discharged to atmosphere through a noise silencing muffler the temperature of the air can be maintained at a significantly warmer level by the use of a pressure control device in the exhaust system which will maintain the pressure inside the compressed air chamber the pressure which must be maintained to avoid icing can vary with the operating conditions but would typically be in the range of approximately 2 to 20 psig to accomplish this according to the present invention a typical air motor as shown schematically in fig1 may be adapted as follows the air motor generally designated by the reference numeral 1 may be of the piston diaphragm or rotary type having the volume of a working chamber 3 controlled by a piston diaphragm or vane type or the like device 2 wherein work is extracted from a pressure fluid such as air supplied at an inlet 4 spent pressure or partially spent pressure fluid is typically exhausted through a discharge orifice 5 to an exhaust chamber 7 or a muffler 9 or combination thereof to atmosphere at an outlet 10 due to varying inlet conditions of temperature and or water content within the pressure fluid and the inherent restrictions in the discharge through the exhaust chamber 7 and the end or the muffler 9 the exhaust air may be considerably expanded thereby.