Patent ID: 8393156

Claim:
A variable performance valve for use in a fuel nozzle for a turbine engine, the fuel nozzle including a housing having a fuel inlet and an outlet having a tip restriction therein, the variable performance valve being positioned between the inlet and the tip restriction, comprising: an outer sleeve held in fixed relation to the housing, the outer sleeve including an annulus formed in an inner surface thereof, an inner spool slidably positioned in relation to the outer sleeve, the inner spool including a first port positioned not to be in communication with the annulus in a no flow state of the nozzle and to come into communication with the annulus as the inner spool is slidably repositioned relative to the outer sleeve, the inner spool further including a second port in communication with the annulus and a fuel manifold of the inner spool, the inner spool further including an orifice providing fluid communication between the fuel manifold and the outlet tip restriction, and a spring positioned to provide a bias force to position the inner spool to the no flow state whereby the first port is not in fluid communication with the annulus; and wherein the first port and the orifice are sized relative to one another such that at low flow conditions a pressure drop from the inlet to the tip restriction is approximately equal to a pressure drop across the first port, at intermediate flow conditions the pressure drop from the inlet to the tip restriction is a sum of the pressure drop across the first port and a pressure drop across the orifice, and at high flow conditions the pressure drop from the inlet to the tip restriction is approximately equal to the pressure drop across the orifice.