| 摘要 |
<p>In systems using a main pump and a reserve pump where it is essential that pressure feed to a consumer unit, e.g., a vehicle booster steering device, be available in the event of failure of the main pump, the invention provides quick shifting to a reserve pump. The effect is achieved in two embodiments of the invention by means of a valve which is spring biased to a closed flow condition of the main stream from a main pump, but opening the main flow responsive to consumer unit demand, while, however, permitting continuous reserve pump flow to reach the consumer unit prior to such opening. A pilot stream from the main pump establishes a pressure differential on the valve to control response to main pump failure for cutting in the reserve pump. The pilot flow is through a pressure chamber means in which a drop in pressure due either to unit demand or main pump failure is effective to cause valve actuation for main flow opening, or valve opening for reserve pump flow. An important feature of the invention resides in the fact that the pressure drop is achieved either by loss of main pump pressure or reduction in discharge rate, e.g., due to a slipping drive belt of the main pump.</p> |
