I went down in the basement and took some measurements and made some oil pressure calculations.
The Melling M72HV I have has a pressure regulator plunger with a diameter of 0.622". That's a cross sectional area of 0.304 in2. The pressure relief opening opens when it is depressed 0.42".
The spring that's in the pump has a spring rate of 35 lbs/in so a spring compression of 0.42" corresponds to a spring force of 14.7 lbs.
14.7 lbs spring force divided by area 0.304 in2 means the oil pressure reaches 48 psi before the relief valve opens. Makes sense.
Now. To increase the oil pressure to 75 psi I would need to increase the spring force to 75 x 0.304 = 22.8 lbs.
This corresponds to a spring compression of 22.8/35 inches = 0.65". That's an increase of 0.23" or very close to 6 mm.
So by adding a 6 mm spacer, I should get 75 psi of oil pressure without buying an $8 kit from Summit and paying $11 in shipping.
Or. I could thread the hole and add a screw and a lock nut to get adjustable pressure. But that would be just showing off :lol:
