Abstract: A secondary piston compressor has a crankcase, which is provided with a venting device. The latter includes an oil filter, which is constructed in the form of a superfine filter and is arranged in a separate housing. The superfine filter is in communication on the inlet side with an oil filler pipe of the crankcase via a conduit. It is connected on the outlet side to the atmosphere via an active carbon filter. On the inlet side, the superfine filter defines an oil collecting space, which is connected via a conduit to the crankcase with the interposition of a non-return valve. The non-return valve is held in its closed position by the pressure in the crankcase. When the secondary compressor is switched off, it opens and empties the oil collecting space of the superfine filter into the crankcase.

Abstract: Air is compressed in an air compressor and cooled in an air cooler whereafter the impurities which have condensed out are removed. The air is subsequently reheated in a heat exchanger which is connected on the hot air side between the air compressor and the air cooler. The reheated air is passed through a plurality of membrane-type nitrogen separators, whereby the permeate of the last separator is constituted by nitrogen of the desired purity. The concentrate of this separator is recirculated to the suction side of the air compressor. The output control of the apparatus can be effected by means of an air feedback line which branches off before the heat exchanger and leads to the suction side of the air compressor. The flow through the air feedback line can be controlled by a valve which operates in dependence on the outlet pressure of the air compressor.

Abstract: The apparatus includes an air compressor (13), which is cooled by direct oil injection, and an air cooler (14) connected downstream of it which serves as a condensate separator. Connected to it is a heat exchanger (18) which is heated by the waste heat from the oil discharged from the air compressor (13). The temperature of the air is raised thereby to a level at which the separators (4) downstream thereof develop their optimum efficiency. The nitrogen flowing out of the separators (4), the purity of which is predetermined by a downstream throttle (3), flows into an inflatable reservoir (5) which is connected to the suction side of a high pressure compressor. The latter discharges into a high pressure storage container which for its part supplies an injection moulding machine. The nitrogen is conveyed in a closed circuit between the injection moulding machine and the inflatable reservoir.