REGIONAL TECHNICIANS GROUP
Equipment Repair Guide (updated September 1999)
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Absolute Zero Demonstration Apparatus (or Constant Volume Gas Thermometer) The gauge can be removed and dismantled to clean any blockages or corrosion from the orifices using stiff wire or a fine hook. When using this piece of equipment, it is most essential that the highest temperature investigated does not exceed 100°C. The soft-solder, joining together the two halves of the ball, may begin to melt and cause the ball to 'explode' under the pressure thereby creating a hazard to the operator.
Triple
beam balances - A very common problem is missing zero-adjustment knobs
and locating springs. Replacements are available from Hollywood S.H.S.
(at cost) or a 3/16" gutter bolt and nut provides a good substitute.
If zero adjustment cannot be achieved by turning the adjusting knob, then
weights need to be added to, or removed from the balance pan. The weights
are accessed by screwing off the pan - only small adjustments are usually
necessary and lead shot is ideal for the purpose. If the aluminium damping
leaf rubs on the damping magnets, then the leaf itself may be bent (which
can be carefully straightened), or the beam may be out of alignment. This
can be re-aligned by adjusting the large hexagonal nut on the underside
of the balance. Damaged bearings (made from glass or agate) can be replaced
by first levering off the bearing covers either side of the balance - replacement
bearings are available from Hollywood S.H.S. Replacement scales can be
made by removing a good one from another balance, photocopying onto an
overhead transparency and mounting into position with a white paper backing.
Van
de Graaf generator - Preventive maintenance is highly recommended for
this piece of equipment. The generator should be stored covered and well
away from corrosive chemical fumes, when not in use. Build up of dust or
corrosion can cause electrostatic charges to leak into the atmosphere,
making the generator very inefficient. Performance may be greatly enhanced
by cleaning the acrylic tube, and by working up a high polish on the large
dome using metal polish. Various types of collector brushes are available,
from 'point conductors' (which can be substituted with copper gauze fixed
into place along one edge, and a few strands of copper removed from the
other edge to form the collectors), to an aluminium plate collector held
in position with spring clips. In all cases, the collector should not touch
the belt, as damage may occur to the belt. Replacement belts are available
from the manufacturer (most models are from IEC in Melbourne), but care
must be taken to measure the old belt as there are a number of different
lengths. Fitting the belt is made easier by first tying a string to the
belt and threading it through the tube to pull the belt through. If the
belt has a join, make sure that the join is to the outside so that it does
not bump over the rollers. Some newer models have a coated plastic discharge
sphere which is quite fragile. By keeping the generator clean and shiny,
and experimenting with different collectors, the performance of the generator
can be greatly enhanced.
Spirit
thermometer threads - these often separate leaving broken threads of
alcohol along the capillary of the thermometer. These can be rejoined by
immersing in a beaker of cooking oil heated on a hotplate to approximately
130deg.C. The thermometer should be observed carefully and removed when
the thread has joined up, or the alcohol has entered into the bulb at the
top end of the capillary tube. If the end bulb fills completely and heating
is continued, then the thermometer will break. The thermometer should not
be heated over an open flame as sudden high heat is more likely break it,
and the spirit is flammable.
Soldering
techniques - the selection of an appropriate soldering iron is most
important. For general electronic and repair work in the lab. a minimum
power rating of 25watts is essential. The tip of the soldering iron should
be kept clean and 'tinned' at all times - cleaning during soldering is
best done by wiping the tip of the iron on a damp sponge and immediately
after cleaning, solder should be applied to the tip to prevent it oxidizing.
If the iron is badly oxidised, it may need to be cleaned with emery cloth
or even filed (when cool) and then re-tinned as above. Resin cored solder
is preferred as it contains a resin, or flux, which helps prevent oxidation
and aids the flow and adhesion of the solder. The soldering iron should
be considered as means of transfering heat rather than a means of applying
solder, with the solder being applied to the heated joint. Always tin (apply
a small amount of solder to) the tip of the iron before heating the joint,
as the molten solder will transfer heat to the joint more efficiently (liquids
transfer heat better than solids.)
Both parts of the joint should be heated simultaineously by holding the iron stationary at the junction, then apply the solder to the heated joint. It is often easier to tin the parts separately before joining them together and a "third hand" is a very useful aid to hold parts to be joined. Commercial stands can be purchased to hold the work, leaving both hands free to manipulate the soldering iron and solder, or a very simple stand can be made from a piece of stiff wire inserted into a wooden base, and an alligator clip attached to the end of the wire.
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