Biscuit Tin Steam Engine. Part 8.

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Tony Bird

Senior Member
Feb 20, 2011
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Cardiff, South Wales, UK

Meanwhile back with the water feed pump. What follows is usually how I construct a water pump. The diameter of the ball seating is calculated by dividing the diameter of the ball by 1.40, which should seat the ball as shown in the drawing. (P.063).

063 BTE Ball and hole drawing. crop.jpg

Usually for this type of pump a ‘T’ shaped casting is used for the body. In this case, a shouldered sleeve which is threaded all the way though is glued into the original pump body. It was then cross drilled via the ram cylinder after which the cylinder was lapped. (P.064).

064 BTE Body sleaved.JPG

The centre part of the pump valve is threaded and drilled through at the ball seating size, one end being plain and the other is slotted to allow water to pass when the ball lifts. (P.065).

065 BTE Centre balll seating.JPG

The pump centre was screwed into the pump body until it had just covered the hole of the ram. Some glue was put onto the thread of the pump centre at the bottom of the ram cylinder; the pump centre was then screwed to its final position using a depth gauge. The pump centre was then drilled through its one side using the ram cylinder as a guide. The ram cylinder was then lapped again to get rid of any glue residue. (P.066).

066 BTE Ball seating screwed in.JPG

The pump was then fitted into a stand, it being secured by a grub screw on one side. (P.067).

067 BTE Pump on bracket.JPG

Making the pump unions and getting the clearance for the ball to lift when it is in use. The clearance for the ball is achieved by placing a ball on its seating in the pump and using a depth gauge to measure how far down it is. (P. 068).

068 BTE Measuring for shoulder.JPG

The two unions are made; and their threaded shoulder which goes into the pump is made the same length as the depth gauge is set. If the union didn’t have a hole in it, it would jam the ball solid in the pump but it having the hole allows enough movement of the ball to allow the valve to work. (P.069).

069BTE Pump top union.JPG

The water feed pipe which comes through the engine base plate fitted to the pump. (P.070).

070 BTE Bottom union and pipe.JPG

Another size of pipe bender is needed to create the swan neck for the boiler feed pipe from the pump; this bend allows the pipe to go back down through the base plate. (P071).

071 BTE Smaller pipe bending jig.JPG

The finished pump in place. Note, shouldered brass ferrules have been fitted where all the water and steam pipes go through the engine base plate. (P.072).

072 BTE Pump fitted.JPG

As all the allotted attachments have been used, a video of the pump in operation will be in the next episode. To be continued….
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