The invention is concerned with a piston compressor for the oilfree compression of a gas, especially oxygen, having at least one piston which is supported to be freefloating and is connected via a piston rod to a crosshead, the piston rod sliding in a guide bearing next the crosshead and in a gland next the cylinder.
In the case of such compressors in which the guide bearing is usually provided with oil scraper rings, the formation of a thin film of oil on the piston rod cannot be avoided on that portion of the piston rod which slides through the guide bearing. In the case of deficient functioning of the oil scraper rings, e.g., because of their having slowly worn away, this oil film can start to travel up the piston rod and thus push forward in the direction of the gland, which must be prevented especially when the piston compressor is serving for the comrpession of oxygen. In order to impede an advance of oil in the direction of the gland it has been usual hitherto to arrange on the piston rod a rubber ring which by means of a tubular spring is pressed against the piston rod which furthermore exhibits a recess into which the inner face of the rubber ring is embedded. The rubber ring indeed halts the advance of the oil film up the piston rod but itself becomes wet on the surface and can thus become a flinger ring for oil droplets which form on the ring itself. Oil droplets may also be flung off directly from the turns of the tubular spring because the tubular spring projects beyond the circumferential area of the rubber ring. Thus oil droplets flung off from the rubber ring and/or from the tubular spring may equally well arrive in the region of the gland.