# Negative Pressure in a 10mL syringe containing 2.5mL water

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1. Jan 20, 2016

### Morgan0415

Hello All,
We are trying to convert a vacuum leak test for medical devices (catheters) from a syringe based test to a pump based test.
The current guidelines call for purging air from the ID of the catheter under test with water (~1mL). The distal end of the catheter (tube) is blocked and the proximal end is attached to a 10mL syringe containing 2.5 mL water.
When the syringe plunger is pulled back to 10mL, what is the pressure in the syringe/catheter?

I assume it will change over time as the water evaporates but the test only lasts for 15-30 seconds.

Would the vapor pressure of the water come into play? Would it be 0 mmHg even with H2O present?

Thank you for any information you can provide.
Morgan

2. Jan 20, 2016

### Staff: Mentor

15 to 30 sec is certainly long enough for the water vapor pressure to attain its equilibrium value.

3. Jan 22, 2016

### Morgan0415

Thank you for your quick response. Unfortunately, it went to my company "clutter" box so sorry for my delay in replying.

So does that mean we should use 0 mL as initial volume (Vi) and add the vapor pressure of water to the final pressure (Pf) achieved (PiVi=PfVf)?

...or should we use 3.5mL as Vi and add the vapor pressure of water to Pf?

Thanks again.

4. Jan 23, 2016

### Staff: Mentor

I'm having trouble understanding your question(s). Would it be possible to provide a diagram (or diagrams). Thanks.

5. Jan 25, 2016

### Morgan0415

I hope this helps. We would like to know what the pressure is in the syringe on the right after the plunger is pulled back to 10mL. Please let me know if more info is needed. Thanks again.

6. Jan 25, 2016

### Morgan0415

Total water volume = ~ 3.5mL (1mL in catheter and 2.5mL in 10mL syringe attached to catheter)

7. Jan 27, 2016

### Staff: Mentor

The pressure will be the equilibrium vapor pressure at the temperature of the liquid.

8. Feb 1, 2016

### Morgan0415

Thank you very much!