| 摘要 |
<p>A vacuum operated sewage system includes a static pressure sensor establishing a trigger signal at a selected first level in a standpipe. The sensor is connected upstream of a discharge control valve and actuates a trigger and timer controller at the selected sensed pressure to establish flow for a predetermined period. A separate air admission control is provided to separately actuate the timer controller if the vacuum level in the sewage flow line drops below a selected level, to thereby reset the system vacuum pressure. The air admission control includes a level trigger valve operable to actuate the controller. A by-pass pressure sensing valve has an input connected to sense line pressure and holds the trigger valve in standby until the line pressure drops below a selected vacuum pressure. A resettable fluid timer is also connected to the level trigger valve and is charged under normal pressure system conditions. The timer holds the trigger valve in the set state for a selected period after the by-pass sensing valve responds to system level pressure decreasing below the selected minimum operating pressure and thereby prevents response to momentary changes in the flow line vacuum level.</p> |
