In the February, 1938 issue of Model Craftsman, there is a construction article by a Mr. L.E. Smith entitled "A Cross - Compound Air Pump" (for 3/4" scale) whose main dimensions were scaled down from a Pennsylvania Railroad No.2 locomotive.
I don't know whether it works or not but all of the drawings are there to make one.
Cross Compound Air Compressor
Re: Cross Compound Air Compressor
DanFender wrote:Geoff,
One other point. My friend who built one of these (successful) 1.6" scale pumps, started out making a true cross-compound pump. But he later realized this was not feasible, and changed it so that the steam side was simple (h.p. steam on both cylinders), with only the air side compounded. This echoes Dave Sclavi's experience.
Thanks - good advice. While I like the idea of attempting a true CC pump, a single, mechanically operated valve to drive two HP pistons is probably at the limit of what at least I can do.
Geof
Re: Cross Compound Air Compressor
CarrdoCarrdo wrote:In the February, 1938 issue of Model Craftsman, there is a construction article by a Mr. L.E. Smith entitled "A Cross - Compound Air Pump" (for 3/4" scale) whose main dimensions were scaled down from a Pennsylvania Railroad No.2 locomotive.
I don't know whether it works or not but all of the drawings are there to make one.
Thanks. I'll have to do a bit of searching for that one - sounds interesting.
Geof
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Re: Cross Compound Air Compressor
Does LSGOD still make castings of his cross compound air compressor? If so please PM me I am interested in getting castings.
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Re: Cross Compound Air Compressor
If I remember right Tom Miller had a pair of working cross compound pumps on his Big Boy. I think they were made in Australia by a fine craftsman in 1.5" scale. This was many years ago so I have no idea if the man is still alive let alone still making the pumps. Any one looking to make a working cross compound pump is in for a very interesting engineering exercise as the guts are very complex. One major problem is the internal push rods which in 1.5" scale are tiny in diameter. There are other issues. Barry Haig had a full size one on a pallet decades ago and was working on solving some of the problems but never put one out. Others have tried.
Cary
Cary
Re: Cross Compound Air Compressor
Hi,
All of the replies started me thinking a bit more (I've found that can be dangerous at times) and because of having to start this thing up from room temperature you really need a thermally controlled valve on the pump body near the steam inlet so that steam gets bled off until the steam side of the pump comes up to operating temperature then the valve would close.
I think I know how to make one that works, but sometimes there is a long way between theory and something that actually works. Just another thing to put on my list, but you need these things to take the finikiness out of the beast. It needs to be something you can rely on, otherwise it isn't worth it.
Just my five cents.
Richard Trounce.
All of the replies started me thinking a bit more (I've found that can be dangerous at times) and because of having to start this thing up from room temperature you really need a thermally controlled valve on the pump body near the steam inlet so that steam gets bled off until the steam side of the pump comes up to operating temperature then the valve would close.
I think I know how to make one that works, but sometimes there is a long way between theory and something that actually works. Just another thing to put on my list, but you need these things to take the finikiness out of the beast. It needs to be something you can rely on, otherwise it isn't worth it.
Just my five cents.
Richard Trounce.
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Re: Cross Compound Air Compressor
The pumps that Tom Miller has were reworked by Myself and Dick Bagley, as they would not stay running as built. A new piston valve was designed and the last I know it was working fine. That was in the early 80's and I can't remember just what all we had to do to make them work.
Will
PS: maybe Tom can add something to this. Are they still working?
Will
PS: maybe Tom can add something to this. Are they still working?
Re: Cross Compound Air Compressor
I have a full set of drawings done in the UK by a guy called F. B. Gittins, who was apparently building 4 PRR E6's for a commission in the states to run on 7.5 gauge. I did a bit of research on the guy and was told the l the loco's were very fine scale. The prints are obviously CAD generated so are a relatively modern design at 1.6 scale. I wonder if the locomotives were ever delivered or how the pumps worked ?
Jim
Jim
www.northernsteam.com