Hello Peter, My steam raising fan is nothing fancy, the blades are straight each blade is riveted to a disc attached to the motor

Michael

Edited By MichaelR on 22/09/2020 09:02:23

Many years ago I purchased an ex WD valve cooling blower for i think 5/- from one of those surplus shops on the Tottenham Court Road, remember them? It was a 24volt motor but I only used 12volts, worked very well as a steam raising fan on my 2 1/2" gauge Annie Bodie which was built by my grandfather. One thing that I didn't appreciate was the impeller blade on the blower was die cast metal, after prolonged use partially molten bits of blade were being ejected from the blower outlet. As a 14 year old I did not realise how hot the gases were coming from the loco.

Phil

Chap in our club used the fan and casing from a central heating boiler with 12v motor grafted on

Hi Peter

I used the type of blower Phillip described on my 2" TE worked well but found it prone to shooting up, I now have a larger engine and use a blower as suggested by Duncan mindful of not wanting to raise steam to quickly I use a speed control unit to slow it down. I would suggest finding a suitable motor is the hardest bit once you have the motor you can use anything you have to hand. Fellow club member as a 3 TE and he take the opposite to me whereas I use my blower to 'suck' he uses his to blow just like the steam blower and he uses a 12v camping bed inflator set at 45 deg into a short chimney extension.

H

As an industrial fan engineer of some 60 years some guidance I can offer on blades is that a flat radial is the best blade for handling dirty gases. Backward curved are more efficient than radial or forward curved but do not like dirty gas too much, you get build up on the underside of the blade which will cause out of balance. Of course I say this on the basis of fans in industrial processes fthat are far more arduous than a model loco exhaust so the penalty of using the 'wrong' blade will probably be not too significant for the limited time they are used.

The blades can be pop rivetted, stresses will be very low in an impeller of this size. My company make high pressure blowers up to 1.2m diameter with rivetted impellers.

Bill D.

Yes fine pm me

Another very good source of ready made impellers are scrap, car water pumps.

Right size,shape,weight up to 2.5L cars.

Hi Peter, fan engineering is both a science and a black art. I have always had a saying with fans, if you change something and think it will work it probably won't, or if you think it won't make any difference it will.

Blade type is selected for various reasons, efficiency or application mainly. The ideal is of course the most efficient, especially in these days of ErP regulations (Energy related Products) however sometimes an efficient blade would be not be fit for purpose for some heavy industrial applications. Cost is also a consideration, straight radial blades are less costly than fancy curved blades so as with many things it's all a balance (excuse the pun)

I wouldn't worry about blade type too much, a simple radial blade will give good performance for a steam raising blower, number of blades will be restricted by the space available on a tiny impeller like this, I would probably aim for about 6 blades.

I am talking here about centrifugal fans of course not axials.

The fan casing (volute) converts the energy off the blades into usable energy at the outlet and of course is directional, impellers can also run in a circular housing, probably with guide fans as found on large furnace fans, discharging 360 degrees around its periphery, some losses in performance compared to a volute. The part of the volute where it is closest to the impeller, callled the cutoff, influences the pressure development, too much clearance looses pressure, very close however creates more noise. Again all a bit academic really for this application.

Good luck.

Bill D.