Abstract: A compressed air control system has a plurality of air-conducting airways connected between upstream and downstream headers. A control valve arrangement utilizes a main analog flow control valve in one of the parallel airways and at least one digital trim valve in another of the parallel airways. The control and trim valves respond to pressure changes in the downstream header and ensure that the control valve never closes more than 25 percent and never opens beyond 75 percent so as to stabilize system pressure.

Abstract: Apparatus for measuring or detecting one or more parameters of a gas, such as compressed air, in a line through which the gas is flowing by a sensing portion of an elongated wand which is axially inserted through piping attached to the line and advanced into the line radially thereof. The apparatus of the present invention, and the method of its use, avoid the problem of the wand being forcibly ejected from the piping upon removal thereof by providing an element having a diameter larger than the passageway in the packing gland through which the wand is inserted. The element is attached to an elongated tubing portion of the wand after insertion of the distal end of the tubing through the packing gland. The element may be one end of the probe containing the sensing elements, a plug closing the distal end of the tubing, or an additional, larger diameter of the section of tubing.