Measuring air flow via gauge

M

Mark DM

Screwfix Select
I have a small air compressor in my garage supplying air to my treatment plant around 10m away. I would like to incorporate an air flow gauge into the rigid air supply pipe, either connected directly inline ( think pipe is about 25mm) or external to the pipe with some kind of sensor within the air flow. Having a gauge will indicate the pump performance and highlight any blockage at the outlet within the treatment chamber... looked online several times to try and find something suitable at a reasonable cost but just can't find anything other than really expensive Industrial kit. Wondered if anyone on the forum had any ideas or suggestions as to something that could be used. I was hoping there would be a gauge similar to an air pressure gauge with flow sensor that I could fit by drilling and tapping into the rigid pipe. Thanks.
 
Thanks for the reply, I will take a look. I'm hoping to find something that will give a fairly accurate indication so I can respond if I see flow reducing.
 
Mark DM said:
Perfect :)
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What flow in l\min and at what pressure? Assuming it is pretty low.

For example up to 25 l\m at 14 psi but this would have to be in line of course. Only a fiver.
https://www.amazon.co.uk/2-5-25-Suitable-Measurements-Measuring-Oxygen/dp/B08BJV8T9P
519ZmzL16ZL._SL1001_.jpg
 
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Hi, Muzungu, its pretty low at 0.15 bar and 60lt pm. I have seen similar to your suggestion. What concerned me was that the pump outlet flexible pipe is 18mm and connects into a rigid pipe around 25mm. Connecting in and Using this type looked as though it would severely restrict flow. I was hoping to find something like a standard air pressure dial gauge with maybe a sender unit that could be fitted into the rigid pipe and be left in place to continuously monitor. Thanks
 
Your car measures air flow by passing the intake air over a hot wire. The input temperature of the air is monitored. As the cool air passes over the hot wire it cools and the electrical resistance falls. The ECU does the maths.
 
Mark DM said:
Hi, Muzungu, its pretty low at 0.15 bar and 60lt pm. I have seen similar to your suggestion. What concerned me was that the pump outlet flexible pipe is 18mm and connects into a rigid pipe around 25mm. Connecting in and Using this type looked as though it would severely restrict flow. I was hoping to find something like a standard air pressure dial gauge with maybe a sender unit that could be fitted into the rigid pipe and be left in place to continuously monitor. Thanks
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Anything other than a simple rotameter is going to be quite expensive as it requires electronics. As @Bob Rathbone says the Mass Air Sensor in cars need sophisticated electronics to both power the sensor and then interpret the results. In your case a display as well.

Here's a company that can supply a 100 l\m rotameter with a valve to adjust the flow for £110. You may well find a cheaper Chinese version with a bit of searching on ebay.
https://www.poddymeter.co.uk/products/flow-meters/variable-area-flow-meters/
 
You could use an orifice (a hole in a small plate in the airflow) and measure the pressure drop across it, that will be proportional to the flow rate.
 
You don't need a flow gauge, just a pressure gauge. During normal duty there will be a back pressure which you can mark on a suitable pressure gauge as the norm. If anything becomes blocked the back pressure will change. If you can find the duty curves for the compressor the back pressure will show the flow if plotted against the pressure.
 
Thanks Mr R. I can give that a try. I do have a pressure gauge reading low numbers. 0- 15 psi it is so may well pick up a back pressure . If it won't then I can go more sensitive
 
I presume with a pipe of 25mm this is not high pressure compressed air, but some sort of blower? If it's a centrifugal compressor it'll likely have a duty back pressure of 3-6 psi so you should get a reading on that 1 bar gauge. Trying to find more sensitive cheap gauges can be challenging...
 
Hi, thats correct. An air blower feeding to a treatment plant
 

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And here's the duty curve for that unit https://www.nitto-kohki.eu/en/products-en/pumps-a-compressors/air-blowers/item/la-80-b.html

It's only a small unit - you can see that the back pressure range is 1.5-3.5 psi (0.1 - 0.25bar). The red line shows the flow rates at the range of back pressures. You can see it's designed for a duty back pressure of 0.15 bar which gives a flow of 80l/min. If you allow the flow to be significantly restricted the back pressure will increase and the unit will start to run hot. Set a warning marker at say 0.2 bar.

You could also fit a pressure switch that activates at 0.2bar https://www.ebay.co.uk/itm/112015372754 if you wanted to connect a signal/warning
 
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I love a bit of problem solving bodgery so how about teeing in a U tube with a pair of contacts to make a circuit when the level changes past a set limit. Battery and buzzer and away you go.
 
Thanks for the comments and suggestions. As you mention Mr R, I did notice the temperature increase and softening of the flexible outlet hose by chance by just happening to put my hand on the unit as it sounded different to usual . Thought initially it was a pump problem, called out the installer under warranty and it was found the outlet in the plant was partially blocked. I suppose a temperature gauge would also highlight an issue but possibly too late to avoid pump damage. Will search out a dial gauge initially and go from there
 
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