A bell prover is a device that measures a displaced volume of gas at a constant pressure.
What is a bell prover used for?
A bell prover is used to calibrate and verify accuracy of an air flow meter.
Can I see one in action?
Sure thing! In this 20 second video, you can see a process that takes approximately a half an hour in real time. Micah is using the bell prover to calibrate a volumetric flow meter (variable area flow meter).
A one sentence definition is nice, but can I get more info?
Check out this document by NIST (National Institute of Standards and Technology):
Here is an excerpt:
Can I get an air flow meter calibrated for accuracy with a bell prover?3.2.2. Bell Prover
To make a calibration measurement using the bell prover, the meter and its instrumentation are installed and the piping system is tested for leaks. Flow is established through the flowmeter and the bypass valve (fig. 2) is adjusted so that the bell is "floated" off its bottom support. Then the valve is closed so that all the flow is diverted into the bell. Like the piston prover, the bell prover is exercised in this manner in order to attain a steady temperature condition prior to the commencement of the calibration process. The bypass valve is then adjusted to float the bell as before. The valve is closed and following a brief period of acceleration and pressure transients, the bell attains a constant velocity and steady state conditions, and the bell passes through the collection interval. The collection interval for the bell is measured using photodiode optical switches which designate the start and stop positions.
The temperature and pressure of the collected gas upon completion of the collection interval are needed. As for the piston prover, the pressure is measured and averaged over the entire period of the collection interval since the pressure variations due to the prover travel are small and the averaging serves to filter measurement noise. However, the last temperature measurement gathered before the completion of the collection is used. This is because at the highest flows, the temperature variations in the course of a collection are as large as 0.15 K (0.05 %). The collected gas temperature is measured with a sensor inserted into the upper part of the bell, the gas pressure under the bell is measured with an absolute pressure transducer connected to a tap in the inflow pipe (see fig. 2), and the collection is timed with an electronic timer. Details of these measurements and their contribution to the total uncertainty of the system are described in a later section.
We would love to supply you with a flow meter for your application. All of our meters are calibrated and tested before shipment. Air flow meters are calibrated using one of the bell provers in the video above. Liquid flow meters are calibrated using our liquid calibration bench (that's a topic for another time).
Please call us or e-mail us and we'll be happy to help you with selecting the correct meter for your application!
Toll free: 877-356-5463 | sales@flo-corp.com | www.flo-corp.com