Steam Raising Blower

Hello, I want to build a steam raising type blower with a diameter of around 5" driven by a 12v variable speed motor on top.

Designs show various types of blades including straight ones. Has anyone built anything like this and can offer advice on blade construction and attaching the blades? Thanks

Peter

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

I made one about 3" dia. The blades are "L" shaped with a rivet through the short leg. A top plate was added and the assembly silver soldered. I don't think the top plate is essential. My blades are straight radial and seem OK. There's no volute.

The rotor needs to be quite well balanced as they need to go quite fast for efficiency.

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

Greeting Peter, a while ago, ME published a design and writeup for a variable speed blower, which I wrote. It used flat straight blades, which worked well, I used it this Sunday on my A3, and it has had plenty of use, and is one of several at my club. The blades were bolted on, using nyloc nuts, no problems so far. The clearance between the bottom edge of the fan, and the casing makes a big difference to performance. Whilst curved blades are more efficient, the whole blower was designed as a beginners project, to perhaps encourage someone who has purchased a locomotive, to start to make things themselves.

Regards

Brian

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

Many thanks for the advice everyone, I'd never have thought of using pop rivets or a central heating pump! The straight blades makes it easier.

Brian, would apprecciate the details of ME your article was publised in? sounds an interesting read.

Regards

Peter

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

Plus one for a central heating boiler exhaust fan. The 240v motors fail, and it is easy to remove it and fit a 12v motor instead.

I ditched my home made one which sounded like an air raid siren for one of these.

Chris Gunn

Investigated a dead central heating pump but its getting a bit too heavy so coming out in favour of making the Brian Baker version in ME. Hope to track down the relevant back issues.

From a web search it looked like there maybe laser cut plates available?

Peter

Possibly a bit of confusion creeping in here? Duncan and Chris are, I think, talking about central heating boiler exhaust fans NOT the central heating pump (or circulator) which are usually cast-iron and quite weighty. Not all boilers have exhaust fans.

Hope this helps.

Rob

Thanks Rob, Yes your right--thats what you get for reading postings without your specs!

Peter

Greetings Peter, my article was published in ME in three parts, 11th Nov 2016, issue 4547, pg 706, 9th Dec 2016, issue 4549 Pg 852, and the last part 6th Jan 2017, issue 4551 pg 102. It was designed as a beginners project, and many of the parts were laser cut. As it stands, it will be fine for larger 5 in gauge or 71/4 gauge locos, and many parts can be laser cut. I never did get around to a smaller gauge version. I may have a set of parts somewhere for the published version.

I think it's worth reading the article, but I would say that wouldn't I!

Regards

Brian

Thanks Brian. Now located copies had a read, well written and all looks feasible. The size is fine, should be able to get the sheet parts profiled on a cnc mill. Cannot locate a 12v heater type motor at present, I have a few waiting for a project---if only I could find them!

Regards

Peter

Peter, I have a ex Fokker oven fan which is 4.75 in dia x 1.125 tall. It has a 1/4 inch collet fitting all super quality as normal for aircraft stuff. Pay the post and it’s yours. Pic in my album

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.

Thank you for that Peter, "well written" from someone who had to retake English 0 level.

Bill. Thanks for the advice on blades. I have looked at various fans in my life but never really understood why there are so many differences between them whe they are all doing the same job.

This design has 12 smallish blades, other designs have 6 deeper blades, is there an easy rule for efficiency on size and number also from what I have read how critical is the blade face to casing dimention?

Brian, I found the first part really useful where especially where you showed different examples of blowers, I had only ever seen them at a glance without taking a lot of notice!

Bernard, Thanks for the offer which I'd like to take up, shall I PM you?

Peter

Issue 4153, Volume 187 of Model Engineer has an article about making a steam raising blower. (the very first magazine in the digital archive).

Paul.

Yes fine pm me