# How long will the vacuum chamber keep sufficient negative pressure to pull back the p

1. Jul 9, 2012

### Neg. pressure

The syringe' plunger is in a fully retracted position (non-vacuum state) and is then connected to the tube forming an airtight seal. Then the valve to the vacuum chamber, having 29.9 Hg of vacuum, is opened.

I am fairly, certain that the plunger in the syringe will move to its forward most stop, on the first run. What will happen with the 2nd, 3rd, 4th, and subsequent runs, provided the vacuum chamber is not emptied after each run?

 Will the plunger be drawn forward on its tenth run?
 How will the pressure differential be affected after the first run, then the following runs?

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2. Jul 9, 2012

### Staff: Mentor

Re: How long will the vacuum chamber keep sufficient negative pressure to pull back t

Assuming minimal friction, the plunger will be drawn forward on its 10th run.

Assuming you allow the air to return to equilibrium temperature after each "run", you can simply ratio the volume added to the total volume to find the pressure. Ie, after 5 runs, you've added 500 cc of 1atm air for a pressure of 500/1000=.5atm.