Abstract: Disclosed is a system for controlling the static pressure within a controlled space, the controlled space having a supply duct for providing air to the space and a return duct for exhausting air from the space. The system comprises apparatus for adjusting the amount of air being supplied to the controlled space. The system further comprises a minimum/maximum control having a single adjustment for controlling either the minimum flow rate or the maximum flow rate in both ducts simultaneously (a minimum/maximum control having a single adjustment for controlling the minimum flow rate in both ducts simultaneously and a single adjustment for controlling the maximum flow rate in both ducts simultaneously is also consistent with the present invention).

Abstract: A pneumatic apparatus or relay which, in one embodiment, maintains the output pressure at a fixed level until the signal pressure obtains a predetermined value at which time the output pressure varies according to the signal pressure and, in a second embodiment, maintains the output pressure at a first level, which may be essentially zero, until the signal pressure obtains a predetermined value at which time the output pressure assumes a second level until the signal pressure reaches a second predetermined value and then the output pressure varies according to the signal pressure.