Abstract: An air compressor includes a stator, which includes an inlet and an outlet and defines a substantially cylindrical bore, and a rotor eccentrically rotatably mounted in the bore. The rotor is connected to be rotated by a three-phase asynchronous electric motor of pole amplitude modulated type which is switchable between low speed six pole operation and high speed four pole operation under the control of a controller. A pressure sensor communicates with the compressor outlet and is connected to the controller which is arranged to produce a first signal when the compressor discharge pressure falls below a first threshold value and a second signal when this pressure rises above a second threshold value.

Abstract: A rotary positive displacement air compressor includes a stator containing a rotor and having an inlet and an outlet. The inlet includes two or more inlet apertures in parallel associated with independently actuable pistons. Detecting means detects the pressure of the compressed air and produces a signal when this pressure exceeds or is less than predetermined values and thus indicates whether the rate at which air is being compressed exceeds or is less than the compressed air demand to which the compressor is subjected. The two pistons are associated with respective actuating means which are controlled by the detecting means for opening and closing each inlet aperture independently to vary the rate of air flow through the inlet.

Abstract: A positive displacement rotary compressor includes a stator which contains a rotor and has a stator inlet communicating with atmosphere via a first pilot operated valve and a stator outlet connected to a primary lubricant reservoir via a non-return valve and to an auxiliary lubricant reservoir via a second pilot operated valve and one or more lubricant injection orifices arranged to inject oil into the stator and connected to the primary reservoir via a third pilot operated valve and to the secondary reservoir. The compressor also includes a pilot control system responsive, in use, to the compressed air load to which the compressor is subjected and arranged to switch the first and third pilot operated valves from an open position to a closed position and the second pilot operated valve from a closed position to an open position when the compressed air load falls below a predetermined value. The auxiliary lubricant reservoir is always at substantially atmospheric pressure.

Abstract: An air compressor wherein oil mist lubricates a rotor stator in the compressor casing whereby an oil mist is produced in the compressed air provided with primary and secondary oil removal sections. The primary and secondary oil removal sections are connected by an oil separation manifold. The manifold and the secondary oil removal section are in a housing detachable from the main compressor housing. The main and detachable housings communicate with a tube which has apertures in its side wall at its inlet end which end communicates with the interior of the main housing and apertures in its side wall at its outlet end which end communicates with the manifold.

Abstract: A rotary oil sealed compressor including an unloader valve to restrict or close the compressor intake when the compressor pressure rises above the normal working pressure (i.e. when the demand for compressed air drops or ceases) and a minimum pressure valve arranged to ensure that the pressure within the compressor never drops below a predetermined minimum value, further includes venting means responsive to the rise in pressure in the compressed air supply line above a predetermined value exceeding the normal working valve arranged to vent the delivery and compression spaces of the compressor. Thus under no-load conditions the pressure within the compressor is reduced to a relatively low level which considerably reduces the power consumed when the compressor is idling.