Spanner Swirlyflo MarkIIIb Steam Boiler

47105 was one of the Class 47s fitted with a Spanner Swirlyflo MkIII boiler. The current boiler in the loco, J3946, was fitted into 47105 during its final classified overhaul at Crewe Works in June 1984. It was fully overhauled and re-tubed at the works and only ran until April 1986, when it was isolated.

47105 at Kirkcaldy in April 1986, shortly before the boiler was isolated

In February 1999 the boiler from 47105 and a spare boiler, which was donated to us by Freightliner, were both inspected at Toddington by our boiler company, who at the time were known as Plant Safety. The donated boiler, which was removed from 47157 whilst on an 'F' exam at Crewe Diesel, was found to be in an inferior condition to the one that was already inside 47105.

Therefore the boiler from 47105 was the one that was sent away to Northern Arc Electric Welding Co. in Braunstone, Leicester for overhaul.
The boiler was refitted in 47105 in December 1999 and fully reinstated in February 2000.

The boiler is lifted out for assesment

Since the reinstatement of the boiler in 47105 the loco has been invaluable in the winter months heating trains alongside the GWR diesel fleet.

The boiler needs to be recertified every year which requires removal or the end doors, steam dome and other inspection doors and gauges.  This can be quite a tricky job as the boiler remains in situ in the loco and space is very limited.

Once stripped the boiler is given a cold test and, providing it passes, all of the parts are returned to enable a warm test. Providing all is well the boiler is certified to steam safely at the GWR

On a 5 yearly basis the boiler needs to be removed from the loco completely for an ultrasonic test. For this exam all removable parts and protective cladding are taken off the boiler as shown below.

The boiler stripped down for an ultrasonic test

So how does it work?

Once the boiler switch is closed , the water pump will run and will draw water from the tank and commence filling the boiler. Once the water level reaches the low water cut -out , the Mobray float switch contacts will energise the burner motor. A fan is attached to the burner which blows air into the furnace to feed the fire. The fuel pump is also driven from the same shaft. The fuel atomiser and electrodes are situated within the burner. The burner is a converter and produces 240V AC which gets stepped up to 10000V AC in the transformer which produces a spark across 2 electrodes which instantly ignites the atomised fuel being sprayed.

The heat produced from the furnace passes through the tubes , heating the water which soon turns to steam. The water pump continues to run until the feed water regulator Mobray float switch is operated which stops the pump running . This float switch operates the water pump accordingly as the level rises and falls.....with the low water cut -out switch shutting down the boiler if for instance , the pump fails or there is insufficient water in the tank. The fluestat situated in the chimney stack will shut down the burner within a few seconds if it cannot detect heat . Under normal conditions when it does detect heat , it will operate to switch off the spark at the electrodes , the flame (now established and kept going by the fuel and air) will continue to burn.

Once the steam pressure has risen to 60 PSI , the pressure switch operates to switch off the burner , likewise when the pressure drops to 40 PSI it will run the burner again.   The safety valve  will lift at  75 PSI .   The boiler  if maintained  correctly will generally ' look after itself ' when running however a careful eye needs to be kept. Water level can be monitered with the side glass and should there be an urgent requirement to shutdown the boiler , this can be safely done with a switch in each cab.

Spanner Mk3b boiler

 At the end of operation , once the steam pressure drops to 10 - 15 PSI the boiler must be ' blown down ' to remove sediment from the water space. This is achieved by opening the blow down valve .Once all the steam has vented , the boiler switch is opened to effect a complete shutdown.


Thanks to A1A Locomotives for the boiler gen.