Embedding knots and links in an open book III. On the braid index of satellite links

A pneumatically operated system for controlling the supply of water and/or water and air simultaneously to an air turbine-type dental handpiece, either to only drive the handpiece or drive it and simultaneously provide a spray. Two foot-actuated valves respectively controlling the supply of air to a handpiece are connected to a source of air under pressure and are respectively connected to a compound servo-control valve including a spool operable in a housing between various inlet and outlet ports for air which, when one foot-actuated valve is opened, will cause the spool to move from an initially inoperative position to afford delivery of drive air only to the handpiece and when the second foot-actuated valve is opened, additional air is by-passed at the same spool setting from one part of the housing to another part containing a normally closed water valve connected to water under pressure and opened by said additional air which actuates a small piston that engages said water valve to open it. The handpiece is supported in a holder by which the spool is maintained in said inoperative position. Springs restore the spool and small piston to their initial inoperative positions.