The effect is to prevent the exchange of oil from any two adjacent chambers located on either side of a given sealing area and the oil can only be interchanged by the actual rotation of the rotor and vanes. This is the pumping mechanism for the historical vane pump or motor. The term 'pressure balanced' comes from the fact that pressure in any chamber is matched by the same pressure in the diametrically opposite chamber and the hydraulic radial side thrust calculated by a 'side view area' and the two forces are opposite and cancel; hence the name