Peristaltic pumps are best because they are positive displacement devices. They work by using a 2 rollers to squeeze a section on tubing and force the contents out -much like you get a freezee out of it's package by squeezing your fingers together and sliding them up it's length !
The difference is that in this case, the tubing has 'memory' and opens back up as the roller passes, sucking more fluid in so the process continues.
If you know the cross-section of the tubing and the radial distance between centres of the rollers then you can know *exactly* how much liquid will be dispensed per rotation of the head assembly. The motors on these pumps are run through a planetary gear train to reduce the output shaft speed so it's much easier to control dosing by timing the motor run.
The tubing used is a key element. It must be of a special formulation that retains its' shape after repeated squeezings. Various types are available for dosing different chemicals. The best part is that whatever is being dosed never comes into contact with any part of the pump.
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-Mark
29 Gal Bowfront w/24" LED Lights. DIY HOB Sump (5.4 Gal) MP40. Orange Spotted Watchman Goby, 2 Clownfish and a few hermits.
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