Steam Raising Blower

[Peter BellParticipant @peterbell11509]

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

[Peter BellParticipant @peterbell11509]

[MichaelRParticipant @michaelr]

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

[Clive Brown 1Participant @clivebrown1]

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.

[Philip RoweParticipant @philiprowe13116]

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

[Brian Baker 2Participant @brianbaker2]

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

[duncan webster 1Participant @duncanwebster1]

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

[Peter BellParticipant @peterbell11509]

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

[Harry WilkesParticipant @harrywilkes58467]

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

[Chris GunnParticipant @chrisgunn36534]

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

[Peter BellParticipant @peterbell11509]

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

[Grindstone CowboyParticipant @grindstonecowboy]

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

[Peter BellParticipant @peterbell11509]

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

Peter

[Brian Baker 2Participant @brianbaker2]

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

[Peter BellParticipant @peterbell11509]

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

[bernard towersParticipant @bernardtowers37738]

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

[Bill DawesParticipant @billdawes]

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.

[Brian Baker 2Participant @brianbaker2]

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

[Peter BellParticipant @peterbell11509]

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

[Paul LousickParticipant @paullousick59116]

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.

[bernard towersParticipant @bernardtowers37738]

Yes fine pm me

[Peter BellParticipant @peterbell11509]

Just pm'd

[J HancockParticipant @jhancock95746]

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

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

[Chris GunnParticipant @chrisgunn36534]

Bill, thanks for the info on blades, I went to a lot of trouble to make a 6 bladed impeller with forward facing blades, and after 2 or 3 outings it collected enough soot to make it vibrate, bits would break off and jam it. At rallies it whined so much that folks would shout "all clear" when i switched it off.

I adapted a central heating exhaust fan in a tenth of the time, and it is much better. British gas service engineers are replacing these daily, so if you know someone on a maintenance contract, get a request in early.

Chris Gunn

[Bill DawesParticipant @billdawes]

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.

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