Re: vacuum pump

>When this thread started, I tried my water bed aspirator with a vacuum guage. 
>I only got to 15 inches of vacuum and it had a nasty habit of injecting water
>down the vacuum line.  Maybe mine was bad, but one should be cautious about
>these cheap devices.  they are definitly far short of the fancy lab grade

Vacuum sucking devices (the ones you connect to water supply, so called "Jet
Injectors") indeed have a nasty habit of letting some water to the vacuum line.
happens whenever preassure drops quickly at vacuum side. Unfortunately this
also when you decrease the amount of water running (not enough sucking force).
Water should be turned off *very* slowly in order not to get water to the

Beware of the preassure changes in the water supply. If water preassure
decreases (less water running) system will suck some water immediately.

The usual precaution for this problem is to use a so called Wolf's bottle. It
is a device
where one line comes in and one goes out. If some water is drawn into the
it will drop to the bottom. Vacuum line is connected to another connection
will still be way above the surface of water. Therefore no water goes to the
line. This simple device will therefore protect the vacuum system.

Absolute preassures in the range of 10mmHg or so are common to this kind of
vacuum pumps. It will never go below the vapor preassure of water at the
water is in. Below this is never possible.

Harri Suomalainen