| 摘要 |
<p>A pump system is disclosed which operates at high efficiency in either a high volume, low pressure mode or low volume, high pressure mode. First and second internal gear pumps (124, 122) are driven by a common drive shaft (134). The first pump (124) has a smaller displacement than the second pump (122) and both pumps deliver pressurised fluid to a common discharge passage (154). An unloading valve (128) is operative to dump the output of the second pump (122) in response to fluid pressure in the discharge passage (154) so that it delivers fluid to the load device only when the pressure is below a predetermined value. The unloading valve (154) also performs the function of a low capacity accumulator. A check valve (178) is provided to prevent back flow in the outlet of the second pump.</p> |
