It appears that you believe this setup will flow 9 liters in 30 minutes. Perhaps I missed the data but I thought there was significant variation between tests. Perhaps I am wrong?

this setup will flow 9 liters in 30 minutes, +/- variation in the tubes. I worked to isolate that variation to the tubes, and @gretchengehrke and @nickshapiro can speak to why we don't think that is super important, given published literature.

Upon return I'm planning on checking the flow of all the used tubes and the kit to look at variation and drift, although I'm not expecting any drift.

Then my other concern is how does the used tube flow rate change over several days or weeks since there are chemical reactions occurring that might change the restrictions? I believe you have some tubes you measured some time ago. Can you compare the flow restrictions now?

This looks great! Maybe they could also mark the two solid black lines in addition to the color change so there is less ambiguity on the measurment? Also, Dan, I belive mathew has tested old tubes flow but found no variation over time.

Looks nice. I had an idea for an alternate gas volume measurement technique whereby you connect the exhaust side of the pump to a deflated bag then stop sampling when the bag is full. With this technique you wouldn't need to measure the flow as accurately--you just sample until the bag is full and then the sample volume is dependent on the size of your bag. The ideal inflatable would be something like one of these tedlar gas sampling bags because they're both durable and rigid--they don't expand like a balloon. Example, $25 each http://www.zefon.com/store/zefon-tedlar-gas-sampling-bag.html

You would probably want to add a pop safety valve in line to prevent overfill and bursting ($8, mcmaster http://www.mcmaster.com/#standard-relief-valves/=xs6b2u )

I've never tried this but it might be a simpler approach. You would want to characterize the exact volume of the bag in the lab before use but it wouldn't have to be exactly 9 liters. You could do this by measuring the flow rate precisely then timing how long it takes to fill the bag. Once this is done I would think the bag would be the same volume provided it doesn't spring a leak.

I'm wondering if a $1 beach ball would work but it wouldn't be as durable. Yet considering the cost of the tubes you could afford to pop the beach ball now and then. You would need about a 10 inches diameter beach ball for 9 liter volume.

Just something to consider--maybe for a different, dirt cheap approach. I know public lab is always looking for cheaper approaches!

@DavidMack Now we're talking! I've done this before to measure higher volume airflow, but never thought to add the pop valve. I really like that. You could plug it in and time it until the valve pops. roll it up to evacuate and start again.

Here's my previous tests. This tube is measured so one foot of length = 1 cubic foot:

Me and my sister, being proud of ourselves for coming up with this:

So... I got involved with Public Lab in the first place because making balloons is my hobby. We have a TON of plastic seaming equipment here and making a custom-sized bag in volume is really not a problem at all!

Just ran my first test! Thanks for these great instructions! I would add a couple things to the instructions:

• As the power cord is less than a meter, please plan ahead to identify nearby electrical outlets and carry an extension cord if needed. (Future versions may include a battery pack!)
• The case will vibrate while the pump is running, watchout if you've placed it on a table or elevated surface where it could work itself right off the edge. Also, the vibration creates just a bit of background noise.

And a note for making the temperature conversion sheet better:

• Include one sentence -- in big font -- how to convert PPM to PPB (by moving the decimal 3 places). Yes, we have to include this.
• Below that, print wording to give some context for the numerical reading that this tool gives the user. Perhaps existing workspace regulations and research linking formaldehyde exposure (acute or chronic) to health symptoms, and explain that there are no regulations on home environments. Or however this should be worded.

Generally, it would be cool to understand more about how the Kitagawa 710 Formaldehyde tubes work. Is there a good note about that somewhere?

awesome! glad the instructions worked for you! I'm putting 2-meter cords in the newer prototypes. We won't be able to run these on battery power though.

Just if you use the volume of a bag keep in mind the Combined Gas Law.

Add the Kitigawa tube instructions: once you receive the kit in the mail, store the tubes in the refrigerator. Ideal 32-50 degrees F.

"When you are done with the test, slide the switch back to the right. This will prevent the batteries on the timer from being drained."

Consider using a detachable/reusable mounting system for the battery pack. I will look into velcro.

Here are some beauty shots of the next version in black. nothing much has changed except the locations of the buttons and inlets to accommodate a photo card. cut file: seahorse-box-plate-template3.pdf

@Mathew I like!

these are stunning @mathew!