Life span of life jacket gas cylinder

[prv]

It's surely nonsense to use a 40kg scale to weigh a few grams of CO₂. My new cylinders are generally only a gram or two over the stamped tare weight, you do need something fairly accurate to tell the difference between that and a cylinder which is underweight.

The total weight of the cylinder is irrelevant, it's the two or three grams difference between over- and under-weight that matter.

Pete

 

[Amulet]

I'd be willing to bet that cylinders are either empty or full, and that slow punctures are unheard of. However, my safety equipment was all renewed 13 years ago with subsequent refreshment as necessary. 13 year old cylinders weigh correctly and show no significant corrosion. I have had three "in earnest" lifejacket inflations in that period. I service and examine my lifejackets with obsessive care twice annually despite my unnaturally optimistic faith in the technology.

 

[James_Calvert]

On that subject, I've never been satisfied that ordinary kitchen scales are that accurate that they could distinguish between a full and empty 33gm cylinder.

Does anyone have a link to any scales that are known to be that accurate.

I can't remember the actual figures when I did the comparison, but the difference between an empty and full cylinder was very significant, even using spring scales. Try it for yourself!

 

[Mistroma]

I can't remember the actual figures when I did the comparison, but the difference between an empty and full cylinder was very significant, even using spring scales. Try it for yourself!

Cylinder contents vary depending on the device. I think that my old lifejackets are 150N and the cylinder should hold 33gms of carbon dioxide.
This should expand to around 16.8 litres at STP but will be less as it will be under slight pressure when inflated and also rather cold initially.
When related to buoyancy, 16.8 litres converts to around 165N, indicating that my old jacket would get to about 10% above atmospheric pressure if the CO2 managed to warm to 0C.

On the same basis, a 175N device would probably have a cylinder containing about 37.4gm and a figure of 38g CO2 rings a bell. I imagine the CO2 will only contribute around 20% - 25% of the total cylinder weight.

It sounds approx. right and I can't be bothered to check my mental arithmetic just now.

 

[Plevier]

You should unscrew the cylinder and weigh it - you will find a "tare weight" stamped on the side and provided it still weighs at least that (or a couple of grams more) then it's still ok.

No, the tare weight is the empty weight.
The cylinders should weigh that plus the gas weight, normally 33gms or 38gms for lifejackets depending on their buoyancy.

 

[GHA]

Among many choices http://direct.asda.com/george/george-home/salter-electronic-kitchen-scale-white/001460390,default,pd.html?cm_mmc=Shopping%20Engines%20George-_-Google%20Base-_-Baking-_-Salter%20Electronic%20Kitchen%20Scale%20White&istCompanyId=71f4ae42-94c5-4821-aa58-05eff6da2486&istItemId=xlwwmlxqa&istBid=tztx

The resolution is to 1 gm, so if it says test weight +1 gm, you should be happy.

Handy for mixing up small batches of epoxy paint as well :cool

 

[skyflyer]

As an aside

a brillaint (=cheap) source for spares such as cylinders and the little plastic clips, rearming devices etc is these folks

http://www.aspli.com/safety/4/41/52/1/spares-and-accessories

Example (inc VAT)
33g cylinder £7.54
UML trigger £4.79
Compleet pack, cylinder and trigger £11.78

vs Force 4 (as an example)
33g £14.95
Complete kit £15.95

 

[Alpha22]

I just did mine last night..... on a good set of kitchen scales.... all were a gramme or two over the stated weight.
I used a Sharpie marker and wrote the weight and date on the cylinder.....

Interestingly, I replaced all the auto mechs too as they were out of date, one was a good few turns already unscrewed and on its way to falling off. If it had fired it would have been unlikely to have punctured the gas cylinder. That is after one seasons use, as I know I checked them all this time last year!!!!! A warning to us all. It was my jacket too!!!!

Check yours!!!!

As an interesting 'science' experiment me and the daughter filled the kitchen sink and dropped the old auto mechanisms in the sink. They all fired instantly, some were 7 years out of date!! (Ooops!!) but would have worked.

 

[sailorman]

Good for luggage as they have a max. of 40kg. However, the accuracy is only 10 gram and that's not good enough for these small cylinders.

I still have a couple of old crewsaver lifejackets circa. mid. 80s and the cylinders are still fine. I only keep them in case some foreign official insists on lifejackets for a full (but imaginary crew). They haven't been worn for many years but still get an annual check. No problem keeping inflated for a week and cylinders haven't lost any weight. I used to weigh them on laboratory scale but use digital kitchen scales nowadays. Still no sign of weight loss after about 30 years.

 

[Amulet]

The soluble bobbins are essentially fail-safe as far as I can see. If they deteriorate enough they fire the lifejacket rather than sitting there peacefully and then not working.
I check that the gubbins of mine are screwed in properly fairly routinely throughout the season and always if someone hands me a lifejacket on another boat. On one occasion the lifejacket I was handed had no cylinder!
[/U]

I just did mine last night..... on a good set of kitchen scales.... all were a gramme or two over the stated weight.
I used a Sharpie marker and wrote the weight and date on the cylinder.....

