Making a manometer

[Sparrowhawk]

This should go in the primary school boffin's corner but we don't have one of those, so come and laugh and point fingers at my failing here

 

I was using my blower door on a small room and thought I'd see if I can measure the vacuum created.

 

I grabbed some flexible pipe, water and food colouring, popped the pipe through the door and about 12cm up both sides. (The bubbles disappeared within minutes)

 

I left the fan running on full for 10 minutes. The water did not move. Not even 1mm.

 

There are air leaks in the room which I was sealing, but I don't think there are enough to equalise the pressure. I'd taped over an opening into the neighbouring room and the plastic was straining at the tape so the pressure was different.

 

So what's wrong here?

[RobLe]

Generally people aim for 50Pascals of air pressure, which is 50N/m^2.  That's equivalent to the pressure exerted by just 5mm of water imbalance.  It's not a lot!

 

What I would suggest though, is have the water in a loop all indoors, then measure the height difference between the levels.  The ends of the pipe need to be at different pressures - so put one end indoors, the other end outside, and make a loop with fluid all at your side.

You can put the pipes at an angle (say 45degrees from vertical), so it's easier to measure as the fluid levels are further apart, even though the height difference is the same.

 

I'm glad you said it was food colouring 😝

Edited March 3, 2023 by RobLe

[Sparrowhawk]

10 hours ago, RobLe said:

I'm glad you said it was food colouring 😝

I wish I'd used "the other liquid". Got some on the carpet and having a devil of a job getting it out. Good thing the wife is away for the weekend 😳

[SteamyTea]

10 hours ago, RobLe said:

I'm glad you said it was food colouring

 

6 minutes ago, Sparrowhawk said:

"the other liquid"

Could have tested it.

 

https://sitn.hms.harvard.edu/flash/2018/pee-pregnant-history-science-urine-based-pregnancy-tests/