Steam blowers

[fostergp6nhp]

This is an observation from running my own 4" Foster and observing some other owners and engines on the rally field.
A lot of owners say that their blower does nothing at less than say 50lbs pressure using as much steam as it helps to create, some have even said that is only decoration as it will use so much steam that the pressure drops when using it! A clue to the problem is usually that it is quite noisy in operation. When discussing the subject further with the driver it usually transpires that the blower pipe is just aimed up the chimney with no nozzle in the end. Most frequently the pipe is also rather overscale in diameter as well.
On my Foster i used 5/32 diameter pipe with a nozzle formed by silver soldering a short length of 1/16" bore pipe in the end. It works from 10lbs up and does not empty the boiler.
Food for thought??

[klendo]

5/32" would be about right as the full size is about 1/2"

[jasonb]

Although the diameter reduces by the square route, the volume of steam reduces by the cube route so you need a smaller pipe to get the same velocity of the steam, to get the draw.

Jason

[baggo]

I think the problem with a lot of blowers is that they seem to be an 'after thought' just bunged in the smokebox and are very inefficient, hence the need to wack them open to get any sort of draught. The engine designer may spend a lot of time designing the exhaust draughting arrangements to get the most draught for the lowest exhaust pressure but then puts a bit of bent tube vaguely pointing in the direction of the chimney to act as the blower. The jet probably doesn't fill the chimney orifice (assuming it actually goes up the chimney!) and so creates very little vacuum in the smokebox. Really, as much care should be taken with blower design as with the exhaust nozzle.

John

[albert]

Hello all,
I have a 6"scale Ruston Proctor which is basicly the same size as a 4" Foster.My blower is in the centre of the blast pipe about 1/4" below the top of it and is at the nozzle a 1/16" OD thick wall copper tube.
The blower works perfectly from the time there is pressure in the boiler PROVIDED I control the amount of steam I allow to pass--ie the small pipe at low pressure will consume more steam than the boiler can produce.
Merry Christmas to all
Albert.

[baggo]

The blower for the Allchin is the same arrangement as that Albert. I would imagine it is a good design as the blower jet is bang on the axis of the chimney and being lower than the actual blast nozzle, the diameter of the steam cone when it reaches the chimney will be similar to that from the blast nozzle.

John