SCUBAPRO Spring Dimensions

[Six2Life]

Most people that have their G250 or 156 serviced at a shop probably don't realize that for pretty much the same price as the service kit (about $20), which like you said has almost nothing in it; they can get a new poppet with seat and orings, a new spring, and a new balance chamber. The only thing missing would be the 2 air barrel o-rings which probably don't need to be replaced anyways. So if anyone reading this has their reg shop serviced, when you bring it in tell them you want these parts instead of the service kit:

G250 poppet 11.250.015
G250 balance chamber 11.150.102
G250 spring 01.020.216

Also tell them that you want the old parts that were removed returned to you so you can verify that the work was actually done. Then either keep those parts for spares since they are most likely perfectly good (the shop wouldn't have replaced them anyway if you didn't tell them to), or offer them for sale here or on ebay to offset some of your service costs.


I checked the spring that I took out of the G250 again and it turns out it just barely has a flat edge ground on the ends. Definitely not like the new springs where over half the wire diameter is ground away. So probably not a generic spring but maybe not the correct one for a G250???

Also, I pulled out a new 109/G200 spring from my stash and it measured 1.470" in length to throw another data point out there.

 

[redacted]

I doubt if the length of the .216 spring is really a critical parameter. The critical parameter is the force exerted by the spring when installed in its operating envelope so a longer uncompressed spring may exert the same force as a somewhat shorter uncompressed spring base on the material and the number of coils. I would expect the springiness of the material to fluctuate batch to batch. The required operating may have to be adjusted by controlling the length of a coil and the overall length of the spring. This particular spring gets interesting because it has 2 different application; one in the balanced barrel poppet design and the other in the classic downstream design. These two applications require very different forces (one balanced and the other unbalanced) so the operating lengths in each application are quite different. Sure, there may well be some springs gone bad or some that may work better in a balanced barrel poppet while others might be more suited to a classic downstream design. I would think the least forgiving application is in a 108 with a fixed (non-adjustable) orifice where lever height and spring force must both hit the sweet spot at the same nyloc nut adjustment.

So, I would not be too quick to condemn a spring based on a length measurement. I am sure this rational also applies to other springs like those in a 109 or those in a 1st stage.

 

[halocline]

I just think they wear out like anything else. Think about it; they're under compression load all the time, unlike the 1st stage spring. They're going to lose some elasticity over time.

 

[redacted]

I am sure that springs occasionally go bad but I'm not sure they "wear out" as much as they fall victim spec limits coupled with manufacturing and material defects. I suspect they are a lot more like a scuba tanks than an automobile tire. I have some (maybe more than some) pretty old springs in my regulators that all seem to be doing just fine.

 

[Six2Life]

I have heard that the amount and length of time a spring sits compressed has very little to no effect on the spring. It is the number of compression cycles that wears out the spring. I may be completely off base here though.

 

[Zung]

There's vast number of papers on the subject of metal fatigue. This one is almost readable.

The short answer is it'll happen after many millions of cycles, nothing to worry about for breathing thingies. In practice, think of your valve springs that compress 1000's of times per minute and last the life time of your car.

 

[axxel57]

Zung, I haven't read this articel about the spring fatuige yet, willdo when I find time ( thanks a lot).
I'm working everyday on extreme used MKII - R190-R295 and I have to change very often the 2nd stage springs to get the cracking effort in the SP standard range, especially when testing on low tank pressure.
If the IP is okay I check the LP seat, then the orifiice, then the LP seat carrier (stem) if it might be a bit bended and finally I change the spring. That does it mostly, if not I have to check the lever and the washer.
My experience is that the springs in Scuba applications mostly get stiffer with the time and use. Since I get those regs every four to six months on my working bench, I can compare their qualities in my data base.
I don't know why these springs get stiffer and not, as one might suggest, softer with time, but that is what I see quite often.
In average what I see, I have to change the springs after about two and a half years exessive use ( about 1500 dives in sea and pools).
Thanks for reading.

 

[halocline]

I'm not sure that metal fatigue is the whole story regarding spring wear. I just know, from experience, that replacing the spring in G250s/156s et al has improved the reg's performance on occasion. Why exactly that is, who knows.

 

[Six2Life]

Work hardening of the steel maybe??? That might make the spring stiffer with use and also more brittle and prone to breakage?

 

[NotSure]

Work hardening of the steel maybe??? That might make the spring stiffer with use and also more brittle and prone to breakage?

I believe that after many cycles work hardening which is just another name for plastic deformation of the metal should result in a slightly shorter and harder spring. This probably occurs faster in stainless steel because the chromium added for corrosion resistance results in a harder steel with a lower yield strength meaning fewer cycles before plastic deformation occurs.