Patent ID: 6935363

Claim:
A pressure control system for controlling the pressure of a process fluid stream at a certain location, the pressure control system comprising: a. a pressure regulator mounted downstream of an upstream process fluid line, the regulator having a closure member movable between open and closed positions for controlling process fluid flow through the fluid line, and a control chamber for housing an actuator fluid for acting on the, closure matter, wherein the position of the closure member changes in repsonse to changes in the pressure of the actuator fluid housed in the control chamber; b. an inspirator having an inlet, an outlet, and a throat between the inlet and outlet, the control chamber of the regulator being in flow communication with the throat of the inspirator; c. a primary pilot valve, including a sense port for receiving a sensed fluid pressure of the process fluid stream, a first target port for inputting a first target pressure, an inlet port for the actuator fluid in fluid communication with the outlet of the inspirator, an outlet port, and a primary valve member controlling the flow of actuator fluid between the inlet and outlet ports thereof and exiting the outlet of the inspirator, a first target pressure chamber in fluid communication with the target port and a sensed pressure chamber in fluid communication with the sense port, and a mechanism configured to move the primary valve member in response to a pressure differential between the target and sensed pressure chambers, wherein the sensed pressure chamber is in fluid communication with a sensing point along the process fluid line at which the pressure of the process fluid is to be controlled; d. a secondary pilot valve, including an inlet port connectible to a supply of the actuator fluid, an outlet port, a sense port connected to the outlet port, and a second target port for inputting a second target pressure, secondary valve member mounted for controlling the supply of actuator fluid to the inspirator inlet by controlling the flow of the actuator fluid between the inlet and the outlet ports thereof a target pressure chamber and a sensed pressure chamber, in fluid communication with the second target port and the outlet port thereof, and a mechanism configured to move the secondary valve member in response to a pressure differential between the target and sensed pressure chambers; and e. a target pressure source in fluid communication with the target ports and the target pressure chambers of the primary pilot valve and the secondary pilot valve and adjustable to select a desired pressure to be maintained at the sensing point in the process fluid stream.