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.
With the lamps using petrol, the only parts requiring attention are the
plate from which gas issues and the wick. Unlike the paraffin nipple,
this is a circular stamping of brass approximately 3/4 in. in diameter
with a fine hole in the centre. To remove this disc, pass a long flat
screwdriver blade through two openings in the nozzle and turn to the
left (anti-clockwise), holding the body of the lamp firmly on the bench.
Before fitting a new disc, thoroughly clean recess and remove any
deposit from the inside of the valve box. Unscrew the needle and gland
if there is any leak there, and clean and repack with asbestos yarn. A
little glycerine on the packing appears to be an advantage. Place the
disc in position, dip an asbestos washer in water, and screw the nozzle
firmly down.
The wick inside the lamp filters the spirit before reaching the nipple
and occasionally needs replacing. Remove the cap from the bottom of the
lamp, and with a piece of thick wire flattened at one end and filed to a
hook, push it up the tube and withdraw the old wick. The new one is
simply put in its place and the cap screwed tight. The washer under the
filled cap is of cork and rarely gives any trouble.