For air piping application after the air receiver tank, 2" ss check valves will be installed. I think we are going to select UN3 type from CHECKALL VALVES manufacturer.in the manufacturer datasheets it was shown some values for the spring cracking pressure and standard cracking pressure, the values are .125 , .500 , 1.50 , and 3.50. The pressure rate for UN3 valve is 1500 psi.
Well its surely not cracking at 3.5 times the valve pressure rating, unless its the valve cracking to.
Most spring cracking values refer to the pressure differential at which the valve will start to open.  My guess is that this one refers to a pressure in Barg.  Verify that with the mfgr.
Check valves are designed to crack at small pressures so the flow will be unimpeded in the forward direction, but blocked from flowing backward.  The only advantage to having a higher cracking pressure is that the valve will assuredly be closed when the flow stops and before it can reverse.  If a check valve hangs open until the flow well and truly reverses, then when it DOES close there is very violent water hammer and pieces of the piping system can be dislodged. 

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