This is an internal gear pump with helical gears. It runs completely silent if powered by a BLDC motor. The basic pump consists of casing, inner rotor, outer rotor and end cap. You will need to find a 3-3.3mm metal shaft with a length of at least 35 mm. The shaft is heated to ~~270C and pressed into a well prepared slightly undersized hole in the inner rotor. 

 You can scale the basic pump up or down depending on use-case or use it in its original intended environment with the adapter for submersion in a jar. There are also two more adapters for two different types of motors that have the torque to reliably spin the shaft and two alternative couplers for 3.5mm and 5.5-6mm motor shafts. The couplers are designed to be printed out of TPU. If the coupler slips on the shaft then pre-heat the shaft above ~~230C and quickly slip on the coupler.

The jar dimensions are roughly 10-12mm height and exactly 52mm hole diameter in the threaded section zone.

Parts are held together by basic self-tapping screws for plastic assemblies. Bore and drill the holes according to the size of screws you have at hand.

To hook it up to a flexible pipe you need to add an adapter. I used a 3cm section of plastic tube from a used-up deodorant bottle. It has an inner diameter of 3.2mm and outer one of 4.3. You can glue it in place with hot glue or a 2-part epoxy resin.

The pump casing has a small cone chamfer on top of the shaft pass-trough hole to allow for a small sealing ring. It fits a very tiny silicone ring, which I slip on with a drop of lubricant oil. it seals the fluid in the jar when not pressurized. 

The shaft used for this pump is commonly found in CD/DVD drives for the 3.5 inch bay of an old computer. (The optical mechanism slides on 2 3.2mm stainless steel shafts)

The BLDC motors in the pictures can be sourced from either an old VHS player (capstan motor) or an old toner-based paper printer (paper feed mechanism motor). VHS player capstans run on 12V, so a fitting solution for older 12v based printers. Paper feed motors always run on 24V, so they are direct drop-in solution for new 24v printers. Most of these motors can run on 12V fine anyways. If you can make the proper adapter you can even try a microwave oven fan motor, a washing machine pump motor and other high starting torque motors.

Preferably you can print the whole pump  and its adapters out of TPU 95A or harder, but any other material will work just as well, as long as you can provide a good shaft-coupling solution. The pump in the pictures is printed out ABS, which is worst-case scenario for wear resistance and is still more than enough to get the job done. So far PLA, ABS and TPU have proven to bond perfectly to pre-heated stainless steel shafts. I recommend printing the rotors at a very low layer height, as it has a surprisingly good effect on the quality of vertical features (arguably more important than nozzle hole diameter).

See the pump in action: [https://www.youtube.com/watch?v=0sNQpEGsBV4](https://www.youtube.com/watch?v=0sNQpEGsBV4)