Abstract: A vacuum or pressure unit to be incorporated in a vacuum or pressure system of a vehicle which operates, or assists in the operation of, at least one vehicle component, the vacuum or pressure unit comprising a pump in fluid communication with the vacuum or pressure system of the vehicle, an electric motor operatively connected to the pump to drive the pump and connected to a source of electrical energy via a pressure responsive electric switch mounted in the vacuum or pressure system of the vehicle, the pressure responsive electric switch being intended to close the electrical circuit between the electric motor and the electrical energy source to activate the electric motor upon the magnitude of the pressure in the vacuum or pressure system being insufficient to operate or assist in the operation of the vehicle components at the desired efficiency.

Abstract: In a system for delivering air from an air pump to an exhaust system and accessories for an internal combustion engine, an air flow control unit has a high pressure relief valve, an outlet open to the exhaust system, a vent open to the atmosphere and an outlet open to the accessories with a check valve therein. A valve member is movable in response to an engine signal between a first position closing the exhaust system outlet and a second position closing the vent; and a low pressure relief valve is included in the vent to maintain a minimum low pressure in the unit when the valve member is in its first position.