vacuum??

Check the cerebral cortex of your nearest politician. Chances are 1 out of 3 that you will find your perfect vacuum there.

Actually, it really depends on your definition of vacuum and the volume you constrain your measurement to. Or, talk to one or two particle physicists and they may tell you that there is no such thing as matter after all.

alwayslearning,

The thing is, you start with atmospheric pressure, which can vary depending upon location, altitude, and weather conditions (approx. 760 mm Hg, or 29.92 inches Hg, or 1 atmosphere, or 14.7 PSI, whichever you prefer). This is a positive pressure...

When a vacuum is drawn, you are subtracting from atmospheric pressure, therefore, you are looking at a negative pressure relative to atmospheric pressure.

Ok then, is it possible to have a negative atmosphere pressure below 0, or is the value infinite 0.0000.......1 reapeating. So I agree relative to the atm of 1, it is a lower value but not mathematically defined as a negative integer...am I wrong..

No. At zero you have no pressure. Just like Absolute Zero temperature. The is not negative Kelvins.

There is no such thing as negative pressure (unless relative to atmospheric).

It's a common missconception that you can suck harder and harder vacuum... you can only suck to atmospheric pressure... you can blow to many atmospheres.

I work for a company that makes peristaltic pumps, I'm always having to explain that you can pump to a greater head than you can suck. e.g our pumps go upto about 3 bar, but only suck to approx 1 bar. Which is why a peristaltic pump should have as short an input pipe as posible and have the long pipe on the outlet.

Del, I can see the advantage of a short input pipe but the output pipe puzzles me! To limit the possible effects of pipe deformation when pump is working you have a short pipe, but at the other end of the pump, How does the long pipe aid the pumping process?

LOL.... can't tell if you are joking!

No I didn't mean it has to be long....!

Just if you have to pump 30metres.. then have 5m at the inlet and 25 at the outlet.

Although the ACME pipe company might say longer is better .

As a general rule the distance you need to pump is 1 metre longer than the pipe you have to hand!

Del

Del, I was on a totally different planet when I read your last post! I get what you are on about now! Totally agree, a pump can push more than it can pull so to speak!

so, sorry for being a complete berk and lets leave it at that eh!

thank you for all the input...and I understand...good example for on the pumping system..

I'm a little late on this (was out of town for a week, with no access to the 'net ).

Pressure is always measured relative to another pressure. Gage pressure is measured against the surrounding atmospheric pressure (i.e., the air pressure on the outside of a pressure vessel). Gage pressure units have a "g" at the end so "psig" means "psi gage".

Absolute pressure is measured against -1 atmosphere or -14.7psi. However, absolute pressure takes -14.7psi to be the zero point. Therefore, -14.7psi is equivalent to 0 psia (psi absolute).

In a nutshell, a negative psig reading is a vacuum and a psia reading of less than 14.7 is also a vacuum. The answer to your question, therefore, is YES...if you're dealing with gage pressure.

If I have not confused you enough, please feel free to say so and I will do it again.

This was my first time using this website, and the response from the responders is great, answers and humor...I thank you all and will defintely continue on learning and using CR4..