Excellent work. Dave
Good job and on your first attempt as well. That should be a big improvement.
Happy,Try plugging in some different distances to close fully and you will see how much a few thou of extra compression on the springs effects output pressure. Also, take into consideration the force needed to seal at the small end. Once the piston makes contact, the ‘spring rate’ of the sealing material comes into play. As you can see, being a little ‘off’ on measuring can throw your data off. Even the better reg manufacturers have ways to adjust final output. Too many variables. Dave
Sorry, but if Belleville washers are stacked in series (single stack), the force to deflect the washers does NOT increase, only the travel distance needed.... Conversely, if they are in parallel, the force increases but the travel does not.... ) = 54 lbs. for 0.005" .... spring rate = 10800 lbs/in.)( = 54 lbs. for 0.010".... spring rate = (10800 / 2) = 5400 lbs/in.)) = 108 lbs. for 0.005".... spring rate = (10800 x 2) = 21600 lbs/in.Using your numbers, 15 washers stacked up in series )()()()()()()() where it takes 54 lbs. to compress one 0.005" would have a combined spring rate of (10800 / 15) = 720 lbs/in.... If the load on them is 113 lbs. at 850 psi, they should compress (113 / 720) = 0.157".... That works out to (0.157 / 15) = 0.0105" per washer.... If your washers cannot collapse that far, they will go "coil bound" and stop compressing before 850 psi is reached.... If you installed them in pairs, like this.... )) (( )) (( )) (( )) ( .... you would have a situation where the single washer at the right end would collapse fully when the others were compressed half way.... That is why, if I can't use them as singles, I ALWAYS use them all in pairs, with no singles or triples.... So, let's look at 14 washers instead, arranged in 7 pairs.... Each pair would have a spring rate of 21,600 lbs/in.... However, you have 7 pairs, so the spring rate would be (21600 / 7) = 3086 lbs/in.... With a load of 113 lbs. at 850 psi, they should compress (113 / 3086) = 0.037".... That, for sure, would be within the capabilities of the washers to handle without going "flat"....If that stack doesn't work for you because is it too short, you can add more pairs of washers, or you can add flat shims.... In fact, the single washer on the end, in the paired stack of 15, will pretty much act like a shim equal to just over the thickness of the metal in the disc, once it is collapsed.... Let's say that when assembled your setpoint pressure was 500 psi instead of the 850 you want.... From the areas of the piston, we know that there is 113 lbs. available at 850 psi, so that means we would have (500 / 850) x 113 = 66 lbs. available at 500 psi.... The difference is (113 - 66) = 47 lbs.... Since the spring rate of our stack of 7 pairs of Bellevilles is 3086 lbs/in. then you would require a shim of (47 / 3086) = 0.015" in thickness to increase the setpoint from 500 psi to 850 psi.... Each thou of shim will increase the setpoint pressure about 23 psi.... Bellevilles are reasonably linear in operation through the middle of their range.... but even so, these calculations are only an approximation.... Some experimentation will be required to fine tune the setpoint pressure....One other word of caution.... If the Belleville washers collapse flat before the piston seals the inlet side, the regulator will stay "open", and bypass the inlet pressure through to the outlet.... This can happen if you are shimming a regulator, and it can cause you to blow a burst disc, or overpressure the gun, in a heartbeat.... Bob
If I understand this correctly you're having issues with leaks out the vent hole which would suggest a problem with o-rings not a problem with the belleville stack. If the stack had an issue you'd get creep or outright failure of the regulator, a leaking vent hole would be caused by one of the o-rings on either side of the spool. A belleville is a linear spring so if you need 100 lb to flatten is and you preload it to 90 lb then you only need 10 more pounds to flatten it.
A few rough calculations suggest to me that you're reg pressure is around 390 PSI right now. Basically going off the numbers which have been posted previously, 850 PSI = 112lb of pressure on the spool, each washer requires 113lb to flatten completely. Since washers added in series increase the amount of travel for a given applied pressure, we can assume 850 PSI would completely flatten the stack. So if you have 0.1425" total travel in the stack and 0.065" between the seat and spool then 0.065 / 0.1425 = 0.4561 and 0.4561 x 850 PSI = 387 PSI.
If the gauge works (and doesn't leak) but the pressure reading is incorrect, you can calibrate it by popping the lense off (easier said than done), connect it to a known pressure at about midscale and then rotate the scale underneath the needle until it reads correctly.... A tiny drop of glue to hold the scale in place, and then pop the lense back in....Bob
Advertise Here
Share This!