Author Topic: Sufficient vacuum pressure?  (Read 1332 times)

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MisterWize

  • Guest
Sufficient vacuum pressure?
« on: December 07, 2003, 08:30:00 PM »
Swim was wondering if this water pump connected to a glass or stainless steel aspirator will suffice for all lab applications (eg. vac distillation of key products etc etc).
Will a glass one make any difference to the strength of the vacuum?

The pump itself has maximum height of 35m and can pump around 32 litres /min?  can anyone help on this as I have done some basic reading on this but little has helped.

Mw


homeslice

  • Guest
How much Horse power is the pump?
« Reply #1 on: December 07, 2003, 09:57:00 PM »
How much Horse power is the pump? I think 3/4 hp are recommended.

Swim used to have an aspirator set up for vac distill but since returned his pump and bought a used vac pump that works MUCH better. Swim thinks he spent more money on ice to keep the water in the aspirator bucket cold than he spent on a whole new pump. That whole aspirator setup was inconsistent messy and loud as fuck. Take a look at ritchie yellowjackets which kinda resemble a bee  :)  if swim changed ur mind about aspirators. They're about as much as an aspirator, water pump, pipes, ice and the rest of the set up on our favorite auction site...  :)



Prince_Charles

  • Guest
Europe
« Reply #3 on: December 08, 2003, 03:39:00 PM »
Vacuum pumps are much more expensive in Europe. However, you can construct a water-jet pump station in the UK for £ 60 or so.

I compared the specs on several different laboratory water-jet pumps (aspirators): they required between 10 and 15 L/minute at between 1 and 2 bar (10-20 m hydrostatic head). The glass water-jet pumps don't seem to be any better in performance. Bibby-Sterilin polypropylene pumps seem to be as good as any.

You can run (at least) 2 jet pumps from a water pump of that capacity.

You can estimate the pump power required as follows (but this is secondary to the pressure and capacity requirements):

e.g. 10 L/min at 1.5 bar

SI Units (sorry Americans):

10 L/min = 0.167 L/s = 1.67*10E-4 m3/s
1.5 bar = 1.50*10E5 Pa

Power = flow rate * pressure drop = 1.67*10E-4 * 1.50*10E5 W
      = 25 W

Double power to allow for losses in plumbing

Power = 50 W

Assume pump has 50 % efficiency

Pump electrical power = 100 W (1/7 HP!)

Using too big a water pump and running the jet-pump at too high a flow rate won't increase its vacuum any further and will just dump more heat into the water.

I was wondering whether to try running the water pump from a motor controller to reduce the effective power.


Prince_Charles

  • Guest
A water jet pump (aspirator) like this:
« Reply #4 on: December 09, 2003, 10:23:00 AM »


And this is a pdf page from a catalogue with various jet pumps:

http://www.geocities.com/wolfgang_boxhead/apps1027.pdf



I haven't measured the pressure of the set-up yet but it sucks like a tart on Hugh Grant's organ.

I was thinking that if Yankees are using waterbed pumps that perhaps these are not as efficient as a laboratory pump and need more pressure and water flow to get a decent level of vacuum. I haven't managed to find a waterbed pump in the UK but then not as many Britons are sufficiently obese to require 10 hours a day lying in a flotation device.


BieneMaya

  • Guest
I bought my high power vac pump used
« Reply #5 on: December 11, 2003, 04:45:00 PM »
I bought my high power vac pump from an online auction.

Ok it was sold as defect. But there was just
a little corrusion in the inner pump.
So I got it for about 30 $ incl shipping.

It destills my sassy at about 90 Celsius.

Look out for that old pumps.
Either the engine is defect and can be easily replaced
with some other old e- engine
or there`s just a little corrusion in the pump
that makes the enginepower unable to break through.

But you can clean it and everything`s allright then.
It took me just two hours.

baalchemist

  • Guest
Most used high-vac pumps that are apparently...
« Reply #6 on: December 15, 2003, 09:37:00 AM »
Most used high-vac pumps that are apparently 'seized-up' and sold cheaply, are easily repaired. Seizure is usually just a broken vane spring or the little shaft inside the spring is the culprit, also chunky sludge in oil compartment can cause binding. Easily replaceable vane springs & shafts , plus a good internal cleaning will get those old Cenco's & Welch's returned to duty once again.