niobium - 22-11-2005 at 11:54
Hello. Swin is in need of some advice.
Swins got 2 rotary vane vacuum pumps which pull between 21-25 inch/Hg each.
Swin wants to somehow connect these 2 togather so they will pull more when run togather.
Swin was thinking of either connecting them inline (so that one will pull the other) or to make a T type adaptor and connect the T adaptor to the
vacuum flask.
Can anyone comment on this ? Is this doable? Is it safe?
THANKS!
hinz - 22-11-2005 at 12:30
If you connect them inline they will generate a higher vaccum. How much more is difficult to say, you have to try it.
If you connect them paralell via T adapter, they will pull more air (by the same time, then with one pump) out of the system you evaccuate. But the
worser pump will regulate the pressure more or less,so if one pump pulls 20inch Hg and the other 50 inch Hg you'll get not more than 45 inch Hg,
because some air can enter the vessel, which you are evaccuating through the worser pump although the better pump pulls more vaccum.
So connecting to pumps paralell isn't better, if the time to pump the vessel out doesn't matter.
It should be doable, if you don't use the pump for something for which it isn't made for. I once killed a frigde pump by trying to improve
the flow of chlorine trough my apperatures.
[Edited on 22-11-2005 by hinz]
niobium - 22-11-2005 at 12:51
thanks hinz 
swin very much appreciates ur thoughts
mick - 22-11-2005 at 14:25
nobium
It is the same as batteries. If the two are in line they pull more but if the one goes down they could both go down. If they are in parallel they will
pull less but more capacity and if one goes down the other one might keep working.
mick
bio2 - 22-11-2005 at 19:08
Pumps being equal parallel is twice capacity same pressure and series is twice pressure same capacity.
However in the case of vauum pumps the ultimate pressure is limited by design but intermediate pressures would see flow (capacity) improvement even
in series operation as the flow rate drops drastically as the pressure drops.
Free air ratings are rather meaningless and the best rotary vanes for example will pump 2 or 3 times the air at low pressures than the same free air
rated cheapo pump.
So depending on your application you could see dramatic flow increases but it's doubtful that any lower ultimate pressure will be achieved. A
continuos operating high loading dessicator would be a good application but vacuum distillation maybe not unless one pump can't remove enough
vapor for the desired take off rate.
Magpie - 22-11-2005 at 20:05
Full vacuum is 30 inches Hg. You can't get any better than that. I'm getting 28" with my water driven aspirator right now as the
water is winter cold.