| 摘要 |
A positive displacement pump system has first and second delivery passages for the pumped fluid and a main discharge passage. A control valve operating in dependence on the pressure drop across an orifice in the discharge passage diverts through overspill porting a proportion of the flow through the second delivery passage, the remainder added to the flow from the first delivery passage and passed to the discharge passage. The control valve also regulates the by-passing of a proportion of the flow from the first delivery passage to the overspill porting. As the said pressure drop increases, the control valve first increases the proportion of the flow from the second delivery passage diverted to the overspill porting and, as the pressure drop increases further, then commences to by-pass fluid from the first delivery passage to the overspill port, the quantity by-passed increasing with increase of said pressure drop. For a given movement of the valve member, the increase of effective area of communication between the second delivery passage and the overspill porting is greater than that between the first delivery passage and the overspill porting.
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