Air Gun Home :: View topic

rsterne · Moderator

I've been trying to figure out how to adjust HPA regulators.... and after pumping to the point of getting VERY tired of pumping with very confusing results.... I made up a spreadsheet to try and figure out WTF was going on.... Once I did, I quickly realized that mixed stacks of washers (ie some singles, some doubles) are very difficult to adjust.... Shocked

.... Let me backtrack a minute....

Belleville washers are cupped washers (AFAIK Disc Springs work in virtually the same way) that produce a force when compressed, just like a spring.... Compared to a typical spring, however, they have a very high spring rate (ie are very stiff) and very little travel.... As an example, a washer similar to that found in a JDS Airman regulator (but not as stiff) has the following specifications:

Outside Diameter - 0.62"
Inside Diameter - 0.32"
Thickness (of the material) - 0.022"
Cup (available travel) - 0.020"
Unloaded Height - 0.042"
Force to Flatten - 100 lbs.
Spring Rate - 100 / 0.020" = 5,000 lbs./inch of compression

If you stack two washers in the same direction.... ie (( .... you get the same travel (0.020"), but double the spring rate (10,000 lb/in)....
If you stack two washers in opposite directions.... ie () .... you get double the travel (0.040"), but half the spring rate (2,500 lb/in)....
If you stack four washers in two pairs.... ie (( )) .... you get double the travel (0.040") and you are back to the original spring rate (5,000 lb/in)....
If you now stack 8 washers in two sets of four as above.... ie (( )) (( )) .... you now have four times the travel (0.080"), but half the original spring rate (2,500 lb/in)....
Note, stacking the washers )) (( )) (( is the same as (( )) (( )) in terms of rate and travel but is usually provides better contact with the spring seats (especially in a regulator, where one seat has a hole in it for the piston to pass through)....

If you need more length you can use 12 washers arranged )) (( )) (( )) (( .... You would get 6 times the travel (0.120") and one-third the spring rate (1667 lb/in)....
Need a stiffer spring?.... 12 washers arranged ))) ((( ))) ((( would give you only 4 times the travel (0.080") but the spring rate is now three-quarters of the original (3750 lb/in)....

By now you are beginning to understand that there are a huge number of combinations that would produce various lengths and spring rates.... Let me simplify it for you....

DON'T MIX SINGLE AND DOUBLE STACKS (OR DOUBLE AND TRIPLE STACKS)....

What will happen is that if the force you need is more than the flat force of a single washer, that washer will be flat as if it's a shim.... Same for a double stack.... If the force you need is greater than what it takes to flatten a pair of washers, that pair will go flat.... The only reason to mix types of stacks is if you want a "progressive" spring rate.... ie where the spring is softer initially, and then the rate increases once the thinner stacks collapse fully.... I have found that some belleville washers, once collapsed "flat" may not return to their original "cup".... making further adjustments difficult if not impossible....

Some regulators I have had apart had a mixture of single and double stacks, plus possibly a shim.... for instance, 13 washers arranged ) (( )) ( ) (( )) (( .... I see absolutely no reason for doing this (other than cost).... A far simpler approach would be to use 12 washers in pairs, plus a shim.... )) (( )) (( )) (( | .... Not only is it easier to understand, but it reacts in a sensible, understandable manner to increases in the thickness of the shim, which cannot be said for a mixture of single and double stacks.... Rolling Eyes

I hope that helps you understand a bit about how belleville washers (disc springs) work.... Wink

Bob

Alstone · Moderator & Site Supporter

Brilliant!! piece of work Bob. Thumb Up!

I haven’t seen a better explanation of the use of Belleville washers, and their not the easiest things reset if you don’t know what your doing. Smile

I’ll copy and save this one. Cool

Al