Fail-safe servo-controlled mixing valve

Claim 1

A fail-safe servo-controlled mixing valve for mixing two fluids in accordance with a variable determined by the action of a sensing element including in combination: a. a casing structure 1 defining a first passageway 3 for a first fluid A a second passageway 4 for a second fluid B, a mixing chamber 5 for mixing said first fluid A and said second fluid B, a first orifice o1 between said first passageway 3 and said mixing chamber 5, a second orifice o2 between said second passageway 4 and said mixing chamber 5, and said casing structure further defining a third passageway 6 forming an outlet from said mixing chamber; b. a servo fluid motor 14 including a movable partition 14a, 14b, 14c, 15 arranged inside said casing structure 1 and separating said first passageway 3 from a servomotor cylinder chamber c adapted to be maintained at pressure levels different from the pressure prevailing in said first passageway 3, said partition 14a, 14b, 14c, 15 having a predetermined effective area exposed to the pressure of said first fluid A in said first passageway 3, c. spring means 17 in said servomotor cylinder chamber biasing said partition 14a, 14b, 14c, 15 in a direction opposite to the direction of the pressure of said first fluid A inside said first passageway 3 upon said partition 14a, 14b, 14c, 15; d. a main valve stem 9 having one end fixedly attached to said partition 14a, 14b, 14c, 15 and operable in a direction longitudinally thereof by said partition 14a, 14b, 4c, 15 and having another end remote from said partition 14a, 14b, 14c, 15, said main valve stem 9 being unsupported between said one end and said another end thereof; e. a first valve element 10 fixedly mounted on said main valve stem 9 controlling the flow of said first fluid A through said first orifice o1 into said mixing chamber 5 and being acted upon by the pressure of said first fluid A in said first passageway 3 in the same direction as the action of said spring means 17 upon said partition 14a, 14b, 14c, 15; f. a second valve element 11 fixedly mounted on said main valve stem 9 controlling the flow of said second fluid B through said second orifice o2 into said mixing chamber 5 and being acted upon by the pressure of saId second fluid B in said second passageway 4 in a direction opposite to the action of said spring means 17 upon said partition 14a, 14b, 14c, 15; g. balancing means 12 for said second vale element 11 fixedly mounted on said main valve stem 9 arranged in said second passageway 4 and acted upon by the pressure of said second fluid B in the same direction as the action of said spring means 17 upon said partition 14a, 14b, 14c, 15; h. means defining a first control duct 18, 23 communicating between said first passageway 3 and said servomotor cylinder chamber c, said first control duct-defining means 18, 23 having a first valve-element-controlled servo orifice p1 arranged between the ends thereof; i. means defining a second control duct 23, 20 communicating between said servomotor cylinder chamber c and said third passageway 6, said second control duct defining means 23, 20 having a second valve-element-controlled servo orifice p2 arranged between the ends thereof and in registry with said first servo orifice p1 and having a predetermined spacing from said first servo orifice p1; j. a sensing-element-controlled servo-valve stem 22 movable in a direction longitudinally thereof and arranged in registry with said first servo orifice p1 and said second servo orifice p2; and k. servo-valve element means 21 on said servo-valve stem 22 having a spacing different from said predetermined spacing between said first servo orifice p1 and said second servo orifice p2 for varying inversely the effective area of said first servo orifice p1 and said second servo orifice p2 for varying inversely the effective area of said first servo orifice p1 and of said second servo orifice p2 upon movement of said servo-valve stem 22 in a direction longitudinally thereof.