My lab uses a home-built biomedical instrument that acts as a ventilator for test-subjects. In other words: our device combines nitrogen and oxygen gases and pumps them down the line at a specified rate. The actuation is controlled with three parameters: breath rate (breaths/min), inhalation duration, and breath hold duration. While it is running, it considers these parameters and actuates accordingly.

In order to calibrate our device, we have regulators on each gas line that control their pressures. This obviously changes the gas volume output at the end of the line. What is an easy way for us to measure the volume of gas flow out of the system? I'm trying to avoid buying any devices if I can.


This device is very low output, approximately 0.25 mL/breath or ~40 mL/min. I had originally thought to use a small syringe, but the backpressure was too much for the ventilator.

Our current method for measuring volume output is to fill a bucket with water, place a water-filled graduated cylinder on the surface, and then have the ventilator actuate several times to displace the water in the cylinder, measure that, and then divide by the number of actuations to get volume/breath.

  • $\begingroup$ A calibrated orifice and measure the delta P... but that does mean purchase... $\endgroup$
    – Solar Mike
    Commented Mar 21, 2018 at 19:49
  • $\begingroup$ Would your machine require that there be no back pressure when measuring the output? Also do you have a rough estimate of how much it outputs per minute? $\endgroup$
    – Drew_J
    Commented Mar 22, 2018 at 12:10

2 Answers 2


You can use a float type flowmeter:
enter image description here A float sits in a conically expanding tube, the higher the flow rate the higher the float hovers. In the closest catalog I have at hand, the smallest meter is for flow rates in 0.2 m³/h - 2.5 m³/h range (gas applications).


You can attach the system's outlet to the top of a bucket through a valve on the top.

This bucket at it's bottom and on the other side is connected to an open riser pipe going up just to the top of container to provide a gravity seal. The riser will allow overflow water to discharge.

Then you open the valve for one minute, or the time count of your choice and shut it back.

The volume of water drained out through riser is the volume of output of your system.

If your system generates large volume of gas outlet use more buckets connected on parallel network.


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