Author Topic: Liquid flow indicator for very low flows - 1l/min  (Read 409 times)

Liquid flow indicator for very low flows - 1l/min
« on: 09 June, 2021, 09:37:48 am »
Long shot, but you never know....   our machines use a water/glycol mix coolant, but the normal flowrate is 1l/min. We currently use an electronic (electrostatic) flow indicator with a range of 0.5-20 l/min with a 0-5V analogue output (we seem just to monitor that, and if it gets too low, set an alarm) and a +/-2% FSD accuracy!. Unsurprisingly the results are often crap, and we end up throwing out 50% of what we buy, at £600 a pop. Now, as we only build 3-4 of these machines a year, and they sell for £350k, some take the view that spending £6k to get 4 good FI's is sensible ecomonics. It would be nice, though, to find a more suitable item - has anyone played around with very low flow rate FI's and know of one a less that £1k that'll do the job?

ETA: Apparently the switch has an RS232 output that we pick up a low flow alarm condition from, 0-5V isn't used.
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Re: Liquid flow indicator for very low flows - 1l/min
« Reply #1 on: 09 June, 2021, 01:03:33 pm »
How about a fluid with lower specific heat capacity? Pure glycol is about half the specific heat capacity - double the flow. Apart from that what is wrong with an impeller meter? Try badger meters (cannot be bothered to paste url

Re: Liquid flow indicator for very low flows - 1l/min
« Reply #2 on: 09 June, 2021, 01:10:46 pm »
What's circulating the fluid?  I assume it's a centrifugal pump?
And Darkness and Decay and the Coronavirus held illimitable dominion over all.

Re: Liquid flow indicator for very low flows - 1l/min
« Reply #3 on: 09 June, 2021, 01:24:08 pm »
OP reads as selecting a flow meter from a boxload to find one that just about works. How will that remain reliable?. If you just need a coolant fail alarm I have seen a design using a vertical  (clear) pipe containing a conical 'sinker' . Flow from below lifts the sinker. magnetic detection of position Sinker weight and relative bore scaled for flow range.

rr

Re: Liquid flow indicator for very low flows - 1l/min
« Reply #4 on: 09 June, 2021, 03:22:05 pm »
I have had good experiences of this type of meter —https://www.bronkhorst.com/en-gb/campaign-1/coriolis-flow-meter/?gclid=Cj0KCQjwzYGGBhCTARIsAHdMTQz2988EXgva0Hy2TNpnhcxcirpxUBJdcolBIOEPtLy7xzt42pfVg4gaAqsGEALw_wcB — though no at quite as low a flow as you are talking about.

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Re: Liquid flow indicator for very low flows - 1l/min
« Reply #5 on: 09 June, 2021, 03:46:24 pm »
A coriolis flow meter would probably be your best bet at this flow rate. I've been out of the field for a few years so can't give any up to date recommendations, but there should be plenty of possibilities out there.

Re: Liquid flow indicator for very low flows - 1l/min
« Reply #6 on: 10 June, 2021, 11:02:43 pm »
I can't find the link now. I was talking to Polish company a year or so ago about getting a fuel flow sensor for one of my UAVs. I need down to 0.3l/min and they had just that. They had a fairly big range of chemical resistant sensors.

Tried to search my inbox, but no luck.

Re: Liquid flow indicator for very low flows - 1l/min
« Reply #7 on: 17 June, 2021, 04:20:51 pm »
In my industry we often use IFM SM Model flow switches to measure flows of water at <40l/hr. These switches can be set with high or low flow alarms with a digital output, we use them to monitor the flow to a water quality analyser and alarm if the sample flow fails. I don't know if they will work with your glycol mixture.

Here is a link to the RS catalogue https://uk.rs-online.com/web/p/flow-controllers/0488093/