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Or alternately what is the name of the device I'm looking for?

My first thought is to make a narrow V shaped chamber by gluing 1/4" acrylic together with 2 face plates and a mid plate with a triangular hole removed. The liquid comes in at the bottom and lifts a slightly heavier than water bead. Faster flow has to get further into the V chamber before it spreads far enough to match the net gravitational down on the bead.

At 10 liters per hour, flow through a 1/4" pipe is about 9 cm/s.

This seems like such a simple way to do it, I'm sure there are off the shelf ones available for a few bucks. But often searching depends on knowing what it's called.

flowmeter

This is one that I found on ebay, but intended for gasses, not liquids.

this sort of design with 2-4" plumbing is used for pneumatic seed sorters. However in those, you are indifferent to turbulence. For this application to have something reasonably repeatable, I think I need non-turbulent divergence.

Purpose: I'm trying to make a fertilizer injector with minimal pressure drop. Overall the notion is to put a slight constriction in a 3/4" pipe creating a small (few oz) pressure drop. Two small diameter hoses connect to the bottom and top of a chunk of PVC pipe with the fertilizer inside it. Since the pipe is pressurized to the line pressure, the differential across the constriction will move water through the device.

A small valve on the 1/4" line can be used to adjust the flow to put the bead at about the same place each time.

Another thought would be to use something like the IV drip chamber. This is a comparable flow rate. For long duration, I don't know if you could maintain air in the chamber.

Are there other effects I could use?

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  • $\begingroup$ The IV drip method is viable, although it does not technically "measure". It is a great way to produce modest pressures with some useful accuracy. That can be converted to flow with tube of controlled diameter. Note however error sensitivity to diameter is 1/D^4 $\endgroup$
    – Pete W
    Jan 14, 2021 at 1:37
  • $\begingroup$ with controlled supply pressure, an adjustable needle valve might be all that is necessary. fluid can be pneumatically driven, air pressure regulators are cheap. $\endgroup$
    – Pete W
    Jan 14, 2021 at 1:41

4 Answers 4

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I think you’re looking for a rotameter

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  • $\begingroup$ Good call. That was the search term I needed. $\endgroup$
    – Sherwood Botsford
    Apr 30, 2018 at 10:56
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They make these for liquid's also. Uually the bob looks like an upside down top hat riding on an rod inside the glass or plastic V tube. As mentioned above a rotometer will work but requires a voltage PS to convert the electromagnetic pulses into a Vdc output. -AG

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  • $\begingroup$ In this case all I need is a visual indicator. $\endgroup$
    – Sherwood Botsford
    Apr 30, 2018 at 10:56
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Try variable+area+flowmeter.

enter image description here

Figure 1. Various types of variable area flowmeters.

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As you're trying to measure small volumes would a volume marked supply vessel feeding your supply valve in conjunction with a timer (watch,phone or stopwatch) give you the answer you require? The only cost would be your time setting valve to required flow, which you'd have to do anyway with an expensive meter.

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  • $\begingroup$ This does not appear to be an answer. $\endgroup$
    – Mahendra Gunawardena
    Jan 13, 2021 at 19:23

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