This method describes how to check the Rubber Diaphragm on your Board BS Tester (any make). If the reading falls within 1.6 - 2.1 kg/cm2, then you can continue usage. Else replace the diaphragms to avoid artificially higher results. Presented by PackTest (www.PackTest.com)

1. 1
Diaphragm Calibration
TAPPI T-810 specifies the rubber diaphragm as :
“A molded (disk-shaped) diaphragm requiring a pressure of not less than 160 kPa nor more
than 210 kPa (not less than 23 psi nor more than 30 psi) to distend it to a height of 9.53 mm
(0.375 in.) above the diaphragm plate”
This pressure is also known as the Distension Pressure.
Sr.
No.
Action
1. Remove any sample from the test head.
Rotate the Wheel Clamp clockwise and clamp will move down and sit on the Pressure
Chamber.
2. From between the legs of the tripod clamp, place a pencil (or any light weight article),
such that the pencil sits over the hole in the clamping tripod.
3. Start the machine.
4. Watch the pencil carefully.
As soon the rubber diaphragm swells up and touches the pencil, it will move slightly.
5. Immediately Stop and Reverse the Machine.
6. Record the peak reading.

2. 2
7. Repeat above steps 2 more times and record your Peak readings in the table below :
Diaphragm Calibration Table
Sr. No.
Distension pressure (kPa)
Deviation Remark
Actual Desired
1 160 – 210
2 160 – 210
3 160 – 210
Average 1.60 – 210
If the average of 3 readings falls within the desired Distension pressure or if the
deviation is marginal, you may continue to use the same rubber diaphragm.
If the average is outside the desired range and the deviation is unacceptable, replace
with a fresh diaphragm.