What I want to do
Create a version of the modified aquarium pump in the formaldehyde test kit that is flexible and can be adjusted across a widest flow range, and also protected from damage by particulates getting into the pump.
Matching commercial pump volumes
a DIY test kit:
A single-sided pump has difficulty pulling more than 300ml through a formaldehyde test tube. Modified on both sides, it is capable of pulling 2+L/m of air through a tube or ten times as much. Joining both sides seems to more than double the pump's capabilities, which can be adjusted from 100ml/m to 2L/m which should accomodate a range of testing tubes, and is the same spec as the $1800 Draeger X-Act 5000. The pump came with a "T" to plug both sides together:
Filters for reliability
The air pump comes with an intake filter by default, by modifying it to be a vacuum pump (pulling air) rather than a pressure pump (pushing air), we bypass this intake filter. While in limited testing the pumps have held their calibration, fouling will definitely ruin the pump long-term.
Most bio lab-grade vacuum pumps have 1um filters inside that are $100+, which is more than 3x the cost of the pump. This guarantees a clean airflow out the end of the pump, but if we're only concerned with fouling the interior of the pump, I think a courser industrial-grade filter will do the trick.
All the filters I found were for 1/4" hosing, rather than the 1/8" hosing that comes with the aquarium pump and fits the formaldehyde test tubes. I therefore had to order some 1/4" air hosing and two 1/8" - 1/4" reducer barbs.
here's what the air setup looks like:
Here are the additional parts to add to the pump's parts list: