How does a pneumatic system work on an aircraft piston engine?

The piston engine is the power plant. It generates thrust by turning the propeller, electrical power through the generator, hydraulic power with engine oil and/or a hydraulic system. It also sometimes has a vacuum pump in the form of a sliding vane pump to operate the mechanical gyros instruments. On a piston engine there is no "bleed air" supply. For the cabin pressure pneumatic system, piston aircraft, take compressed air from the compressor side of the turbocharger (or supercharger old airplanes) and routed into the cabin as long as the engine is running. The outflow valve which regulates how much air is let out of the cabin is used to maintain the desired cabin pressure. The cabin outflow valve is controlled by a cabin pressure controller where the pilot sets the cabin pressure and climb or descent rates. This is the only pneumatic system I can think of other than "de-icing boots" on the wing leading edge that are pneumatically operated.
A "receiver" is usually associated with a receiver/dryer in an air conditioning system.