Modelling the Kerr-Stuart Brazil Class 0-4-2ST locomotive in 16mm scale. - Keith Bucklitch
The Fuel tank
This model is fired with methylated spirit - ie. Alcohol. The flow of methylated spirit is controlled by a 'chicken feed' arrangement. As the fluid level in the sump falls, air bleeds into the tank up the air pipe. This allows meths to flow down into the sump until the end of the bleed pipe is covered again. To function properly it is essential that there are no air leaks in the system. Otherwise, the meths will overflow, probably resulting in a fire with potentially disastrous results. It is also necessary that the bottom of the air pipe has a bevel, otherwise surface tension leads to an air block and failure of the spirit to flow properly.
1. The Meth's (Spirit) Tank.
1. The meths tank is made from two pieces of 0.75 mm (22G) brass or nickel silver. Cut the rear piece first to size, allowing 1 mm less on the width for the fold. Cut out the slot for the sight glass and bend to shape. Measure across the internal width and cut the second piece to fit between the sides. Mark out and drill the holes for the control valve, airpipe and filler bush. Allow for the fold by reducing the length of the centre of this piece and fold to shape. Silver solder the two pieces together. Cut the sandwich piece for the sight glass, mark and drill the holes for the retaining screws, 1.4 mm initially, place on the tank side and spot and drill through 1.4 mm. Tap the tank holes 10 BA and open out the holes in the sandwich piece 1.8 mm
2. The Control Valve.
The control valve is made in three parts. The valve spindle is 3/32" stainless steel, the body and valve seat is brass. Take a piece of 6.4 (1/4") brass, cut and face both ends to 50 mm long. Centre drill and drill 3/32" diameter for a depth of 38 mm. Reverse in the chuck, drill 1.8 mm (8 BA tapping size) for a depth of 12 mm until it breaks through into the 3/32" hole. Open out this hole to 5 mm dia. for a depth of 7 mm. Tap the smaller diameter hole 8 BA. Turn the other end down to 3/16" diameter for a distance of 5 mm and thread 3/16" by 40 tpi for the gland nut. Make a suitable gland nut from 1/4" hex bar.
The valve seat is made by turning a piece of bar until it just enters the 5 mm hole in the valve body. Part off at 20 mm length. Centre the end and drill 1 mm through the length of the bar. Open out this hole to 3 mm for a depth of 8 mm. The valve seat and valve body are soldered together and a side hole, 1.5 mm diameter drilled through into the chamber, near the bottom of the valve body.
Make the valve spindle from a 60 mm length of 3/32" stainless steel. Turn down one end to 2 mm diameter for a distance of 6 mm and form a cone at the end. Thread the full diameter 8 BA for 8 mm distance. At the top end of the spindle, turn down to 2 mm diameter for 3 mm. Face a piece of 3.2 mm bar and drill 2 mm diameter for 2 mm depth. Drill a cross hole 1.5 mm diameter and part off at 4 mm. The handle is made from 1.5 mm silver steel and the spindle, boss and handle soldered together.
Place a gland nut on the spindle, wrap some PTFE tape around the spindle and screw into the valve body until it closes against the seat. Try blowing through the valve with the spindle screwed down. If it leaks separate the body and seat and examine the seat. If there is any burring at the valve seat, clean it up. Also check the cone on the spindle. If you still cannot get a seal, you may have to make a new seat.
The valve body is soldered into the tank, making sure that there are no leaks of air around the joints at both top and bottom. The air pipe is a length of copper (or brass) pipe. Bevel both ends and solder into the tank. Make a bush from 12 mm brass with an internal thread of 1/4" by 40 tpi and solder into the tank. Make a plug for this from 12 mm brass bar. I find it helps to replace the plug if the screwed portion is extended about 5 mm and turned down to 5 mm diameter. Knurl the plug for easy removal and fit an 'O' ring. It then only needs to be screwed finger tight in order to effect a seal.
The fuel tank is secured in place on the footplate by two 12 BA screws inserted through the cab rear into the top valance. The sight glass is a piece of clear styrene sheet (40 thou') sealed with a coat of gasket cement round the cavity edges.
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If you have any questions, or comments or find any errors in these notes please contact me by email.
Email Keith Bucklitch.
Copyright © 1998, Keith Bucklitch
Last Edited - November 1998