| 摘要 |
<p>A hydraulic power pack for supplying hydraulic fluid under pressure for operating apparatus such as hydraulic workover units used in servicing oil and gas wells. The power pack provides substantially constant hydraulic power input to the driven apparatus over a wide range of pressures and flow rates. The power pack includes a constant speed engine, a gear box driven by the engine, a bank of positive fixed displacement pumps of varying sizes driven by the gear box and having discharge ports connected with a common discharge manifold, a hydraulic fluid reservoir, an intake manifold between the reservoir and the pumps, a return line to the reservoir, a recirculating line connected between the discharge from each of the pumps and the return line, and an unloading valve in each of the recirculating lines operable responsive to the pressure in the discharge manifold for recirculating each of the pumps to the reservoir at a predetermined pressure value. Each of the unloading valves is set to open at a different pressure ranging from a minimum at which all of the pumps discharge to the discharge manifold to a maximum above which all of the pumps recirculate to the reservoir. The unloading valves are set to operate in graduated sequence with all the pumps discharging to the manifold below a first minimum pressure with one pump automatically recirculating to the reservoir as each predetermined pressure increase increment is reached until at the last operating stage only a single pump is discharging to the manifold and above that stage all pumps recirculate to the reservoir. The power pack permits operating a hydraulic workover unit automatically providing maximum lifting force at a minimum speed to minimum lifting force at a maximum speed.</p> |
