—A large and efficient blowpipe that can be made in a few minutes is shown by [Fig. 69], the only materials required being a T-coupling and diminishing socket, an elbow, and one or two pieces of pipe. The air tube A (represented for the most part by dotted lines) passes through the diminishing socket until it almost reaches the nozzle of the blowpipe, with which it is concentric. By using the elbow D, the two supply pipes are brought parallel to each other, so that the indiarubber connecting tubes can be more easily held in the hand like reins, as by simply squeezing them the flame can be readily regulated. Sometimes, in cases of emergency, a plug drilled to meet the air tube is used in place of the socket. The plug is thrust into the end of the T-socket; but in all cases it must be airtight. This blowpipe can be used efficiently only in conjunction with a foot blower.
CHAPTER XIII
Managing Blow-lamps
The stoves and lamps burning paraffin in the form of vapour have become very popular on account of their good heating properties, portability, and little attention required. They consist of a container holding paraffin, a burner with a heating tube attached is screwed to the container, and a tube leading almost to the bottom. A small air-tube, similar to a cycle-pump, is fixed in container, the handle and cap only being in sight. When the burner tubes are heated, a thumbscrew on the filler caps is closed, and a few strokes of the pump puts a slight pressure on the oil in the container. The oil is forced up the central tube to the burner; but before reaching this it has to flow round the heating coils, and in so doing is turned to vapour. The outlet at the nipple being very small, causes the vapour to issue with some force, and it mixes with the air, forming a mixture which burns with a non-luminous flame similar to that of a bunsen burner. This flame plays on the heating coils, and once started, the lamp is practically automatic; a stroke or two from the pump will keep it going until the oil is consumed.
There are patterns that use petrol or benzol, their action being slightly different. Petrol and benzol are light spirits, which give off inflammable vapour at a much lower heat than paraffin does. Advantage is taken of this fact by causing burner and nipple to be in one solid brass casting, so that when the nozzle is heated, the brass conducts the heat back to the nipple and so vaporises the petrol, which is fed to the nipple by a thick wick contained in a tube which reaches almost to the bottom of the container, the wick touching the bottom.
To start either paraffin or petrol lamps, the exit tube or nozzle is heated. The petrol lamp has no coils round the nozzle; but comes straight from the holder to the exit nipple. The size of flame is regulated by a needle valve fitted with a wood or fibre handle. The petrol lamp has no pump, except on high-power brazing lamps whose use requires expert handling.
The chief trouble with lamps using paraffin is that the burner becomes choked; this is shown by the lamp jumping out or the flame not attaining sufficient heat. The makers supply a proper cleaning needle, a sheet stamped to form a handle and a piece of fine steel wire fixed at one end. Nothing else, such as pins, etc., should be used, or the hole in the nipple becomes enlarged, and emitting too much gas, causes a smoky flame. The cleaner should be used each time before lighting. A good way to avoid this trouble is to use a small funnel with fine brass gauze soldered in the body when filling. White Rose is a quite satisfactory oil for these lamps.
After considerable use the heating coil becomes choked with carbon deposit. A new heater tube can be obtained, or the old one cleaned by drilling two or three holes in the ends and passing a piece of flexible wire (such as Bowden brake wire) through the heater and removing the obstruction. After getting it clean, tap out the holes and fix suitable screws, flat under the head, with a piece of asbestos to make a tight joint.
If a larger flame is not obtained by pumping, take the cap off the pump and draw out the plunger; the leather is probably worn. Fit a new one; or it may have become hard, in which case apply a little oil and open out carefully. The retaining valve is in the centre of the pump bottom, and is removed by using a long key down the pump barrel. The valve is in four pieces. See that the spring is free and that the cork is in good condition. When replacing, take care not to get it cross thread, and screw firmly home. The washer under the filler cap is of rubber and cuts through in time. Do not use pliers to screw down; it will go gas-tight with the fingers if the washer is good.
To remove the nipple from which the gas issues is almost impossible without a proper key. This has a universal joint, which allows it to be rotated, although the handle is almost at right angles with the burner. Keys and all other parts mentioned can be obtained from any dealer in these lamps.