Henry Wycliffe and the Edwards Dry pump

Henry Wycliffe – A Hero of Vacuum


Henry WycliffeHenry Wycliffe joined Edwards in 1953 and patented the Edwards Dry Pump in 1984. Discover the origins and significance of the pump in this extract from a conversation that took place between Henry Wycliffe and Andrew Chew.


Andrew Chew (AC):  At that time (1980's) wet pumps were still being used, so how did the programme for dry pump development start? 

Henry Wycliffe (HW): With diffusion and rotary pumps, there is a problem with migration (back diffusion) of oil vapours into the processing chamber; one can stop it with cold traps and so on. There was always the need to try and reduce backstreaming.

AC: So in the 1970's you had a two stage pump with one stage oil lubricated and one stage dry?

HW: We built, tested and applied for a patent for this design. The pump worked but it did not come to fruition; it was a half measure... We also studied screw pumps for possible use as dry pumps. The manufacturing technology hadn’t progressed yet to numerically controlled machining.

AC: I notice here you actually submitted the application for the patent in 1967...

HW: Having looked at screw pumps, and compared them with Roots blowers, there was not enough displacement for the size and weight of this design, so we abandoned this approach.

AC: But this was in 1971 and you were looking in principle at dry pumps even then?

HW: Yes, at the Northey claw principle which is quite old and unique. There is a paper, which I presented at the American Vacuum Society in 1986,and which explains the reasoning that lead to the design of our dry pump - combining the Roots principle with the Northey claw mechanism. Mr. Northey developed the claw mechanism around 1929 as an internal combustion engine, with spark plugs, and  invited people from Ford Motors to demonstrate its performance.


Henry Wycliffe visit to Burgess Hill

Henry Wycliffe with the Dry Pump during a visit to Burgess Hill 


AC: When did you realise this (dry pump mechanism) was going to be a big rather than just another development?

HW: I didn’t. As I said, it was the semiconductor field that made the pump succeed. If it weren’t for the use in microelectronics, the manufacturing cost at that stage being high, meant the dry pump wasn’t competitive as compared with the cost of rotary pumps. But, since then, production machining at Edwards progressed tremendously. Before, there were problems producing complex components/ profiles. Advances in production technology widened possibilities. There are now regenerative compressors made by numerically controlled machines (used in the Edwards EPX pumps). Dr. Neil Tenwick and I went to the Oxford University to evaluate a regenerative compressor; that was early days. The intention was to replace Roots blowers but not to deliver to atmospheric pressure. These were compressors but we were interested in high pumping speed at lower pressures. We discovered that these machines lose performance rapidly at low pressures, especially with light gases. Working on mass transfer principle, compression drops as there is little mass at low pressure.

To read the full transcript, click the link below:


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