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The Flowbench is was designed and built at the University of Idaho to measure backpressure caused by mufflers, but can be used to find the pressure through any tube.

UI Flowbench

Using the Flowbench

Plug-In Locations

Because the flowbench uses six motors, the plug configuration is different than a normal outlet. Suitable outlets can be found on the pillars in the senior design suite.

Main Power

The main power for the flowbench is controlled by the uppermost black switch. This provides or cuts power to the other six on/off switches.

On/Off Switches

There is an on/off switch for each of the six individual motors, and motor one can also be controlled by the brass variable control knob on the side of the bench.


The fuse boxes are located directly beside the on/off switches. There is a twenty amp fuse for each motor.

Wire Color

Wire Color is labeled on the fuse boxes: red corresponds to the two front motors, blue corresponds to the middle motors, and green corresponds to the two rear motors. All motors are wired in parallel, and each motor runs to power, ground and neutral.

Air Inlet

The air inlet is labeled and located on top of the flowbench. The plastic and rubber spacers can be used to accommodate different muffler/tube sizes. The inlet must be sealed for the flowbench to be useful.

Mass Flow Sensor

The Toyota Supra mass flow sensor requires a 12 volt power supply and a multi-meter to read the output. The output voltages must be recorded and compared to the calibration data. The easiest way to convert the output voltages to mass flow rates is to use Matlab to perform line regression. To do this enter the voltages and flow rates from calibration and find the equation of the line that is created, then apply that line to the new voltages. A quadratic equation should provide adequate results over the given voltage range.

MAF Calibration Chart

Pressure Sensor

The pressure sensor is battery powered and calibrated to read zero when nothing is blocking the air inlet. The motors can be turned on and pressure drop will still read zero unless tubing is in the inlet. The pressure sensor has multiple built-in options: units, calibration, etc. The pressure drop across the muffler or tubing being tested will be shown on the pressure sensor when the motors are turned on.


If the flow bench is not working, check these first:

  1. Check fuses
  2. Make sure switches have not been overtightened and broken
  3. Make sure the wires in the plug have not come loose