1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Air Bubbles / Dunk Test

  1. Oct 21, 2009 #1
    Hi everyone,

    I want to measure the flow rate of air bubbles under water for a leakage test of air brake chambers. I mean i want to keep the flow rate of bubbles under the permissible limit of 10 cubic centimeters per minute, and i have only 30 seconds to do this because of the conveyor speed. I'm searching for a device/ method for days to estimate the bubble flow rate (or at least bubble cross sectional area), but i couldn't find it anywhere. Does anybody know how to measure the leakage rate?

    Thanks in advance,

  2. jcsd
  3. Oct 21, 2009 #2
    Hm , I would put the chamber in a mark glass or bowl full of water, then measure the change in the depth of water due to the air leaving the chamber and the water entering it. The change can be calculated and the time it took , then you can get the average amount of water entering / air leaving per second ect.

    Hope that helps! ( I think it makes sense ;))
  4. Oct 22, 2009 #3

    That's not possible for us to put the chamber under water totally, because it has ports for air inlet, and they shouldn't get wet. So, we put more than half of the chamber (bottom side) under water, especially to be able to see the clamp ring leakage.

    Spring and service brake chambers are cylindrical pressurized objects (about 8 bars), and we put them in water to understand if there is a leakage, i.e, pressure drop, from any side of it. There is not one specific point that we can put our sensor and measure it. Bubbles can form anywhere around the clamp ring. How can ve orient all the bubbles to one channel? What is more size of the bubbles are fluctuating continuously. So, counting the bubbles is not possible and meaningful for us. What i need is just the flow rate to approve or reject the product and i have only 30 seconds for this since test is done on the assembly line where the conveyor belt arrives & stays there for 30 seconds. I don’t know if you can help me or not, anyway thanks in advance.

  5. Oct 22, 2009 #4
    At guess you have been testing the chambers by dunking them in water to see if there are any bubbles but now have a new requirement to measure the leakage rate, if I'm correct, start from scratch. Connect a low flow flow meter into the hose that you use to pressurise the cylinders after the initial surge as the cylinder pressurises you can then measure the seal leak rate, with no need to get your hands wet. Two thoughts, you dont say whether your leak rate is in ACCm/min or SCCm/min you.ll need to sort that out to get the correct scale on the meter. If you can't do this in 30 secs redesign the work station so that two operators can work in parallel.
  6. Oct 26, 2009 #5
    leak rates are best determined by going to a set pressure, stabilize pressure (allow temp to equalize), record first pressure, wait X time, record second pressure. The rate is the difference between the two readings, divided by time. Many pressure controllers have functions already built in for this. Then you could lose the whole dunk tank.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook