Importance

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Abstract

A vacuum dual control system for the flat box section of a papermaking machine. The system includes a plurality of serially arranged vacuum boxes and a header interconnecting the boxes. A vacuum pump is operatively connected to the boxes in a manner so that vacuum applied to the boxes is a function of the speed of the pump. A first control operates the pump to run at an initial substantially constant high speed for providing vacuum necessary to dewater a web in its initial condition. The web is passed over the boxes so that suction applied therethrough by the pump running at its initial substantially constant high speed dewaters the web until the condition of the web changes sufficiently to cause the vacuum in the last box to increase to a predetermined maximum level. A second control is provided with set point adjustment capabilities to enable selection of a predetermined set point corresponding to the predetermined maximum vacuum level. The second control is connected to the last box and the vacuum pump and includes a sensor to sense the vacuum as determined by the second control sense point and only operable in place of the first control. Operation of the first control is terminated the control is initiated in response to the sensor sensing the vacuum level reaching the maximum level as determined by the second control set point to correspondingly lower the speed of the vacuum pump and maintain the maximum vacuum level.

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First Claim