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Controlling air

Monitoring and controlling flow and pressure

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Vagulus10/10/2020 00:11:34
5 forum posts

My project is driven by low pressure air (about 0.5 Bar). In fact its supply is from an air pump rather than a compressor.

Does anyone know where I can obtain a flow meter (0 - 30 l/min) and a relief valve which will operate at that pressure?


I.M. OUTAHERE10/10/2020 07:31:53
1468 forum posts
3 photos

Would 0-30l/m possibly fall into the flow meter range for a tig welder flow meter ?

0.5bar or 7.5psi relief valve , maybe something off an airbrush unit ?

Just a few thoughts .

Vagulus10/10/2020 07:46:22
5 forum posts

Does XD 351 hint at another Australian?

Good thinking. I actually tried a TIG flow meter but they require minimum OP of 0.35 MPa (3.5 Bar) and I want to work below that. I'll try my art supply shop. They should know something about airbrushing.


I.M. OUTAHERE10/10/2020 08:14:58
1468 forum posts
3 photos

Yep Aussie !

Also look at Medical stuff - just a thought .

What is your project ?

Understanding what you are trying to achieve will help the forum members to help you ,

Vagulus10/10/2020 08:47:44
5 forum posts

I can't really tell you what the beasty I am prototyping is or does. All I can say is that the air has to blow bubbles at the bottom of a water tank one metre deep. That actually means an operating pressure of 0.1 Bar. I have been saying 0.5 Bar to be on the safe side. wink

I.M. OUTAHERE10/10/2020 09:07:51
1468 forum posts
3 photos

If you are playing with water then try places that deal in fish tanks or aquariums , also look at scuba diving gear .

Vagulus10/10/2020 09:09:09
5 forum posts

More good thinking.


DMB10/10/2020 09:12:00
1062 forum posts


XD351 beat me to it, i was going to suggest an aquarium aerator. If it blows too much air, excess could be bled off via a pipe with some sort of relief valve. Dont know exactly how they work.


Clive Steer10/10/2020 10:20:11
32 forum posts

You may consider using a positive displacement pump of known swept volume and controlling its speed to provide the flow rate needed and the pressure will sort itself out determined by the head of fluid in the tank.


Vagulus10/10/2020 23:13:15
5 forum posts

My thanks to all of you. Your input has crystalised my thinking - and I have been barking up the wrong tree. angry

I have been confusing where I am now (at the experimental stage) with where I want to be (the testing stage). I should be able to use the TIG flow valve to measure the flow needed to make the thing work. Then I can get into designing the double-acting bellows pump I have in mind to give me the right amount of air. Clive is right - I'll let the pressure sort itself out.

I think I know where I am going now. wink 2

Much appreciated.

Paul Lousick11/10/2020 00:51:28
1688 forum posts
624 photos

Try a paint spray gun supplier.  Advertised air pressure regulators state an output pressure range from zero psi


Edited By Paul Lousick on 11/10/2020 00:53:10

Alan Charleston11/10/2020 06:06:04
104 forum posts
20 photos


I used to do the same as what you are planning to do when I worked in a factory. I hooked a pressure sensor to a tee on the air line and connected it to a data logger to measure the height of water in a tank. I originally tried to control the rate of bubble formation using a pressure reducing valve. The problem was that the flow rate varied with the depth of the liquid and I could never get a stable air flow rate.

I ended up using plant air at 110 psi through a ball valve.

Get the smallest ball valve you can find, shut it and connect between an air compressor and your tube. Put the tube into the liquid and slowly crack the ball valve open until you get the desired flow rate (bubbles/second). If the liquid level changes it shouldn't affect the flow rate as the supply pressure is so much greater than the variation in back pressure and the pressure drop change across the valve ( and hence the air flow rate) will be trivial. If you want to monitor the liquid level then put a tee in between the valve and the tube and connect it to a pressure gauge.

Trying to get a stable air flow by setting the pressure will not give stable operation.



Neil Wyatt11/10/2020 16:29:59
18485 forum posts
719 photos
78 articles

For large flows at low pressure a simple flap in a box gauge will work well, the closer to balanced you weight it the more sensitive it will be.

Someone with arduino expertise may also be able to hack a car mass flow sensor.

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