| 摘要 |
A vacuum limiting arrangement uses a three-port, two-position valve in conjunction with a vacuum sustaining valve to limit the vacuum applied to a vacuum driven device. A source of vacuum, such as engine intake manifold vacuum, is connected to one of two end ports. The device is connected to a central port, and the other end port is vented. The device can thus be connected either to the vacuum source in one position of the control valve or to vent. A control port that is effective to switch the control valve is connected into a vacuum line between the control valve and the device. The sustaining valve allows free flow of air from the device to the control valve, but only a restricted flow in the opposite direction to provide a hysterises to the system for controlling the shifting of the control valve, which is accomplished automatically as a function of the vacuum level at the device and in the control port. |
