Feed Pump

The feed pump is bolted on one side of the main pump cylinder block and works as a separate unit. The pump body (601) can most conveniently be made from a casting but it can also be fabricated from single parts and silver soldered together, or even machined completely from the solid. In any case some machining operations are necessary.

The rear surface should first be faced truly flat by holding the projecting part of the body in the 4-jaw chuck. Now the other drilling and tapping operations can be performed precisely to the rear surface reference. Care must be taken when making the seat for the valve ball (607). A special tool is recommended for this job. This tool, called a D-bit, can be easily produced from a piece of 5 mm silver steel, ground to about 60 degree on the front cutting face. A light blow with a brass rod onto the ball provides a perfect valve seat.

The pump plunger (602) can be made from 5 mm stainless steel and is sealed with an O-ring  5 x 1. Due to the lack of space the gland (603) cannot receive a hexagonal head. Instead, the head should have three holes drilled across in the head to permit tightening with a small bar such as a 1mm drill bit. The unions (608) and (609) are typical pipe connectors and are required several times in this machine. The nipple (609) is soldered on the pipe and then it is screwed with the nut (608) onto the discharge or inlet fittings.

The utility fittings

A number of small fittings remain to be made to complete the steam pump and its equipment. These may be described as ‘utility’ fittings, as they do not necessarily conform exactly to the design of those on the full-size engine.

The first parts in this group are the components for the most important boiler safety valve (701 to 705). This safety valve should be made really by experienced model engineers only as a failure of this component could result in a serious accident. Non-experts should rely on a bought-in product. In any case, a functional check, e.g. with compressed air, must be performed before using a boiler safety valve.

The parts (706) and (707) form a unit for the connection of the pressure gauge. A thin pipe Ø 3 mm is soldered in the ring flange (707) and bent to a siphon. The pressure gauge is fitted on the other end. However, this ring flange is required twice. It is also installed underneath safety valve, from where then the conduit to the blower valve (731) leads.

The plug (708) closes the blow-down (525) in the lower boiler skirt. The water level indicator or gauge glass is fabricated from individual parts silver soldered together. Whether it’s do-it-yourself construction, or a finished part from the specialized trade is preferred, every model engineer must answer for himself. All necessary information and dimensions to build it can be taken from the drawing. The same is valid on the double check feed valve. For normal operation one single valve is sufficient. However, if one wants to have  a hand pump in one of the rear side tanks, a double valve is needed.

The design of the main regulating valve and the blower valve are basically the same, differing only in their dimensions. All parts are made from brass, except for the valve spindles (722) (728) for which stainless steel is specified.

Conspicuous on the original machine are the thick suction tubes. For those we make the hose connector nipple (732), the union cap (734) and (735) and the strainer (736). The union cap (734) (735) is especially interesting. The part can be machined in one piece out from a Ø 20 mm brass rod. First step is to turn the projecting arms on both ends of the raw material. The arms should be longer in this stage than specified for the final part. This extension should be cylindrical for secure chucking for the following machining process.

In the second step the middle section can be finished with a ball turning apparatus in the lathe. Now, the arms can be made to final length and the ball can be clamped in the 4-jaw chuck. At this setting, the internal thread and the passageway drilling can be carried out. In the last setting the union cap should be screwed onto a mandrel to face the opposite side. The strainer (736) comprises three single parts, the connection part and the cap, both machined from brass. A rolled cylinder of perforated metal or gauze is fitted between them and soldered along the joint.

Making the suction hoses is another interesting job. Basic material for this is a grey, pressure resistant washing machine connection hose with an internal diameter of approximately 10 mm. These are cut to length with some over length and slide a Ø10 mm round steel bar inside. The hose should be clamped using hose clamps firmly to the steel bar. The hose is turned all over on low speed between centres in the lathe. Yes, it works really and a fine textured surface is the result. In the same setting a ‘thread’ is cut on the hose. A screw cutting feed of 5 mm is chosen. With a sharp lathe tool a fine groove will be scratched in the surface. Galvanized steel wire Ø 0.3 mm can now be wound in this groove. Finally the connection armatures are fastened and the tube protected with varnish. The result is a perfect looking fire brigade suction hose.

Similar parts are necessary for the delivery hoses. For practical purposes standard rubber or plastic tube can be used for this hose because they are not visible in the model. In the prototype they were kept in a separate box at the rear end of the superstructure and protected by a small door panel. This has not being realized in the model and is, therefore, not shown in the drawings. The delivery hoses are required only for demonstrating the machine. Therefore, you can use whatever you have at hand. The hose connectors (737) are thread to the admission of the branch pipe (920).

The air vessels (738) and (739) build up by using brass or copper tubes and end pieces, fabricated by silver soldering. The exact length and position of the steam and exhausted connections (740) and (741) should be determined on the pre-mounted model. There is not much room between the steam pump and the boiler; therefore both components have fairly short bends. The part (724) is an old friend and coming from the main regulating valve described previously in this chapter.

Some other conduits e.g. between the main tank and the feed pump and from there to the boiler feed check valve are not shown separately. These should be made from 4 mm dia. copper pipe with unions (608) (609) silver soldered to the ends. Again, the length and location must be determined on the pre-assembled model.

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