Valve Unseat Pressure Calculator(The Calculator is at the bottom of the page if you want to skip ahead)
Running a lot of boost in your Diesel and want to see if your seat pressure is high enough to control your valve? Want to find out what pressure a valve of given size will start to open at? This tool will help get you started. The math is pretty simple -
Pressure = Force / Area
Pressure = Pressure applied (in our case required to overcome the valve spring)
Force = The force applied to the valve
Area = Exposed surface of the valve
So for a sample if you have these parameters -
Valve Diameter = 1.680"
Stem Diameter = 0.3122"
Spring Pressure = 100 Lbs
The Pressure required to unseat the valve is calculate as follows -
Total Surface Area = Surface Area of the Valve - Surface Area of the Stem
Total Surface Area = (3.1415 * (1.680 / 2.0)) - (3.1415 * (0.322 / 2.0))
Total Surface Area = 2.133
Pressure to Unseat = 100 / 2.122
Pressure to Unseat = 47.125 PSI (the calculator truncates the fraction)
This is often useful in high boost application. Typically in Diesel vehicles where you can create a large amount of boost. It's also useful if you want to make your own blow off valve or waste gate. The value to lift the valve is likely a bit more due to friction in the guide and like a bunch of other forces but this is a general formula to get you started.
Note : units don't really matter can be inches, mm or kPsi as long as its understood if you use Pounds and Inches you will get PSI, Metric is the same idea.