| 摘要 |
<p>A hydraulic pump jack for hydraulically actuated well pumps of the general type having pistons driven in one direction to lift liquid up a delivery pipe and having the pistons returned to recharge the said pump, comprising a double-acting surface pump with one pump section arranged to communicate with a liquid delivery pipe extending up the well and the other section arranged to communicate with a pump control pipe which also extends up the well, and valve means connected to the said control pipe to open the delivery pipe to allow an outflow of liquid from the delivery pipe during the pressure stroke of the pump section connected to the said control pipe.</p> |
