Demand valve spring tester

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Open Ocean Diver

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Was having some trouble tuning my SP 108 HP, tuned it best I could, it wasn’t bad but still breathing off it didn’t seem great. It was suggested maybe I have a weak spring and to try shimming it up to increase spring force. I didn’t have any washers that would fit over the poppet stem. So I changed the spring (216) but no difference in tuning. I had a 218 spring so I tried it... Shazam tuned up perfectly. Wasn’t sure what the differences were between the 216 and 218 spring.

Looked online and found the off-road RC car world test and compare their suspension springs to get equal force at each wheel, and they seemed to be similar in size.

After testing the two springs I found the 218 required an increase of 3/4 lbs to compress 1/2 inch compared to the 216.

Does anyone have the specs or know the supposed differences between the two spring are?

Here’s the setup, Dremel tool press and a cheep kitchen scale.

upload_2020-8-1_16-28-37.jpeg
 
I like the idea of a DIY method for testing springs. It would be interesting to see the results from testing a batch of springs, both the .216 and .218.
 
A few years ago I went through a similar painful experience so I decided to test all of my BA/G250 springs-as far as I know they were all -216s. I used a push/pull scale at work and was surprised to find they had so much difference in the total force it took to compress them. I reported my findings to @Luis H who quickly explained I did it all wrong. :-( I don't want to put words into his mouth (hopefully he'll chime in) but is was something like, to do it properly you have to measure the force at a few different points to get the "rate." I.e. force per each unit of length.

Anyway, if you have a known good spring, how about taking the amount of force it requires to compress the spring (after a small pre-load) for example 2mm 4mm 6mm etc. (just throwing numbers out there.)
 
I like the idea of a DIY method for testing springs. It would be interesting to see the results from testing a batch of springs, both the .216 and .218.
Me too, when I get back home next week I’ll test the spares that I have, (4) 216 and (2) 218. Simon mentioned he thought the 218’s were hand-picked for the G250V. (I bought the 218 from him, he’s great to do business with). Will be interesting to see the inconsistencies if any. Although the difference was noticeable in the 108, I’m not sure what the different will do for the single adjustment regulators.
 
A few years ago I went through a similar painful experience so I decided to test all of my BA/G250 springs. I used a push/pull scale at work and was surprised to find they had so much difference in the total force it took to compress them. I reported my findings to @Luis H who quickly explained I did it all wrong. :-( I don't want to put words into his mouth (hopefully he'll chime in) but is was something like, to do it properly you have to measure the force at a few different points to get the "rate." I.e. force per each unit of length.

Anyway, if you have a known good spring, how about taking the amount of force it requires to compress the spring (after a small pre-load) for example 2mm 4mm 6mm etc. (just throwing numbers out there.)
That makes sense, I’ll try that and plot the results when I get home from traveling.
 
Does anyone know the difference between the 216 and the 218 spring and why SP changed the G250V to the 218 in 2008?
 
Here’s some numbers, for what its worth...

Spring compression test:

Spring compression inches, Spring force lbs, spring preloaded.

(218) new... I have two of these one is installed in the 108 which really helped in the 108 tuning. I didn’t test the 218 installed separately, didn’t want to take the 108 apart again maybe I should to compare.

1/16 in 0.9
2/16 in 1.8
3/16 in 2.9
4/16 in 3.8
5/16 in 4.9

(216) original from 108
1/16 in 0.7
2/16 in 1.6
3/16 in 2.6
4/16 in 3.6
5/16 in 4.7

(216) new
1/16 in 1.2
2/16 in 2.1
3/16 in 2.8
4/16 in 3.8
5/16 in 4.9

(216) new
1/16 in 1.2
2/16 in 2.0
3/16 in 2.8
4/16 in 3.7
5/16 in 4.9

Based on the differences in these measurements I’m not sure why the 218 works so much better in the 108. Originally I did try one of the new 216s and didn't see much improvement in tuning.
 
So what is the unloaded spring length, and what is the spring length when istalled (loaded spring length)?
Original 108 = 23mm
218 = 23.5mm
216 = 24mm
216 v 24mm

Wish I knew the installed and loaded length, not sure how to figure that out.
 
Original 108 = 23mm
218 = 23.5mm
216 = 24mm
216 v 24mm

Wish I knew the installed and loaded length, not sure how to figure that out.

Measure depth of orifice while assembled
Disassemble and measure depth of where spring sits in the barrel
Measure length of orifice and seat assembly to where spring sits on the seat assembly
Subtract depth of orifice and length of orifice and seat assembly from depth of where spring sits in the barrel

If I had a 108 I would do this myself. I'm interested in what the force is on a compressed/assembled spring. I'm guessing it's going to be in the range of about 5-10 lbs. so I suspect that you may need to expand your test a little to see what the differences are at the actual working pressure of the spring.
 
https://www.shearwater.com/products/peregrine/

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