of the rod and the crank pin bearing boxes; (2) by adding or removing shims between piston and socket type wrist pin boxes; (3) by screwing in or backing out the wrist pin adapter, in compressors having a threaded wrist pin adapter; (4) by turn- ing the piston rod in or out of the cross head, in double-acting pistons equipped with piston rod and  cross  head.  In  some  compressors,  the  piston clearance is nonadjustable. Control  Devices Because   of   the   great   variety   of   control, regulating, and unloading devices used with com- pressors, detailed instructions on their adjustment and   maintenance   must   be   obtained   from manufacturers’ technical manuals. When  a  control  valve  fails  to  work  properly, disassembly and a thorough cleaning is usually necessary. Some control valves are fitted with filters filled with sponge or woolen yarn, to pre- vent dust and grit from being carried into the valve chamber and to remove gummy deposits which come  from  the  oil  used  in  the  compressor cylinders.  Replace  the  filter  element  with  the specified material each time a valve is cleaned. WARNING: DO NOT use cotton as a filter element because it will pack down and stop the air flow. Since relief valves are essential for the safe operation of a compressed air system, they must be kept in satisfactory working condition at all times. Relief valves should be set as specified by the manufacturer, and tested by hand each time the compressor is started. Periodically, the set- ting of relief valves should be checked by raising the pressure in the space which they serve. Lubricating and Cooling Systems The maintenance procedures for lubricating and cooling systems in air compressors are similar to the procedures used for lubricating and cool- ing  systems  in  internal  combustion  engines.  For air-cooled compressors, steps must be taken to keep the cooling fins clean. Oil and dust act as insulators and, if allowed to collect on the fins, will prevent heat transfer. In general, the lubricating system of a com- pressor will give you little trouble if the follow- ing steps are taken: 1. Keep the reservoir oil at the prescribed level in order to maintain proper oil temperature. 2. Change crankcase oil periodically, flush the crankcase, and clean the oil filter. 3. Maintain proper lube oil pressure by keep- ing  the  oil  pump  in  good  working  condition  and by adjusting the bypass relief valve. 4. Keep the oil cooler free from leaks to pre- vent oil contamination and emulsification. 5. Inspect cylinder lubricators. a. When Navy Symbol 9000 series oil is used for compressor cylinder lubrication, the sight flow indicators should be filled with glycerine alone. b. When Navy Symbol 2000 series oil is used for cylinder lubrication, the sight flow in- dicators should be filled with a mixture of 50% distilled water and 50% glycerine. 6. Keep the lubricator in proper adjustment for the specified quantity of oil feed. The   general   requirements   for   care   and maintenance of compressor cooling systems are as  follows: 1. Intercoolers and aftercoolers should be in- spected   periodically. 2.  Collections  of  gummy  oils  or  tarry substances on the sides of cooler tubes should be removed by washing the tube nests with a cutting solution. Be sure that the nests are completely dry before  reassembly. 3. Any leaks in tube nests must be repaired; otherwise, water will leak into the compressor while it is secured, and air will leak into the water side during operation. If during operation, a water relief valve on the coolers blows while the cooling water pressure is normal, it is evident that a tube in the cooler is ruptured.  The  compressor  should  be  secured  im- mediately and the tube plugged, if possible. 4. Cylinder water jackets should be inspected and  cleaned  periodically  with  a  cleaning  nozzle. ENGINEMAN  1  &  C 7-4