Re: vacuum pump

To: tesla-at-pupman-dot-com
Subject: Re: vacuum pump
From: "Harri Suomalainen" <harri.suomalainen-at-pp.inet.fi> (by way of Terry Fritz <twf-at-verinet-dot-com>)
Date: Thu, 25 Mar 1999 20:46:28 -0700
Approved: twf-at-verinet-dot-com

>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
>devices...

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.
This
happens whenever preassure drops quickly at vacuum side. Unfortunately this
happens
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
vacuum
line.

Beware of the preassure changes in the water supply. If water preassure
suddenly
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
bottle
it will drop to the bottom. Vacuum line is connected to another connection
which
will still be way above the surface of water. Therefore no water goes to the
vacuum
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
temperature
water is in. Below this is never possible.

Harri Suomalainen