Horizontal 3” Boiler Instructions v1.2
Copyright - Chiltern Model Steam Engines
Page 7.
The boiler’s steam outlet valve is situated on top of the boiler and has a 1/4"x40tpi ME connector
which takes 5/32” or 1/8” pipe ferrules. This thread is the same as the inlet/outlet on all Chiltern
Model Steam engines.
The valve is secured in place with a 1/4” brass nut on the inside of the boiler which needs to be
removed before the valve is removed or re-orientated. So to get access to the nut the boiler first
needs to be split by removing the M5 cylinder screw(s), see diagram on page 2. Once the nut is
removed the valve can be unscrewed.
Be careful when reassembling not to over tighten and hence strip the brass threads. Also ensure the
large O ring is in place when putting the boiler body back together.
Boiler Filling
The boiler fill plug screws into the end of the boiler and uses an O ring to seal. It is used to fill the
boiler with water whilst the boiler is inactive, i.e. the burner is not ignited and unpressurised.
Distilled water is recommended, as sold for battery topping up, but clean soft water can be used if
this is not available. Dehumidifier, condensing tumble dryer or even rain water is also an acceptable
alternative, provided that it is adequately filtered for example with paper wine filters. Do not use
demineralised or de-ionised water, as this is not the same as distilled water and could cause long
term damage.
Remove the boiler filling plug and fill the boiler with clean water. There has to be a space above the
water to allow steam to be raised so fill with up to around 450ml of water or empty out 50ml if filled
to the top.
A tube from a garden pressure sprayer or large syringe can be used to fill the boiler. To allow air to
escape while water is being pumped into the boiler, disconnect the steam outlet pipe and open the
outlet steam valve.
Replace the boiler filling plug - do not over tighten.
TIP: Using hot water will reduce the time taken to get the boiler up to steam, hence saving gas.
Boiler Water Level
Care should be taken to always ensure that there is sufficient water in the boiler whilst the burner is
lit. The boiler could otherwise be damaged.
The minimum water level is around quarter full (125ml), hence ensuring the hottest part of the
boiler is always covered by water.
Experience will be gained using the boiler as to how much water is consumed and therefore left in
the boiler at a particular run-time. So when the boiler has cooled pour out the remaining water into
a measuring container – hopefully there is at least 125ml.
From testing with Chiltern Model Steam single cylinder engines a full boiler can be run for 30-40
minutes on light load, e.g. Beam engine ticking over gently. Around 20 minutes under heavier load,
e.g. Mill single running at speed driving a dynamo – see the YouTube videos mentioned above.
