Importance

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Abstract

A liquid injection arrangement for inserting a foaming agent into water for a fire fighting application, or a similar use, requires that metered quantities of a liquid chemical foamant or other agent be injected into a conduit assembly conveying a water stream. A desired concentration of foamant requires varying the foamant flow as a function of water flow. A tank holds a quantity of liquid chemical foamant, and at least one pump has an inlet port coupled to the tank and an outlet port coupled to the conduit assembly. A hydraulic motor drives the pump and a valve is coupled with the hydraulic motor and a source of pressurized hydraulic fluid. A sensor is placed adjacent to the outlet port of the pump to feed back a signal representing the pressure of the water flowing through the conduit assembly, and a control system is responsive to the signal and to a flow rate of water flowing through the conduit assembly, producing a signal for controlling a speed at which the hydraulic motor drives the foamant pump. A feed-back loop is provided that monitors the flow rate and pressure of the water in order to control the foamant flow. The foamant outlet and the water/foam outlet pressure sensor are placed at substantially the same position in the flow so that the foam addition can be controlled to produce an accurately metered quantity of the liquid foamant in the water stream exiting the conduit assembly and to maintain the desired concentration.

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First Claim