Converting kN to Bar: An Explanation and Guide

[josey584]

I have received a pr. gauge for calibration. It's graduations are in bar and kN. The gauge is to be calibrated using kN readings and result should be given along with the uncertainty in measurements. The diameter of the piston used in the system (provided by the customer) is 5.4cm.
Can anybody help me how to read the kN values in terms of pressure? I would highly appreciate if the units are elaborated.

 

[Q_Goest]

Is this for a weight scale of some sort? kN is generally an abbreviation for kiloNewtons which is a unit of force, not pressure. If it's in kN/m², then the conversion is 1 bar = 100 kN/m².

 

[josey584]

Thank you Goest for the comment.

The pressure gauge is used for hydraulic jack.

The outer scale of the gauge is in bar. Inner scales (3 in nos) are graduated in kN with different ranges which can be used with different pistons.
I need to relate the kN values with the piston radius provided by the customer.

Thanks and regards

josey584

 

[Q_Goest]

It sounds like the hydraulic jack is also doubling as a weight scale. That's not unusual, so I'll assume that's what the kN scale is being used for. So the conversion is to simply multiply pressure times piston area. If your piston is 5.4 cm, the area of that piston is 0.00229 m²*. The force produced by the piston is the piston area multiplied by pressure. For example, let's say you have a pressure of 1 bar:

Force = 1 bar * 0.00229 m² * 100 = 0.229 kN

* Note that the area being used is actually the seal diameter which is the cylinder ID if your seals are on the piston which is the more typical case. If the seals are in the cylinder, the piston diameter is the actual diameter you use. I just wanted to point this out because you shouldn't measure the piston to get the area, you should measure the ID of the cylinder.