Patent ID: 8529317

Claim:
A speed control device for a pneumatic power tool which includes a housing with a pressure air inlet, an output spindle, an air turbine with a turbine wheel drivingly connected to the output spindle, wherein a plurality of nozzles are arranged for directing motive air onto the turbine wheel, and wherein the speed control device includes a valve unit for controlling pressure air flow through the nozzles in response to a speed responsive parameter, wherein: said plurality of nozzles are divided into n separate nozzle groups having individual air feed through individual air feed passages, wherein n is an integer and n>1; the valve unit is capable of being actuated into n states for controlling air feed to said n nozzle groups, whereby for each subsequent state, x air feed passages are connected to the pressure air inlet such that nozzle groups 1 to x are fed with air, wherein x is an integer and 1≦x≦n, the valve unit includes a valve element which has a cylindrical skirt portion with one or more radial apertures which are arranged to co-operate with a number (n) of axially differently oriented radial openings in a valve housing, wherein the valve element is sealingly axially movable, and said radial openings are respectively connected to said air feed passages, and the one or more radial apertures are positioned to be evenly distributed around the circumferences of associated valve parts in order to obtain force balance in radial directions of said parts.