Spray gun or Airbrush connectors

[oipigface]

I bought a new compressor to drive my spraygun, which has the brand name Asturo written on it. The compressor outlet socket is a male  quicklink. I’ve got a connector which fits this, but the other end is 1/4”BSP(male). My spray gun hose isn’t 1/4”BSP(female). In fact, I’m not sure what it is. The leaflet that came with the spray gun says that the gun itself is fitted with a G1/4”m compressed air coupling, so presumably the hose coupling is G1/4”f, but the thread in it looks more like 1/8”. Here’s a photo, showing from bottom to top: male Quicklink; 1/4”BSP(male); end of hose.

I have found a website - www.air-craft.net - which offers a variety of reducers. I know that at the fat end I need 1/4”BSP(female). At the other end, I presumably need a G1/4”m. The website doesn’t mention this spec at all, but they do offer M5x0.45 and 1/8” Male. 

This sort of thing is a nightmare for newcomers. Can anyone help?

 

[Nigel_W]

I was puzzling over connectors for my own compressor recently, so decided to look into this.  I was already aware the size does  not relate to thread diameter, and that BSP threads come in tapered and parallel versions. 

It turns out ISO 228 specifies BSP sizes, and the G series is the parallel thread, and R series is tapered thread.   The article below explains that the nominal size relates to the ID of the steel hydraulic pipe it is intended for, and gives the thread dimensions. 

https://en.wikipedia.org/wiki/British_Standard_Pipe

I'm guessing your photo shows a 3/8" BSP(T) male tapered thread and a 1/4" BSP (P) parallel female connector.  Now I'm off to check what I need myself!

 

 

[oipigface]

11 hours ago, Witch_1 said:

 

I'm guessing your photo shows a 3/8" BSP(T) male tapered thread and a 1/4" BSP (P) parallel female connector.  

 

 

The world of standards is a weird place. The male thread in my photo and the quicklink on the end of it are both 1/4”BSP. The thread is parallel. Checking the size of the thread reveals that the actual diameter of the ridges is 1/2”. It apears that back in the mists of time when people made pipes for boilers out of cast iron, the maximum internal diameter of a 1/2” (od) pipe was 1/4”. Now that pipes can be made from other materials the id can be greater. So this fitting has the same 1/2” od as a cast iron pipe, but a larger id. Why the BSI keeps calling them 1/4” pipes when there is no significant dimension that size is anyone’s guess. The technical term is Nominal Pipe Size, and as the name suggests it refers to the internal size of the pipe rather than the fitting, which in the case of 1/4”BSP has 1/2”diameter threads (19 threads per inch).

There is quite a bit of detail about these matters at www.sumidacrossing.org/Tools/Airbrush/AirbrushHoses/ConnectorStandards.

The proprietor of this website has a model of the Tokyo railway sytem in his basement, so his sanity may be questioned. Nonetheless, he casts some light on G1/4”, which is what the manufacturer says is the hose fitting on the spray gun. According to the train nut: “You’ll see the term 1/4”G used on a number of airbrush hoses and similar fittings, and what it means is 1/4” BSP.” ......

Well, that’s not what it means to whoever wrote the description of my spray gun. As the photo shows the fitting is about half the diameter of the 1/4”BSP. Could it be 1/8”? And given that 1/4” in the crazy world of pipe standards is not 1/4”, how could one tell if it is 1/8” or something else?

[Nigel_W]

Looks like 1/8 BSP is a common size in airbrush fittings.  If your hose is an airbrush hose, it may have too much pressure drop when used with a spray gun.  Worth considering a bigger hose with 1/4 BSP each end, instead of an adaptor?

My SGS compressor has a similar quick link to yours, with the female quicklink on the compressor and a male one on the spray gun.  I am considering getting a different spray gun, so I need to ensure it has a female 1/4 BSP thread to screw the male quicklink into - helpful conversation thanks!

 

[Steve J]

@oipigface  Is there a toolstation or similar near you? If so, I would suggest popping along to them with the bits.

Steve

[oipigface]

 

I’ve been to a local tool hire/sales place, who didn’t have a clue. Everything they had there was 1/4”BSP. They suggested I try the milking shed engineers over the road, who had a wider variety of fittings, but not any that fit. It’s quite a way from where I live in rural Dorset to any kind of major chain except Axminster Tools, who sell hoses that look a bit like mine, but not any suitable connectors.

I’m slowly warming to the idea that the mystery fitting is 1/8” BSP, despite the manufacturer’s claim that it is 1/4”. I came across a site (valvesonline.com.au) that lists detailed dimensions of standard threads. The minor thread dimension of 1/8”BSP is 0.3372”. I just measured mine as 0.345, which allowing for wear and other sources of error seems close enough to me. Could it be that the manufacturer made a printing error?

 

[Bobbyr]

http://www.threadandpipe.com/

           check here john , I have used them many times all be it on bigger compressors , they may have what your looking for though .

 

                               Bob

[oipigface]

I have finally got a reducer that works!

I was right: the mystery fitting is 1/8" BSP, which has major diameter (largest diameter of the male thread) of 1/4".  Unfortunately, I got one with tapered instead of parallel threads, but it still works well enough  to deliver MUCH more pressure than my defunct little compressor. Parallel fitting is on its way from ebay.

This doesn't resolve the question of which is wrong: the manufacturer's instruction leaflet in describing the fitting on the spraygun as G1/4"m; or the idea (which I've seen in several places) that G1/4" is equivalent to 1/4"BSP....

......But the machine works, so who cares?