BCO-DMO BlogInstrument: Zooplankton Pump - gas powered diaphragm
This kind of diaphragm pump, manufactured by Homelite and run on gasoline, is called a positive displacement pump because it pumps a specific volume for each pump cycle. Diaphragm pumps move fluids more slowly than centrifugal pumps but treat the animals more gently and they can handle thicker mud and larger amounts of solids. They also tolerate air being drawn into the pump and can be run dry without damage. In 2002, Homelite was acquired and became Riverside Pump Manufacturing, Inc. Diaphragm pumps feature a straight through self priming design and the rubber elastomer diaphragm and flapper valves are easily replaced on site.
EL9905: Pump samples were taken by attaching one end of a 5 cm x 60 m reinforced hose to the CTD/rosette frame so that the hose opening was near (within ~0.25 m of) the CTD sensors. The CTD was lowered to depth (usually 50 m) and stopped at discrete sampling depths at 5 m intervals up to a depth of 5 m. Time was given for the system to clear at each new depth before sampling. A gas-powered diaphragm pump delivered water from sampling depths to the surface at a nominal rate of 0.3 m3/min. This water passed into a small, rapidly draining reservoir (0.13 m3) on deck to dampen the surge. This reservoir also was drained between sampling depths. A 1.9 cm ID hose carried water from the reservoir to individual samplers equipped with 40 um mesh nets. An electronic timer and flow meter installed in the 1.9 cm hose was started and stopped for each sample, providing very high accuracy measurements of the volumes filtered. The final sampling rate averaged 13 l/min, and most samples were filtered from 27-33 l of water. Samples were preserved in 3-5% buffered formalin.
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