to your question, none of the compressors, single or compound, show any jacketing on the air side. The 9 1/2 is the only one with fins but the 8 1/2 cross compound has a couple of ribs around the low pressure air cylinder. I would be inclined to believe they were for strength rather than cooling.
Jim

> Thanks for all your responses. 494 has an
> 8" Westinghouse pump without cooling
> fins. The steam side was lagged with wood
> and covered with sheet metal. The air side
> at some time received a sheet metal cover,
> but there was no evidence of lagging under
> it. The cover did not appear original. In
> putting it back for authenticity, should we
> replace the sheet metal?


rrfanjim@mvn.net

> David;
> My 1926 Westinghouse Catalogue doesn't show
> the 8"
> compressor. It does show the 9
> 1/2"(with fins)and the 11" but for
> the answer to your question, none of the
> compressors, single or compound, show any
> jacketing on the air side. The 9 1/2 is the
> only one with fins but the 8 1/2 cross
> compound has a couple of ribs around the low
> pressure air cylinder. I would be inclined
> to believe they were for strength rather
> than cooling.
> Jim

Jim, This is a subject which ought to be allowed to rest in peace, but I can't resist adding something further on the subject of this 8" air pump. Artemas O. Wilkins, writing in 1939 of the first rebuild, reprinted in Robert Willoughby Jones' Boston and Maine, City and Shore, says:
"Where was there an old eight inch air pump?...The pump was a sticker. Report had it that a man was told to scout the main and branch lines of the Boston and Maine and not to return to is family unless he brought a pump. He got it, in an automobile junk yard."


wrj494@aol.com

Insulation!

In this thread there seems to be some confusion between the; WABCO "8" (pre-year 1900) single cylinder steam driven air compressor" (that was being scrapped in a hurry by the 1900's) and the much later 8.5" x 150 Cross Compound (twin cylinder) "steam driven air compressor" that is still as good as it gets in the way of steam driven air compressors.

The CC pump is much larger and much more efficient that any of the singles, as it will pump about 3 times as much air on the same volume of steam that any of the later (than the 8")single cylinder pumps (9" & 11") could.

The 8" pump Chris put the picture up could be made into a benchtop cross-compound with the 9 1/2" pump located at the other end of the bench.

Dave Sutter