Steam raising blowers

The firebox of a Station Road Steam Stafford class miniature steam locomotiveThe purpose of a steam raising blower is simply to create a draught of air through the firebox to keep the fire burning brightly when it is first lit.  Once the boiler is hot and steam pressure is available the steam from the boiler will be used to create the draught.

The photograph shows the driver's end of the Stafford's boiler without (left) and with (right) the grate and firebox cover plate fitted.  As explained on the page about boilers the grate is halfway up the firebox, and the cover plate has the firebox door at the top (closed in the photo) and an air entry hole at the bottom.  Many locomotives have an adjustable flap (damper) over this air entry hole but the Stafford's run very well without one, which simplifies the drivers work load as it does not need to be adjusted.  The air that the fire needs to burn enters via the air hole, flows up through the grate into the fire; and then the hot gasses from the fire go through the boiler tubes (visible in the left hand view without the cover) before flowing up the funnel.  Once the boiler is operating the natural flow of hot gasses rising up in the funnel will draw more air into the fire.  To help things along when the loco is stationary the driver can turn on a jet of steam that flows up the funnel to help pull the air through the fire, and when the loco is being driven the exhaust steam from the cylinders does the same thing.  This has the advantage that the harder the loco is working the more exhaust steam will be going up the funnel, so more air will be pulled through the fire to make it burn even hotter, creating even more steam to let the loco work harder still.  The problem comes when you first want to light the fire, because with no heat or steam there is nothing to pull air into the firebox to burn the coal so the fire will probably go out.  This is why we use a steam raising blower to pull air through the fire.
 
An electric steam raising blower and battery for a model steam locomotiveSteam raising blowers come in many shapes, sizes, and types, and at many club tracks you may even find a 12 Volt outlet wired to each steaming bay to run an electric blower.  Alternatively some clubs (and loco owners) use a compressed air supply to blow air up the funnel (in the same way that the boiler steam is blown up the funnel) to suck air through the grate.  As I never know what I may find when I take my Stafford to other club tracks I always use my own electric steam raising blower which is built around parts of a "Pinnacle Blower" sold by Blackgates Engineering.

The factory Pinnacle Blower is built to run on 12 Volts, so you will frequently see people carrying car batteries around to operate their blowers.  This to me always seemed a bit silly as there are plenty of electric motors that will run for sufficient time to fire up model steam engines while using small and light battery packs.  My conversion has now been in use for over seven years with every steam traction engine and loco that I have owned and the original battery and motor are still going strong.  The photo here (and the one of it fitted to the Stafford shown on the "Firing Up" page will give you an idea of the compact size of the blower and it's battery.

The Pinnacle Blower is normally not suitable for a model the size of a Stafford, but when I purchased it for use with my first traction engine I immediately set about improving it.  At the time I was still employed in the Electronics Industry so I had access to a full range of measuring equipment which told me that as purchased the electric motor drew 0.3 Amps from a 12 Volt supply to spin the centrifugal fan at 3650 rpm.  All I kept of the original Pinnacle Blower was the centrifugal fan and its aluminium case, and even that had the inlet hole opened up to match the inner diameter of the fan and the outlet "tube" section cut off to significantly open up the outlet port.  With a new motor fitted and running from a Radio Control Racing Car 7.2 Volt battery pack, the fan now drew 3 Amps but span at 8000 rpm.  Effectively the blower was now six times more powerful than in its original form, and the small NiCAD battery pack could power the blower for over an hour.  The electric motor that enabled this performance to be achieved came out of my scrap box, but had originally been purchased back in the early 1970's to power a radio controlled boat.  Called a Decaperm it was one of a range of electric motors that were "top of the range" in their day, and has been worth every penny I paid for it.  If you wanted a similar electric motor today it is still available for 116 but I would suggest that you make do with the much cheaper RS540 electric motor priced at about 6.  The RS540 and the 7.2 Volt 3700 milliampere hour NiCAD batteries, plus a suitable NiCAD battery charger, are easily available from many model shops that sell radio control car kits.  The RS540 motor probably won't still be running 40 years after you buy it but you could buy quite a few for 116 !

The other modifications to the blower were an interchangeable funnel adaptor, the black tube is a snug push fit in the copper section to the left of the bright aluminium fan case, a small set of fan blades on the motor shaft (just visible in the photo) to stop the motor shaft conducting too much heat into the motor, and a switch with some high power resistors to allow the fan to be run at a lower speed when necessary (for small models).