Vac depth will define output for a given temp, but it has a depreciating relationship… beyond 10^-3 torr to 10^-5 torr there a 10C difference, beyond that all the way to 10^-10 torr there is only a 2C difference…
Thats output based on bf temp for a goven vac depth…
Depends what vac depth you were at with one alcatel… and what their ultimate vac was at, youre talking about a pump that is really less then 20 cfm max… were you on a wide bore or gl, because if it was gl, thats like trying to suck cement through a garden hose… you wont see a difference… summit usedd to… maybe still does… supply an edwards 80 for 20L with gl… almost no difference between it and an e30… for vac depth on the system… the reason being is the orofice size… just because you have 56 cfm doesnt mean it can draw through a small tube…
Also if you run one alcatel up to heads and get it super dirty, then open the other, youre only going to get a difference of vac between the 2 ultimate vacs now… so say you dirtied the first pump up to 75micron, and the other is fresh at 10 micron, youll get like a max of 40 micron… so it doesnt seem like much… but if you lock off that dirty vac… you may get 13 micron… you need to know the health of a pump to use it to your advantage… “stethoscope your pump” put a gauge on it to test it beforw each run. Know its saturation depth at the end of the run… and work around that…
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I don’t think it’s greater depth that we are looking to achieve with two cheap dual pump setup. You are essentially limited to the vacuum depth of the worst pump when running them in parallel. You might be able to get down a little lower then the worst pumps lowest vacuum depth but it’s the greater CFM that we are after.
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These comments are based on opinion and “booksmarts” obviously not experience . . . and having used multiple pumps together it proves that the naysayers here have no practical knowledge or experience in this field.
I’m not suggesting everyone to go out and get 2 or 3 edwards 28 or 30’s to get deeper vacuum, but overall the lower I can get the vacuum throughout the whole process the lighter the product I end up with.
Post a pic of a setup with only a single pump then post pic of same setup with deeper vacuum running parallel pump setup.
If you want to use a pump as the volatile eater then that makes sense but if you think you are reaching deeper vacuum running parallel pumps then you are mistaken. Only running in series can achieve deeper vacuum and that takes two different types of pumps.
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That’s a little silly to tell somebody that something won’t work when they obviously have never tried it for themselves! Like I said the naysayers have no experience but still want to argue! I’ve already run that experiment so I have actually seen the difference in getting deeper vacuum levels. A pic proves nothing! One would need to take video to prove what was actually going on, showing the readings with 1 pump and then adding a second and then watching the gauge etc. and since I’ve already done this it’s on you to prove to yourself that you are mistaken. But then on an aside, you also recommended for me to purchase a Welch CRV16 when I called to order the best pump to run a 10 liter! Lets do the math here . . . that works out to 1.2 CFM per liter . . . more along the lines for recommending for a 2 liter.
Beaker had the right idea and the best setup for his size running some horsepower for his little rig, and was able to distill down in the 130’s and make some of the purest distillate as a result of high ratio of cfm’s per liter and the fact that the EM28 pulls under 1 micron, so yes it IS about CFM’s to liter ratios, and it does put deeper with 2 than just 1. I just need to get a few more parts and start running my diffusion pump!
If you can’t hold a scientifically sound argument then I have to resort to asking for evidence of what you are describing and trying to figure it out for myself. I have run with multiple pump types, sizes, and plumbing configurations and I have never experienced any appreciable difference in vacuum with parallel pumps. Maybe what you are doing is unique or some error in the way you are measuring. Not sure.
As far as vacuum pump sizing the crvpro16 is the sweet spot for a 10L. If you oversize the pump you have to oversize your condensing power or risk wetting the pump and it generally provides little to no improvement in vacuum. This can be overcome by throttling a valve but I can’t assume everyone has one or knows how to use it. If you want to buy an oversized pump for your setup we will sell you it but not trying to gouge people.