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A valve comprises a valve body and a shutoff assembly. The valve body includes an inlet, an outlet, and a fluid flow passage therebetween. The shutoff assembly includes a poppet and a piston. The poppet is movable between a closed position, a partially open position, and a full open position. The pi

A valve comprises a valve body and a shutoff assembly. The valve body includes an inlet, an outlet, and a fluid flow passage therebetween. The shutoff assembly includes a poppet and a piston. The poppet is movable between a closed position, a partially open position, and a full open position. The piston is disposed in the valve body adjacent to the poppet, and is moveable between a first position, in which the piston at least inhibits movement of the poppet from the closed position to the full open position, and a second position, in which the piston allows movement of the poppet from the closed position to the full open position.

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What is claimed is: 1. A valve comprising: a valve body including an inlet, an outlet, and a fluid flow passage therebetween; a poppet disposed in the valve body and movable between at least: a closed position, in which fluid is at least substantially restricted from flowing through the fluid flow

What is claimed is: 1. A valve comprising: a valve body including an inlet, an outlet, and a fluid flow passage therebetween; a poppet disposed in the valve body and movable between at least: a closed position, in which fluid is at least substantially restricted from flowing through the fluid flow passage; a partially open position, in which fluid is allowed to flow through the fluid flow passage at a first flow rate; and a full open position, in which fluid is allowed to flow through the fluid flow passage at a second flow rate that is greater than the first flow rate; a piston disposed in the valve body adjacent to the poppet, the piston moveable between a first position, in which the piston at least inhibits movement of the poppet from the closed position to the full open position, and a second position, in which the piston allows movement of the poppet from the closed position to the full open position; a poppet spring disposed adjacent to the poppet, the poppet spring configured to exert a poppet spring force against the poppet toward the closed position; and a piston spring disposed adjacent to the piston, the piston spring configured to exert a piston spring force against the piston toward the first position. 2. The valve of claim 1, further comprising: a poppet seat disposed in the valve body and configured to seat the poppet when the poppet approaches the closed position. 3. The valve of claim 1, further comprising: a piston stop coupled to the piston and configured to stop the piston when the piston has reached the first position. 4. The valve of claim 1, wherein the valve body further includes a pneumatic pressure sense port configured to receive a pressure sensor for sensing fluid pressure downstream of the poppet. 5. The valve of claim 1, further comprising: a chamber formed between the valve body and the poppet, the chamber configured to receive pressurized fluid. 6. The valve of claim 5, further comprising: a second chamber formed between the valve body and the piston, the second chamber configured to receive pressurized fluid. 7. The valve of claim 6, further comprising: a plurality of seals disposed proximate the piston and the poppet, the plurality of seals configured to at least restrict inadvertent fluid leakage into, out of, or between the first or second chambers. 8. The valve of claim 6, further comprising: a first pressurized fluid source configured to supply pressurized fluid to the first chamber; and a second pressurized fluid source configured to supply pressurized fluid to the second chamber. 9. The valve of claim 8, wherein: at least the first pressurized fluid source or the second pressurized fluid source includes a control valve. 10. The valve of claim 8, wherein: at least the first pressurized fluid source or the second pressurized fluid source includes a thermostat. 11. The valve of claim 1, further comprising: a guide disposed in the valve body and configured to guide the piston and the poppet. 12. A shutoff assembly for a valve having a valve body including an inlet, an outlet, and a fluid flow passage therebetween, the shutoff assembly comprising: a main body; a poppet disposed in the main body and movable between at least: a closed position, in which fluid is at least substantially restricted from flowing through the fluid flow passage; a partially open position, in which fluid is allowed to flow through the fluid flow passage at a first flow rate; a full open position, in which fluid is allowed to flow through the fluid flow passage at a second flow rate that is greater than the first flow rate; a piston disposed in the main body adjacent to the poppet, the piston moveable between a first position, in which the piston at least inhibits movement of the poppet from the closed position to the full open position, and a second position, in which the piston allows movement of the poppet from the closed position to the full open position; a poppet spring disposed adjacent to the poppet, the poppet spring configured to exert a poppet spring force against the poppet toward the closed position; and a piston spring disposed adjacent to the piston, the piston spring configured to exert a piston spring force against the piston toward the first position. 13. The shutoff assembly of claim 12, further comprising: a piston stop coupled to the piston and configured to stop the piston when the piston has reached the first position. 14. A valve comprising: a valve body including an inlet, an outlet, and a fluid flow passage therebetween; a poppet disposed in the valve body and movable between at least: a closed position, in which fluid is at least substantially restricted from flowing through the fluid flow passage; a partially open position, in which fluid is allowed to flow through the fluid flow passage at a first flow rate; and a full open position, in which fluid is allowed to flow through the fluid flow passage at a second flow rate that is greater than the first flow rate; a piston disposed in the valve body adjacent to the poppet, the piston moveable between a first position, in which the piston at least inhibits movement of the poppet from the closed position to the full open position, and a second position, in which the piston allows movement of the poppet from the closed position to the full open position; a first chamber formed between the valve body and the poppet, the first chamber configured to receive pressurized fluid; a second chamber formed between the valve body and the piston, the second chamber configured to receive pressurized fluid; a poppet spring disposed adjacent to the poppet, the poppet spring configured to exert a poppet spring force against the poppet toward the closed position; a piston spring disposed adjacent to the piston, the piston spring configured to exert a piston spring force against the piston toward the first position; and a piston stop coupled to the piston and configured to stop the piston when the piston has reached the first position. 15. The valve of claim 14, further comprising: a first pressurized fluid source configured to supply pressurized fluid to the first chamber; and a second pressurized fluid source configured to supply pressurized fluid to the second chamber. 16. The valve of claim 15, wherein: the first pressurized fluid source includes at least a control valve. 17. The valve of claim 16, wherein: the second pressurized fluid source includes at least a thermostat.