Interestingly, I replaced all the auto mechs too as they were out of date, one was a good few turns already unscrewed and on its way to falling off. If it had fired it would have been unlikely to have punctured the gas cylinder. That is after one seasons use, as I know I checked them all this time last year!!!!! A warning to us all. It was my jacket too!!!!

Check yours!!!!

As an interesting 'science' experiment me and the daughter filled the kitchen sink and dropped the old auto mechanisms in the sink. They all fired instantly, some were 7 years out of date!! (Ooops!!) but would have worked.

 

[andygc]

sorry to be pedantic but I recall a lesson in Physics at school pointing out that resolution and accuracy are not the same thing!

Yes, absolutely right, but it's fairly easy to calibrate those kitchen scales. Put a measuring jug on, set the scale to ml or g - doesn't matter which, press the zero button and add water to a known volume in ml. Of course, that assumes you have an accurate measuring jug ...... You can also calibrate them with a joint of beef on the basis that the butcher's scales are checked by Trading Standards.

If you wait until they are in stock at Lidl you can buy the scales and the test weight at the same time.

 

[Mistroma]

Thanks for the picture. The eBay one only displayed 0.01kg. Perhaps your scales are different or the display changes with weight. Could also be that the resolution of the sensor is only to 10gms. No way to tell without more information. However, the one on eBay does say "10 gram / 0.02 pound / 0.5 ounces accuracy". So I personally wouldn't select it as the most suitable scales to check weigh small CO2 cylinders.

I find their claim of 10gram accuracy a bit suspect as that means they would be accurate to 0.025% at 40kgs. That's why I suspected that they meant resolution. However, you may well have more detailed information in the product manual. It does seem like a good price for luggage scales at only £3.58 including delivery.

 

[Mistroma]

As an aside

a brillaint (=cheap) source for spares such as cylinders and the little plastic clips, rearming devices etc is these folks

http://www.aspli.com/safety/4/41/52/1/spares-and-accessories

Example (inc VAT)
33g cylinder £7.54
UML trigger £4.79
Compleet pack, cylinder and trigger £11.78

vs Force 4 (as an example)
33g £14.95
Complete kit £15.95

Many thanks for the link. I was going to have a look for 3 new UML triggers and some lifejacket lights this year and these do look a lot cheaper than buying from a chandler

 

[alan_d]

The soluble bobbins are essentially fail-safe as far as I can see. If they deteriorate enough they fire the lifejacket rather than sitting there peacefully and then not working.

I think you may be being overoptimistic about that. Once when I examined a time-expired bobbin I discovered it was properly screwed in but the soluble bit had degraded so that the firing pin was resting against, but had not punctured, the seal on the cylinder. Presumably the degradation had been so gradual that the firing pin had moved too slowly to be effective.

 

[Mistroma]

I think you may be being overoptimistic about that. Once when I examined a time-expired bobbin I discovered it was properly screwed in but the soluble bit had degraded so that the firing pin was resting against, but had not punctured, the seal on the cylinder. Presumably the degradation had been so gradual that the firing pin had moved too slowly to be effective.

Did it fail to operate when carefully screwed back in place and immersed? I can see it still being held until water was present. Unfortunately, I can also envisage it not being pushed through the seal. It would be good to know the outcome.

 

[alan_d]

Did it fail to operate when carefully screwed back in place and immersed? I can see it still being held until water was present. Unfortunately, I can also envisage it not being pushed through the seal. It would be good to know the outcome.

Didn't try that because:
1. There seemed to be nothing left in the bobbin to dissolve and
2. I had a replacement bobbin to fit to a perfectly serviceable cylinder which I did not want to waste.

 

[Mistroma]

Didn't try that because:
1. There seemed to be nothing left in the bobbin to dissolve and
2. I had a replacement bobbin to fit to a perfectly serviceable cylinder which I did not want to waste.

Makes sense. Later on, I thought that I wouldn't have wasted a cylinder just to try it and so you wouldn't have done it either. I also thought that I should really have asked you if it seemed that the cutter was resting on the seal with nothing holding it back. At the time, it sounded as if it might still have been held back by dry remnants of the soluble material. Thanks for answering that question and it does make a good case for replacing these units.

I have 3 due for renewal and after replacing them I'll keep the old ones lying around and dismantle one each year just out of interest. It's usually very warm and dry when I sail and they are exposed to a minimal amount of spray and rain (lucky me). It will be interesting to see if there are visible signs of deterioration.

 

[nigelmercier]

These look even more accurate. Down to 0.01g resolution up to max 200g. Lifejackets are on board now but anyone know what a full cylinder would weigh?

You need a higher maximum, about 300g. Many available on eBay or Amazon. I've got several for different jobs.