RobH | 18/08/2017 14:44:10 |
6 forum posts 1 photos | 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 |
JasonB | 18/08/2017 15:22:50 |
![]() 25215 forum posts 3105 photos 1 articles | The vacuum is actually what sucks oil into the cylinder as the upward moving ram uncovers the hole.
Edited By JasonB on 18/08/2017 15:26:08 |
RobH | 18/08/2017 15:59:22 |
6 forum posts 1 photos | Thank you Jason. So the spring must be sized to fight this vacuum. I suppose one could add a second check valve and flow path into the chamber (from the reservoir) to lighten the spring. Also, I worry that oil cavitation may be an issue at high vacuum. Apologies if I am overthinking it as operation at this scale may not warrant the added complexity and concern. Thank you again. Edited By RobH on 18/08/2017 16:04:20 |
Jeff Dayman | 18/08/2017 17:09:02 |
2356 forum posts 47 photos | Hi RobH - you have a private message. JD |
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