PNEUMATIC CONTROL SYSTEM AND PNEUMATIC CONTROL DEVICE FOR SUCH A SYSTEM OR THE LIKE

摘要

A pneumatic control system having a source of control fluid providing two different control pressure levels for respectively switching the control device of the system from one operating condition thereof to another operating condition thereof, the control device comprising a pair of condition controller means each having a sensor and a bleed-type pneumatic valve operated thereby together with relay means operatively interconnected to the source for directing a branch signal of the control fluid to a pneumatically operated device in relation to a pilot signal directed to a pilot chamber of the relay means by one of the control means. First and second passage means are adapted to respectively interconnect the source to the valves of the control means, a pressure responsive means being disposed in the first passage means for preventing fluid communication therethrough when the source is at one pressure level and permitting fluid communication therethrough when the source is at its other pressure level. A switching means is provided in a third passage means and has one position for interconnecting only the second passage means to the pilot chamber whereby the pilot signal for the relay means is provided only by one of the controller means and having another position for interconnecting only the first passage means to the pilot chamber whereby the pilot signal or relay means is provided only by the other controller means.