Instrument calibrating demand flow regulator

Calibration system for calibrating an instrument, comprising:

• a source of calibration gas;
• a housing having an interior, said housing being provided with an inlet connected to the source of calibration gas, and an outlet for connection to the instrument to be calibrated;
• a movable element disposed within the interior of the housing and movable in response to a pressure differential on opposite sides of the movable element;
• a demand flow valve element disposed within the interior of the housing to form a first space within the interior between the movable element and the demand flow valve element;
• a pressure regulating valve device disposed within the interior of the housing to form a second space within the interior between the demand flow valve element and the pressure regulating valve device;
• said demand flow valve element being movable between one position in which gas flow between said first space and said second space is prevented and a second position in which gas flow between said first space and said second space is permitted, said demand flow valve element being operatively associated with said movable element so that movement of the movable element caused by a pressure differential across the movable element results in movement of the demand flow valve element from the first position to the second position, said pressure regulating valve device being movable between a first position in which the flow of calibration gas into the second space is prevented and a second position in which the flow of calibration gas into the second space is permitted, said pressure regulating valve device being movable from the first position to the second position in response to the pressure in the second space being reduced to a predetermined level after said demand flow valve has moved away from said first position.