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Inherited small models - Air compressor - input valve

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Mark Vincent 117/06/2021 10:46:20
3 forum posts
4 photos

I have inherited several small engineering models from my late farther-in-law. I'm guessing that he inherited them too, so they are probably in the region of 40 to 50 years old. It looks like they run on compressed air and the input valve/fitting looks something smaller than a car tyre input valve. What do I look for in terms of a small air compressor and what is the specification/type/name of the thread on the input valve? It doesn't;t need to be massive, I'm happy to run them one at a time just to see them in action.

If I could work out how to do it I'd ad a couple of pictures.

JasonB17/06/2021 13:00:58
20880 forum posts
2318 photos
1 articles

How to post images

Turbine Guy17/06/2021 13:51:53
369 forum posts
208 photos

I have been very happy using the Master TC-20 airbrush compressor to run my models. It is readily available in the USA at a reasonable cost and works well with small models. If this is not available in your area, something similar would be a good choice.Master TC-20

Edited By Turbine Guy on 17/06/2021 13:56:13

Ady117/06/2021 13:52:08
4562 forum posts
699 photos

It looks like they run on compressed air and the input valve/fitting looks something smaller than a car tyre input valve.

high pressure presta valve, for racing bikes?

Edited By Ady1 on 17/06/2021 13:52:26

Howard Lewis17/06/2021 16:16:06
5036 forum posts
13 photos

Giving dimensions and pitches, in both Imperial and Metric units would help to identify the thread.

Being a fitting for compressed air, would have expected it be 1/8 BSP which is 0.383 OD and 28 tpi.

A Schrader valve would be just a little smaller in OD, 0.305 x 32 tpi.

According to Google, the Presta H P cycle valve body thread is 6V1, 6 x 0.8 mm with the thread for the cap being 5V1 5 x 1 mm.

But the thread could be anything that took the fancy of the person making it!

Might even be ME , 40 tpi thread, or 32 tpi of wjhatever size seemed suitable.

You need the dimensions!


Mark Vincent 119/06/2021 11:45:40
3 forum posts
4 photos

Hi, thanks for the information and questions so far, clearly more complex than I first thought. I have added 4 photos here. Three of the models and one close up of the air input. I have checked the other 10 models that I have and the input is exactly the same on all of them. The diameter of the tread is about 6.4mm, which is a quarter of an inch. There are about 7 or 8 threads in 0.2 of an inch so thats 30 to 40 per inch if that helps. Any advice on what to buy to connect them to a small air compressor would be much appreciated.

2021-06-19 11.26.06.jpg2021-06-19 11.24.21.jpg2021-06-19 11.24.12.jpg2021-06-17 10.41.41.jpg

Jim Nic19/06/2021 13:34:27
344 forum posts
200 photos

Hi Mark

Those connectors look to me like Model Engineer (ME) threads, a common thread for steam/air connections in the model engineering world. 1/4" is a common size but beware, they come in 32 and 40 threads per inch.

I use an airbrush hose to run my engines with one airbrush connector cut off and the rubber inner hose pushed over an adaptor similar to these (with some cyanoacrylate and a couple of small cable ties) to connect to the engine.

pipe fittings.jpg

I may be able to help you sort out what you need, where are you based?


SillyOldDuffer19/06/2021 14:10:30
7341 forum posts
1617 photos

Or I run mine on compressed air by pushing suitably sized rubber or plastic pipe straight on the thread. My compressor has a car-tyre fitting that connects to a standard cone shaped converter that plugs into a wide range of pipe diameters.


Screw connections are essential for connecting rigid piping, used for good looks or steam, but rigid pipes aren't necessary for compressed air test runs.


Mark Vincent 119/06/2021 14:18:49
3 forum posts
4 photos

Jim, Thanks for your help. They look about the same. I'll have to attempt a more accurate thread count to get it accurate. Looking at a different model I'm getting 10 threads per quarter of an inch, so that would indicate a pitch of 40 tpi. also it does look like a fine thread. I'm based in Macclesfield, Cheshire.

Howard Lewis19/06/2021 14:52:52
5036 forum posts
13 photos

1/4 x 40 sounds like a ME thread.

So you will need a nut and a nipple (Which you can then solder onto a short piece of pipe ). For low pressures, soft solder may be adequate, although silver solder would be better..

You should quote the size of pipe that you are planning to use, after having checked to see what nipples are available

If you don't want to, or cannot make suitable fittings. they may well be available from suppliers of such things.

MACC Models, or Reeves come immediately to mind, but ther will be others.



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