Abstract: A spiral piston ring made of self-lubricating material and having at least two complete convolutions and having a gradual and continuous taper except for the terminal portions thereof which taper at a steeper angle than the gradual and continuous taper, and with indentations in the convolutions adjacent to the terminal portions which are positioned and which have a size and shape to receive exactly the terminal portions.

Abstract: A compressor or pump or motor-type structure having a housing with a bank of cylinders and a shaft journalled for rotation therein and fitted with a swash plate, sometimes referred to in the art as a wobble plate or cam or drive, which is connected to pistons mounted for reciprocation in the cylinders and which will effect such reciprocation upon rotation of the shaft. When used as a motor, entry of fluid under pressure into the cylinder heads will effect displacement of the pistons and driving of the shaft. Improved means is provided in the present structure for supporting the swash plate against rotational forces imposed thereon, in the mounting of the swash plate and in the connection between the swash plate and the pistons.