Pneumatic controller and alarm for adsorbent fractionaters, particularly dessicant dryers

Claim 1

A controller for an adsorbent fractionater having two adsorbent beds which are alternately switched between an on stream condition in which a bed is processing the product stream and an off stream condition in which a bed is first regenerated and then repressurized prior to being switched to the on stream condition, the alternate switching of the beds being effected by a flow valve system comprising inlet valves for selectively admitting gas to be processed into the adsorbent beds and exhaust valves for selectively releasing regeneration gas from the beds, the flow valves being controlled by pneumatic pilot signals, the controller comprising: a source of pressurized gas; first control valve means for selectively supplying pilot signals from the source to the inlet flow valves; second control valve means for selectively supplying pilot signals from the source to the exhaust flow valves; a pressure regulator for selectively reducing the pressure of the source gas to a lower, regulated pressure; first and second pneumatic accumulators; third control valve means to control the first and second control valve means to generate a schedule of pilot signals at the pressure of the gas source, the third control valve means comprising first and second variable orifices, the schedule of pneumatic pilot signals being based on the time intervals required to raise the pressures in the pneumatic accumulators from respective starting pressure levels to within respective predetermined pressure differentials relative to said regulated pressure, the time intervals being selectively variable through independent adjustment of the orifice sizes and the regulated pressure output of the pressure regulator, the pressure level of the pilot signals being unaffected by variations in the output of said pressure regulator.