Cross Compound Air Compressor

[gamh44]

All

I would like to build a couple of 8.5" Westinghouse Cross Compound Air Compressors for a 5" gauge loco (N&W S1a). I would like a good representation of the real deal but will settle for whatever can be done to come close.

Having searched this forum, I found a reference to the work up outlined at the Nelson Locomotive Works page (http://www.nelsonslocomotive.com) and although the scale is 1.5", the detail appears to be very good. Most importantly, the end result was a working air pump.

I have started on redrawing all the components as outlined at the NLW page, with the intention of firstly making sure they all fit together (in the drawings) and secondly to scale everything back to suit the size required, which is actually around 10.4:1. A couple of images of the progress are included below. There is still plenty more to do to complete the drawings.

The aim of the exercise will be to end up with a working compressor. I am thinking that the first one could well end up needing a fair bit of modification (e.g. cylinder size, port sizes, valve sizes) to operate efficiently so it could well just end up a passenger or maybe converted to a donkey pump. The engine probably doesn't need two air compressors! As a last resort, these will both just be ornaments, but why not attempt to make them go.

There will no doubt be a heap of questions as this progresses. The NLW design uses off the shelf check valves which are not available here so I will have a go at designing some.

So, I suppose the biggest question at this stage is what obstacles are likely to appear from nowhere? For example, is there anything that should not be scaled back as much as the remainder of the sizes, like the port sizes in the head.

That's about it for now. I'll post some more drawings as they progress.

Regards


Geof

[KarlKobel]

I have a three part pdf from Westinghouse.

I just need to figure out how to post it (each part is >1.5M)

http://www.karlkobel.com
Karl

[John.can]

Is yours full size drawings or scaled down? If so I'll send a pm if you can email them because I'm also looking to build the same compressor for my ten wheeler.

[Dan_M]

The 3 parts Karl was referring to can be found here at bottom of page.
http://www.grandscales.com/freestuff/fr ... index.html

Dan

[Trainman4602]

Hi Geof

The following statement is not intended to discourage you from attempting to build a working cross compound air pump but to give you some sort of idea as to what to expect in taking on a project such as you are suggesting.

There are air pump that have been built and work. Work that is the big question. They my work but how reliable are they. On my K4 I have a Moe’s Locomotive works air pump. It may look like a “Cross Compound” But in fact only the air side is compound. The steam side is simple. I recently rebuilt my pump. I completely disassembled it and documented all the dimensions for future reference.

When new this pump will pump 160lbs of air all day long. One time it pump up to 200lbs pinning the gauge.

It has a slide valve main shuttle valve and that usually is the hart of all the problems. That sticking valve.

I know there are people on here that will say they have a good working pump, but they forget to add how reliable or un reliable it is.

I don’t know you and I don’t know your machining ability. These pumps are finicky to say the least. They have to be perfectly concentric as you have three different sections to loose tolerance too. These inaccuracy will cause binding and stop it from working.

Lubrication is a big factor. If you use 600W steam oil in the steam side it will clog the small ports in the shuttle and pilot valve until it gets hot. The air side is difficulty to lub. If oil get into the tanks it will screw up things . An oil separator is needed. How big? Not big enough.

To add to your problem you are attempting to build a 1 inch scale pump Good luck with that. I ½ scale is borderline for a good working. The Moe’s pump is actually larger. 1.7 I have problems with it. My true scale working air brake system needs to operate on 60lbs of air and I maintain 160lbs in the main reservoir. I only use the steam pump when running light I have a good 12V compressor that easily keeps up with the demand.

I fully encourage you to try to build one. I have been working on a design for about 50 years no lie. I still haven’t come up with a good reliable design. I am close and hope to start the prototype soon.

By the way. I have built larger air pumps with great success. It seams that 1 ½ scale is the borderline to make them work continuously.

I have posted a video of the Moe’s pump in action. You can see the gauge rising. I just can’t rely on it for brakes. Sound great though.

Good Luck Dave

The first part of the video features the pump.

https://www.youtube.com/watch?v=ORaJLMZmQvg

[Bill Shields]

I am totally with Dave on this.

Getting a working cross-compound of the scale you are asking is going to be a major challenge.

Drawing / designing is one thing...

Getting it to actually WORK is going to be another Mt. Everest.

Tolerances are going to stack up against you at room temperature and be impossible to maintain at steam temperatures.

[gamh44]

Karl and Dan

Thanks for the reference to the Westinghouse information. I have this and a couple of other Westinghouse publications that have been very useful. John.can, do these help you? Most of the other drawings I have are similar to these.

Dave

You have provided some very timely advice. I am certainly aware of my likelihood of success and will consider a double acting (rather than compounding) pump from the outset. Or at least plan to be able to revert to this at some later stage. As I mentioned above, I could just end up with couple of ornaments!

One thing I hadn't considered is the (large) oil separator for the tanks. I'll file that one away for sure. A 12V compressor also sounds like a good option. And your video is just sensational. Certainly sounds that part.

I still have a number of components to model so at least there is some drawing practice.

With the sticking valve, I wonder if it would be possible (or plausible or even beneficial) to mechanically connect the HI-P Steam piston to the main valve, rather than going via the reversing valve?

Anyway, off to the drawing board ....

Regards


Geof

[gamh44]

Getting it to actually WORK is going to be another Mt. Everest.

Bill, thanks. Yes, it appears work and more importantly work may well be very challenging. I've not spent too much time on this yet, apart from searching for detail on how is could be done.

Out of interest, are there any castings for this pump in 1" scale. For display only, not operation. Not giving up yet but will need something to fill the XC Pump sized hole!

Regards


Geof

[Bill Shields]

I am not aware of any dummy castings for this.

considering the ease with which you can model / print things these days, if you can make a good 3d model you can get Shapeways to spit you out something that looks good.

Andy Clerci (many years ago) built a Yellowstone that I BELIEVE had a pair of non-working dummies up front where you could see them.

[little giant]

Shapeways already has them for sale in 1 and 1 1/2 scale.

[Loco112]

The CC pumps perform great when built in about 2.5" scale.

When you get to scale brakes, they work in 3+3/4" scale, but 5" would be the lowest I would want to try.

[Asteamhead]

Dan,
Many thanks for posting that link to download the rich PDF manual of the 8 1/2 Westinghouse CC pump!
Geof,
For we built / are still building our N&W locomotives for 5 ", scale 1 : 10 (!) we are strongly interested to have reliable working scale CC pumps, too. With the Y6b there are two working CC pumps totally built from scratch. Yet there still is a bottle for compressed air as backup ...
Dave,
Watched your video, great!
For my german decapod of scale 1 : 10, too I built a 'Tolkien' standard air pump back in 1973 (!).
Steam is working as single, air as compound like the prototype. It worked reliable for many a year and fed the locomotive air brake. Piston valve arrangement is of 'Peter' design, where the piston-stems were made accessable from the outside. Look, the latter (minor) modification is possible with the CC pump, too!

Now I am constructing simple patterns for building another four pumps by use of rapid prototyping.
The complete valve arrangement is intended to be built conventionally due to it's complexity yet.
Not to forget the critical inlet air valves. Balls won't work reliable!
Yes that's an extremely demanding job with many an hour of trials, being well aware by experience!
In case they won't run as intended the bodies will look fine anyway.

Best luck
Asteamhead