9 THERMOSTATICALLY CONTROLLED VALVES, SIGHT GLASSES, ELECTROMECHANICAL SAFETY APPARATUS FOR PROTECTING AGAINST BOILING OVER OF HEATED LIQUIDS, ELECTROMECHANICAL APPARATUS FOR INDICATING LACK OF WATER IN HEATING AND STEAM BOILERS, (( FILTER COTROLS, LEAKAGE TESTERS, )) HYDRAULIC AND PNEUMATIC CONTROL AND ADJUSTMENT APPARATUS FOR FINAL CONTROL ELEMENTS, MECHANICALLY ACTUATED SELF-CLOSING CHECK VALVES, (( MECHANICAL APPARATUS FOR AUTOMATIC ACTUATION OF THE RAPID ACTION SHUT OFF VAVES ON BLOW DOWN AND TANK CAR VALVES, )) ELECTRICAL CONTROL DRIVES FOR ARMATURES, LEVEL CONTROLS, WATER LEVEL ELECTRODES, SWITCHING INTENSIFIERS, IMPULSE BREAKERS, PHOTOMETRIC OIL AND TURBIDITY DETECTOR FOR INDICATING OIL LEAKS INTO WATER AND ESPECIALLY CONDENSATE PIPES, TWO-STEP CONTROLLERS, ELECTRO-PNEUMATIC APPARATUS FOR THE AUTOMATIC CONTROL OF BLOW DOWN VALVES ON HEATING AND STEAM BOILERS, OPACIMETERS, (( FLOW QUANTITY METERS, TWILIGHT SWITCHES, )) TEMPERATURE CONTROLS, (( HEAT QUANTITY METERS, AND HYGROMETERS, )) HYDRAULICALLY, PNEUMATICALLY AND MECHANICALLY-ACTUATED RAPID ACTION SHUT OFF VALVES, RETURN-TEMPERATURE CONTROL VALVES, HYDRAULIC AND PNEUMATIC CONTROL DRIVES FOR ARMATURES