Venturi Meters
This is a preview of a lesson from course 102 of Fire Pump Academy.
Take this class online and earn continuing education units for your Cal Fire fitter card.
Being able to understand how to test with a flow meter will equip you to be a better fire sprinkler fitter.
Disclaimer:
This eBook and its contents are not a formal interpretation of any codes that pertain to fire pumps. It is the personal opinion of the author and does not necessarily present the official position of NFPA or CalFire or any manufactures mention in this article. Consider this eBook as an asset to help you understand and prioritize your skill set to make yourself a better sprinkler fitter.
For formal interpretations on codes contact NFPA, CalFire or your local AHJ.
Your best resource for fire pump knowledge is your local fire pump representative. Your local fire pump rep knows what pump will work for any given application as well as local codes and the latest industry standards. Don’t forget to tap this resource to make yourself a better-informed fire sprinkler fitter.
Venturi flow meters need a minimum of 5 pipe diameters of straight pipe before and a minimum of 2 pipe diameters of straight pipe after, as well as a way to vent trapped air.

A correctly installed Venturi meter.

An incorrectly installed Venturi meter.
The Venturi meter above is installed incorrectly: wrong sized pipe for the meter and no way to remove trapped air. Venturi meters are shipped with an attached diagram detailing its installation, as well as its calibration certificate. Almost all of the Venturi meters installed incorrectly never have their instructions opened or read by the installed. You will not be able to test a fire pump accurately with an improperly installed Venturi meter.

This Venturi meter is installed correctly. Note it has plenty of straight pipe before and after, plus it has a ball valve on top to vent the air. This installer did it right!
Recording Flow Test Data with a Flow Meter
- Start by replacing the suction and discharge gauges with your calibrated gauges.
- Don’t forget to look for the location of the tachometer and reflective tape and the pump shaft.

- If you can’t find any reflective tape, you will need to add a piece so you can record the fire pump’s rpm.
- Sometimes, you will experience a high rpm reading on a fire pump due to more than one piece of reflective tape on shaft. Make sure there is only one.
- Now, we are running the pump at churn. This is your 0% reading, so record your suction pressure, discharge pressure, and subtract them from each other to get your net pressure.
- At churn, RPMs will be higher than it shows on data plate.
- Remember to record the volts and amps for your 0% data.



- Remember if the fire pump controller doesn’t display volts and amps on a screen, you don’t need to record them. Mark them N/A and note on the report that there is no display.
- Now we begin flowing the water through the meter loop.
- Open the valve that feeds the loop all the way and vent any trapped air by opening the valve on top.
- Use the downstream valve from the meter as your throttle valve, slowly opening it until you see the needed GPM flow on the meter.
- Time to gather the 100% data: record the suction, discharge, net, rpm, volts and amps.




- Now we increase the flow with the throttle valve and take it to 150%.
- Record the 150% data.
- That’s it for the flow test data.
- You will also want to confirm that the casing relief valve is flowing when the fire pump is churning.
- Hit the grease (Zerk) fittings. Check the coupling alignment.
- This coupling was slightly out of alignment and we had to adjust it a bit; we will go into alignment methods a little later in this class.
- If it’s a tank-fed fire pump, you may see the suction gauge go into a negative reading while flowing water. Make sure you add the negative suction pressure to get the net pressure. This should not happen on a flow meter loop test but it’s common on a tank fed test to atmosphere.


To learn more about flow meters or to enroll in course 102, sign up at Fire Pump Academy today.