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Subject: Re: Vacuum pumps
Poster: Richard Hull
On , Richard Hull wrote:
I noticed that Richard had moved on to the belt driven pump which is rated if I'm not wrong at 6CFM and I was wondering what makes this other pump better than the smaller air-conditioning system?
>The big question is, if the move from the first pump to the other was a necessity or just a choice by Richard?
Pumps are pretty much pumps. AC and refrigeration pumps lie a lot and the CFM rating on them is overblown. They tend to get their rating through speed and not chamber volume. A 6 cfm refrigeration pump is probably an honest 2 cfm volume etc. Direct drive pumps run fast. They also wear out faster.
Old belt drive pump chug away at 400-600 rpm. Their plodding bluba..bluba...bluba is a lot less grating on my nerves than the continuous high speed roar of a direct drive pump.
For portable operation nothing equals the direct drive. They pump fast and if new or in great shape are superb pumps. I will note that the 6 cfm belt drive weighs about 110 lbs and the 6 CFM direct drive only 42lbs. Direct drives are not real good at continuous duty operation. Belt drive units are meant to be run for weeks on end.
The bottom line is that it was my choice and the base level on the old precision belt drive unit was a few microns lower than my direct drive unit.
I have 11 vacuum pumps in all now and use only 2 regularly. I have a superb 18cfm Edwards direct drive and a beautiful Welch 1397 17.7 cfm unit as well, but have never pulled a large vacuum in anger with either unit, just tested them for operation and base level vacuum. I have three Welch 1402's which I consider one of the finest belt driven pumps ever made by the hand of man. Again, neither pump has ever been used in action.
What I use is what I use. The geometry of the old 6 cfm precision fits the current shelf setup in the fusor III rack. I still haul out my old 6cfm refrigeration direct drive for quick and dirty checks of gauges, vacuum science demos, etc.
One thing is for sure. A blown or shot pump will never stop me as I will just shift one of the loitering 1402's into position.
When I go turbo, I hope to use the 1397 as the fore pump.