Humbrol (or similar) mini spray gun

[Atlantic 3279]

I got one of these years ago and similar ones still seem to be on sale today. The size is such that the Railmatch paint jars are a direct screw fit into the cap, and there's just one trigger action, though both the paint jet and the air jet positions are adjustable. I just wondered if anybody with a similar fully-working item can tell me the size of the hole in their paint jet. Following clearance of a blockage mine won't spray at all now, not even thinners or water, and as I've got PLENTY of air blasting out of the air jet I'm just wondering if over-enthusiastic clearing has enlarged the hole in the paint jet beyond some critical size?????????

I won't say what I think should be done to makers of paint that contains badly ground or poorly dispersed pigment.

[Belvoir]

Just measured an old but rarely used example - the jet orifice is 0.75mm diameter.

I suggest that the jet has become vertically displaced -I aways seemed to re-assemble them with the jet a turn too high !!

[Atlantic 3279]

Thanks, I'll re-try the jet height to see if I can coax it into action, but gosh, that paint jet orifice dimension you've quoted sounds awfully large. Even when my sprayer was new and working perfectly I can only remember at most being able to get a strand or two of the very fine wire from thin "multicore" to pass through the jet orifice if I had to clear a stubborn blockage. Can you (or anybody else) please confirm that figure for my peace of mind?

[jwealleans]

I'm sure I used to clean mine with thinner wire than that - .45 or possibly even .33 sounds more like it.

[Belvoir]

Just to make sure - we are talking about the device currently marketed as the Badger 250-3, which has previously been sold under the Humbrol ( and probably other ) brand - yes???

That being so, I have re-checked the orifice - the shank of an unused 0.75 mm twist drill goes all the way through and that of a 0.80 mm does not.

As far as I am aware, the example measured is as purchased.

Happy painting ............

[Atlantic 3279]

I've not lost interest, just been busy for last two days

I haven't yet seen the 250-3, although the 250-2 looks similar yet not identical to my offending Humbrol item which is this:

Even after clearing it out the hole in the paint jet it is no more than 0.4mm max, but I'm sure it was originally smaller than that yet sprayed well, which it wouldn't do at all on monday evening, and there's plenty of air getting through, as I said earlier

[Belvoir]

Atlantic 3279 -

That is a very different device to the one I measured - disregard posted information........

Sorry about that !

Best Wishes

Belvoir

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Edit

The one I have ( modern version ) can be found here

http://chronos.ltd.uk/acatalog/Chronos_ ... s_253.html

I cannot post a photo - no digital camera.

End Edit

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[chaz harrison]

I doubt if the diameter of the nozzle is to blame. When I was an art student we used to use a little device which we called a mouth spray. This was basically two pieces of tube held with a hinged joint. The joint held the tube ends close in an "L" shape. You put one tube in paint or ink and blew hard through the other. A fine(ish) spray would result, but not as good as an airbrush. As I recall the harder you blew the better the atomization. The point is the tubes had an internal diameter of about 1.5 to 2mm.

If those metal parts unscrew why not try leaving them overnight in a screw top jar with some cellulose thinners. This will soften any paint build up.

[Atlantic 3279]

I'm convinced there are no blockages in the paint pick-up pipe or the paint nozzle as I can see ample daylight through them. Investigating this problem further is on my "to do list", originally for tomorrow - although that looks a bit optimistic now! I will however get around to it sometime......

[Atlantic 3279]

Still no joy with this sprayer! I had another play with it today. At first I thought I might have found the problem, as I observed that the breather hole in the cap (that should allow air into the top of the paint jar to maintain atmospheric pressure) was very much reduced in size by paint build up, so I cleaned it right out with a drill bit until I could see the clean sides of the original hole inthe plastic. Unfortunately, that didn't solve the problem. Again I've tried screwing the paint jet up and down, and the air jet back and forth, to no avail. I then noticed that I was getting just a hint of spray as I released the trigger at the end of a burst of air, and wondered if I'd created too fierce or too ragged a jet of air by over-cleaning / over-enlarging the air nozzle. I tested this theory out by reducing the hole size in the air jet with an application of super glue, drilling this out to a smaller size when it had set. Still no good. I finally tried further enlargement of the paint nozzle but that was still not the answer.

As I think about this at the moment I'm more and more strongly inclined to think that over-enlargement of the paint nozzle could in fact be the killer factor here. I'm comparing this "bottom pick up" sprayer to the principle of a hydraulic jack, i.e. PRESSURE = FORCE / AREA.
A small amount of force has to be applied (as a long stroke) to the handle of the jack, this acts on the small surface area of a narrow but fairly long cylinder of fluid in the jack, displacing that fluid and increasing the pressure throughout the fluid in the jack. This fluid pressure acts on the large surface area of the load-lifting cylinder of the jack, creating a large lifting force, but which only lifts the load a very little. The paint sprayer I suspect works in the same way but "in reverse". A small pulling force created by airstream above the small paint jet is enough to reduce the pressure sufficently to draw paint through, providing the pulling force has to act over only a very small surface area. But if the paint nozzle is large then the force created by the airstream creates very little (too little?) pressure reduction to pull the paint through.

[badwolf]

If you go to Machine Mart they do a very good dual action airbrush for about £23, its very similar to a Badger but less than half the price and spares are readily available , they are excellent value.

[Atlantic 3279]

Thanks, I'll bear that in mind, although I may with any luck have access to an even cheaper solution to my problem. A friend of mine thinks he may still have a never used Humbrol sprayer, same as mine, going free if he can find it.