Abstract: A vacuum pump includes two pairs of piston and cylinder assemblies mounted on opposite sides of a crankshaft in a common plane with the gas inlets for the first and second cylinders of a first pair of piston and cylinder assemblies being connected to the device to be evacuated and the gas outlets thereof being connected to a common outlet having a spring biased one-way valve controlling the outlet and to a passage connected to the inlet of a third cylinder in said second pair of piston and cylinder assemblies. The gas outlet of the third cylinder is connected to the inlet of the fourth cylinder and the gas outlet of the fourth cylinder is connected to the common outlet through spring biased one-way valves.

Abstract: A reciprocatory piston and cylinder machine particularly suitable for use as a vacuum pump includes a cylinder (17), a cylindrical piston (16) relatively slidably reciprocable within the cylinder (17), and means for substantially sealing the annular space between the piston (16) and cylinder (17) in lieu of oil or other liquid lubricant. The sealing means comprises a sleeve (102) of a low-friction material disposed under circumferential tension, and preferably also under longitudinal tension, on the cylindrical surface of the piston (16). Also disclosed is a reciprocatory piston and cylinder machine of particular prior construction having a one-way valve (42) in an exhaust port (30) ahead of a head portion (24) of the piston (16). The arrangement is such that, as the front face of the piston head portion (24) approaches the closed cylinder end (52), the piston head portion 24 physically moves the one-way valve (42) so as to open the exhaust port (30).

Abstract: A reciprocatory piston and cylinder machine particularly suitable for use as a vacuum pump includes a cylinder (17), a cylindrical piston (16) relatively slidably reciprocable within the cylinder (17), and means for substantially sealing the annular space between the piston (16) and cylinder (17) in lieu of oil or other liquid lubricant. The sealing means comprises a sleeve (102) of a low-friction material disposed under circumferential tension, and preferably also under longitudinal tension, on the cylindrical surface of the piston (16). Also disclosed is a reciprocatory differential piston and cylinder machine of particular prior construction having a one-way valve (42) in an exhaust port (30) ahead of a head portion (24) of the piston (16). The arrangement is such that, as the front face (28) of the piston head portion (24) approaches the cylinder end face (52), the front face (28) physically moves the one-way valve (42) so as to open the exhaust port (30).

Abstract: A porting and ducting arrangement for a pair of adjacent hollow cylinders includes respective pluralities of passages extending longitudinally in the walls of the cylinders. Each passage is provided with a port in communication with the interior of the associated cylinder. Plural recesses in the end of the cylinders or in a cover are each in communication with a separate passage or group of passages when the cover is applied to the cylinders. There are a pair of such recesses thereby associated with each cylinder and at least one recess of each pair is in communication with a recess of the other pair via duct means in the cover. Gasket means is retained between the cylinders and the cover to seal each recess of each pair of recesses with respect to the other recess of the pair.