Abstract: A pilot mechanism for a pressure regulating valve having a relatively high pressure inlet, a relatively low pressure outlet and main valve pressure responsive means for operating the main valve to control the pressure of the fluid downstream of the main valve. The pilot mechanism comprises pilot valve means for supplying a loading fluid to one side of the main valve pressure responsive means. A normally closed bleed leakage path is provided in communication with the loading fluid supplied to the main valve pressure responsive means for directing loading fluid away from the main valve pressure responsive means when the bleed path is opened. Second pressure responsive means are provided responsive to the pressure of the fluid to be controlled for controlling the position of the pilot valve means to in turn control the flow of loading fluid supplied to the main valve pressure responsive means.

Abstract: An improved air horn is provided which includes a housing having an inlet for receiving a pressure medium to operate the horn and an outlet for the pressure medium. A first chamber is disposed between the inlet and outlet and receives the pressure medium from the inlet. A conventional sound-emitting horn is connected to the housing for receiving the pressure medium from the outlet, with the horn having a predetermined frequency. A closed resonating tube is connected to the other side of the housing, and a diaphragm is disposed between the first chamber and the resonating tube for oscillating movement in response to pressure changes in the first chamber and the resonating tube. A relatively small diaphragm having a natural frequency higher than the horn frequency is selected, as it is more economical and requires less energy to vibrate it.