Hi folks,
I have an equipment/engineering question:
Why is everyone using oil-sealed vacuum pumps?
Vacuum pumps are among the most diverse in terms of equipment choices: rotary piston, ejectors, rotary cane, mechanical boosters, chemical dry pumps, diffusion pumps, the list is quite expansive.
So why is everyone using oil-sealed, rotary cane Edwards pumps for distillation purposes?
I’d love to see response and see if I can’t propose alternatives
Rotary vane Gives the deepest vacuum for your Buck 
They are When oil is changed once in a while tanks
Small apparatus with high cfm
Diafragm lacks Many of the above
Piston has oil to
Most other pumps Need a backing pump
Dual vane pumps have two key advantages and several other smaller considerations. First of all is that the entire mechanism is virtually submerged in lubricating oil during its entire life. This reduces noise considerably but the advantage is that machinery submerged in oil will endure orders of magnitude more abuse than a machine that is not.
This means that I can freely allow my pump to gulp through it gases and such that contaminate the oil but have no real impact on the longevity of the pump. The worst case scenario in a dual vane pump is the oil becomes contaminated and must be changed. All other options capable of pulling down to at least the vacuum depth of a dual vane pump or lower require the system be designed so zero contamination makes it through to the pump. With a dual vane pump the cost of a lot of contaminate making it to the pump is an oil change. With say a dry scroll pump arrangment the cost of allowing contamination into the pump can be enormous and catastrophic.
Then pump mechanics of being buried in the lubricating and process oil allow for tight tolerances as well. The design of a dual vane pump makes it possible to routiney pull down to deep vacuum levels required for MFP flow conditions and pumps like diaphragm pumps or piston driven pumps simply cannot achieve such vacuum depths. A diaphragm pump is very resistant to contamination but even an 8 head diaphram pump cannot compete with my old EM28 for vacuum depth. Not even close.
A dual vane pump of proper design and ultimate vacuum depth capable is generally a very long life item, even if abused by repeated exposure to pump contamination. A piston pump will sieze if the oil becomes too contaminated because it relies on a viable oil film for internal lubrication of the piston instead of a submersed oil bath. A diaphragm is contaminate tolerant but cannot pull tight vacuums like a DV pump. Scroll pumps and the more exotic offerings designed often to be used in concert with one another can pull very deep vacuums but are enormously expensive to obtain and require very strict controls and much more hardware to implement and are intolerant of even mild contamination.
Beaker You should have be a wraiter and teacher Well said 
Once i read your explanations iT all is so clear
I admire your input and enjoy reading your " colum" thx for your patience and time
You are one of a kind 