Oil pump piston, some questions.

[Homeoboxter]

Originally Posted by The Radium King

yeah, adding washers (ie compressing the spring) doesn't change the rating of the spring. springs are rated at # / ". ie, it will take 40 lbs of force to compress a 40 #/" spring one inch. it will take another 40 lbs to compress it the next inch. ie, a total 80 lbs to compress two inches.

so, while the washers compressed your spring (and reduced amount of available travel) you didn't change the force required to compress the spring.

The force you need to compress a spring is proportional to the pre-load on it. This means the more the spring is compressed the more force is required for the next increment of compression. This is how motorcycle shocks work when you make it stiffer for the extra weight of the passenger, you just add some pre-load on the spring. So, I think adding a washer pre-loads the valve and it will open at higher pressure.