Hello. My question concerns the free plan in the recent issue of Model Engineer magazine (No. 4567). I understand that oil fills the pump cylinder via the No. 60 inlet holes as the ram ascends vertically. When the ram returns and descends past these holes (blocking them), oil is delivered under pressure past the ball check at the bottom of the assembly. After the oil is delivered, the ram tries to ascend again via the return spring. However, as the inlet holes are still blocked by the side of the ram, and the lower ball check prevents backflow, I am unable to work out how the ram can ascend without a substantial vacuum developing. Perhaps there is an oil pathway I am missing, or perhaps, the oil flows into the expanding chamber via the ram/bore clearance?

I was wondering if someone on the forum could please clarify this. Thank you in advance. Rob H. New York, USA