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A two-stage system for delivering fuel to a gas turbine including a first stage variable pump for serving as a primary source of fuel, a second stage fixed pump for selectively supplementing the variable pump, a bypass valve connected to the fixed pump for loading and unloading the fixed pump and a

A two-stage system for delivering fuel to a gas turbine including a first stage variable pump for serving as a primary source of fuel, a second stage fixed pump for selectively supplementing the variable pump, a bypass valve connected to the fixed pump for loading and unloading the fixed pump and a regulator valve assembly connected to the variable pump and the bypass valve for controlling operation of the variable pump and the bypass valve. Preferably, the two-stage system also includes a control valve connected to the regulator valve assembly for setting a pressure differential across the regulator valve assembly and, thereby, loading and unloading the fixed pump.

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What is claimed is: 1. A two-stage system for delivering fuel to a gas turbine comprising: a variable pump for serving as a primary source of fuel to an outlet of the two-stage system; a fixed pump connected to the outlet for selectively supplementing the variable pump; a bypass valve connected to

What is claimed is: 1. A two-stage system for delivering fuel to a gas turbine comprising: a variable pump for serving as a primary source of fuel to an outlet of the two-stage system; a fixed pump connected to the outlet for selectively supplementing the variable pump; a bypass valve connected to the fixed pump for loading and unloading the fixed pump as well as varying an incremental output of the fixed pump; and a regulator valve assembly connected to the variable pump and the bypass valve for controlling operation of the variable pump and the bypass valve, and, thereby, the fixed pump, wherein in a first mode of operation, only the variable pump provides fuel to meet demand, and in a second mode of operation, when the demand exceeds the fuel provided by the variable pump, the variable pump and the fixed pump provide fuel to meet demand. 2. A two-stage system as recited in claim 1, further comprising a control valve connected to the regulator valve assembly for setting a pressure differential across the regulator valve assembly and, thereby, loading and unloading the fixed pump. 3. A two-stage system as recited in claim 2, wherein the control valve is a jet pipe torque motor assembly controlled by an electronic engine controller. 4. A two-stage system as recited in claim 1, further comprising a check valve connected to an output of the fixed pump. 5. A two-stage system as recited in claim 4, wherein when the bypass valve closes, an output of the fixed pump creates a pressure build to open the check valve such that, the output of the fixed pump augments an output of the two-stage system. 6. A two-stage system as recited in claim 4, wherein the check valve opens at a pressure that is slightly higher than a discharge pressure of the variable pump. 7. A two-stage system as recited in claim 1, wherein the variable pump includes a pivoting cam ring to vary an output of the variable pump, a piston operatively connected to the cam ring to control the position of the cam ring and a cam actuator assembly to position the piston, wherein the cam actuator is operatively connected to the regulator valve assembly. 8. A two-stage system as recited in claim 7, wherein the cam actuator assembly is a half area servo. 9. A two-stage system as recited in claim 7, wherein the spool of the regulator valve assembly strokes to substantially redirect an output of the variable pump from the cam actuator assembly to the bypass valve to maximize the output of the variable pump and to close the bypass valve and, thereby, load the fixed pump. 10. A two-stage system as recited in claim 1, wherein the regulator valve assembly has a housing that defines three outlet ports and three inlet ports and a multi-part elongated spool slidably retained in the housing for selectively varying the flow through the outlet and inlet ports. 11. A two-stage system as recited in claim 1, wherein when the bypass valve is open, an output of the fixed pump passes through the bypass valve to mix with a low pressure area of the two-stage system. 12. A two-stage system as recited in claim 1, wherein when the bypass valve is closed, an output of the fixed pump passes is provided to the gas turbine. 13. A flow control system for a two-stage fuel pump comprising: (a) a regulator valve assembly in fluid communication with an output of fuel from a first stage, the regulator valve assembly including: i) a housing defining a plurality of ports; and ii) a spool slidably mounted in the housing for selectively blocking the ports; (b) a bypass valve operatively connected to the regulator valve assembly and a second stage for directing an output of the second stage; and (c) a control valve for varying a pressure differential across the regulator valve assembly to set a position of the spool and, thereby, control the bypass valve and the first stage such that the first stage is normally on and the second stage is selectively activated to supplement the output of the first stage, wherein the first stage is a variable displacement pump and a position of the spool determines an output of said first stage, and wherein the second stage is a fixed displacement pump. 14. A flow control system as recited in claim 13, wherein the control valve is a torque motor assembly including: (i) a flapper; (ii) a nozzle associated with the flapper and in fluid communication with the regulator valve and an output of the two-stage system such that a position of the flapper sets the position of the spool; and (iii)a coil assembly for setting a position of the flapper in response to a signal from an engine controller. 15. A flow control system as recited in claim 13, wherein the regulator valve assembly defines three inlet ports and three outlet ports. 16. A flow control system as recited in claim 13, wherein the regulator valve assembly defines four inlet ports and four outlet ports. 17. A regulator valve assembly for use in a pump system having a first stage and a second stage, the regulator valve assembly comprising: a housing defining first, second and third inlets and first, second and third outlets; and a multi-part elongated spool slidably retained in the housing for selectively varying the flow through the inlets and outlets; wherein when only a first stage is providing output, i) the first inlet is in fluid communication with the first outlet to create a spill return flow to vary an output of the first stage and ii) the second inlet is in fluid communication with the second outlet and the third inlet is in fluid communication with the third outlet to set an output of the second stage at zero, wherein when the first and second stage are providing output, i) the first outlet is blocked to maximize an output of the first stage and ii) the first inlet is in fluid communication with the second outlet and the second inlet is in fluid communication with the third outlet to bring the second stage online wherein the first stage is a variable displacement pump, and wherein the second stage is a fixed displacement pump. 18. The regulator valve assembly of claim 17, wherein the housing further defines a fourth inlet in fluid communication with an output of the second stage and a fourth outlet in fluid communication with the fourth inlet to form a spill return flow from the second stage output for providing fast response to varying engine demand when the second stage is online.