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.
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
The boiler is
lifted out for assesment
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
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
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
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
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