GENERAL OVERHAULING Machines should be given a complete overhauling and thorough clean- ing at least once a year or oftener if conditions warrant, Smaller machines, whose windings are not sufficiently accessible, should be taken apart for cleaning. Loose dust and dirt can be removed by suction or compressed air as outlined previously. Heavy dirt and grease may be removed by cloths, brushes, or scrapers, using caution not to damage vulnerable parts of the machine. Carbon tetrachloride is the most efficient and the safest cleaning agent for the removal of grease, oil, and sticky dirt. It is non- inflammable, but sufficient ventilation should be provided to avoid toxic effects. Inflammable liquids such as gasoline are not recommended because of the fire and explosion hazard involved. The most effective method of applying the cleaning liquid is to spray it on with an atomizer. The pressure may be about 80 lb. for insulation in good condition, but should be no more than about 40 lb. for old insulation. If an atomizer is not available the liquid may be applied by a cloth or paint brush, a brush being handier for getting into corners and between small coils. Regardless of the method of application, care should be taken not to soak the insulation with the cleaning liquid. While the cleaning methods described permit the insulation to dry quickly at ordinary room temperatures, it is advisable to make certain that all moisture has been driven off by heating it as previously discussed under "Drying of Windings" especially if varnish is to be applied. 3-54