What "expires" on Hammar devices

Roberto

Roberto

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Most Hammar firing devices have an expiry date, usually 5years starting from the time of production; the date is written on the device "replace before end xxxx".

Technically, what "expires" ? I can understand paper activation devices can be sensitive to humidity etc, but a Hammar? Rusting springs, needles?

tia
 
Roberto said:
Most Hammar firing devices have an expiry date, usually 5years starting from the time of production; the date is written on the device "replace before end xxxx".Technically, what "expires" ? I can understand paper activation devices can be sensitive to humidity etc, but a Hammar? Rusting springs, needles? tia
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The salt disc used in some auto ioperate systems is designed to dissolve if immersed and release the spring and plunger but can get damp over time in which case if it disintegrates it operates prematurely. ( An auto self inflated a very old LJ in my locker ), or more dangerously the salt might re-congeal in such a manner as be deposited on spring and plunger and cause corrosion of the steel and failure of spring and plunger. I am not sure what Hammar use but it must be similar.
A marine environment is not good for long term survival of water vulnerable items. Good for sailors though !
 
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I guess, like many things, it's a question of probabilities. As time goes on and entropy takes its toll on everything, the probability of failure increases. There's no actual "failure date" but the manufacturer has to provide one, so a calculation is made (or a guess?) as to when the probability of failure is still reasonably low, but beginning to increase.
 
Good question. There are no salt pills to get moist in Hammar and other hydrostatic mechanisms, but in addition to corrosion of the spring, an issue I can see is mechanical blockage by dust, debris or salt crystals (although those should dissolve again soon when immersed).

I thought perhaps UV damage to the plastic parts (our lifejackets have a clear inspection window over the Hammar unit) might also be a reason, but apparently that's not the case, as the manual units do not have the 5 year replacement requirement.

This illustrative video shows a larger Hammar H20 unit used for liferaft release, but the principle is the same on lifejackets, only instead of a knife there's a needle piercing the CO2 cylinder:

 
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While the potential causes of failure of such items are relatively easy to establish, it is difficult to argue that any are directly related to age. Manufacturers may argue that the probability of failure might rise on older items but suspect if you asked for a justification for this position they would be hard pressed to provide any data. For example will a lifejacket stored in a clean dry warm cupboard perform in the same way after 4 years as one worn daily by a fisherman?

It is no different with items such as the seal on a saildrive or the timing belt on a car engine and it is fear that provides pressure on us to comply, so throwing away perfectly serviceable items. I have 3 cars with Ford engines bought in the same period 2003/4. All have timing belts. I have changed only one (in my Morgan) at 20000 miles and 12 years. It was of course in perfect condition. The one with the highest mileage (a 2l diesel) is still on the original and will stay that way until the car is sold or scrapped.

Manufacturers of "safety" items are able to set replacement periods at a level that indicates a reasonable life by generates good repeat sales. They are helped in this by regulations for some that make such replacement a legal requirement.
 
Do the French authorities not get a little bit twitchy when they find an out-of-date firing mechanism on a lifejacket?
 
Roberto said:
Most Hammar firing devices have an expiry date, usually 5years starting from the time of production; the date is written on the device "replace before end xxxx".

Technically, what "expires" ? I can understand paper activation devices can be sensitive to humidity etc, but a Hammar? Rusting springs, needles?

tia
Click to expand...

I think you will find that inside the device there is still a water sensitive salt tablet, the difference from other units is that the spring loaded valve requires a pressure differential to cause it to open and let in water. As I have discovered they will go off after years of damp living, it is inevitable that eventually enough water gets in to cause the device to activate.

Yoda
 
Roberto said:
Most Hammar firing devices have an expiry date, usually 5years starting from the time of production; the date is written on the device "replace before end xxxx".

Technically, what "expires" ? I can understand paper activation devices can be sensitive to humidity etc, but a Hammar? Rusting springs, needles?

tia
Click to expand...

How about your car air bags, are they ever serviced
 
Tranona said:
While the potential causes of failure of such items are relatively easy to establish, it is difficult to argue that any are directly related to age. Manufacturers may argue that the probability of failure might rise on older items but suspect if you asked for a justification for this position they would be hard pressed to provide any data. For example will a lifejacket stored in a clean dry warm cupboard perform in the same way after 4 years as one worn daily by a fisherman?

It is no different with items such as the seal on a saildrive or the timing belt on a car engine and it is fear that provides pressure on us to comply, so throwing away perfectly serviceable items. I have 3 cars with Ford engines bought in the same period 2003/4. All have timing belts. I have changed only one (in my Morgan) at 20000 miles and 12 years. It was of course in perfect condition. The one with the highest mileage (a 2l diesel) is still on the original and will stay that way until the car is sold or scrapped.

Manufacturers of "safety" items are able to set replacement periods at a level that indicates a reasonable life by generates good repeat sales. They are helped in this by regulations for some that make such replacement a legal requirement.
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Refurbishment itself increases the likelihood of failure; there's the well-known "bathtub curve" that describes the frequency of failures with time after manufacture or refurbishment - the likelihood of failure is high imediately after manufacture or refurbishment, drops to a low "plateau", and then rises as the product reaches either end-of-life or servicing. The question is, is the increased risk of failure caused by servicing or refurbishment greater than the risk of failure from old-age? I would hope that manufacturers would place their recommended service intervals somewhere near the cross-over point between the two. I understand that railway companies abandoned "planned" servicing because of precisely this effect - faults resulting from servicing actually outnumbered failures in service, so it was more effective to simply service things when something broke (obviously, not safety critical things!)
 
yoda said:
I think you will find that inside the device there is still a water sensitive salt tablet, the difference from other units is that the spring loaded valve requires a pressure differential to cause it to open and let in water. As I have discovered they will go off after years of damp living, it is inevitable that eventually enough water gets in to cause the device to activate.

Yoda
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No, the whole point of the Hammar device is that it doesn't rely on a dissolving tablet of some sort. It uses a diaphragm which is deformed by water pressure which it turns releases the spring loaded plunger. See post #5 for the video which is for a raft release device but the life jacket one works on the same principle, albeit at a much shallower depth, and is a work round for stopping life jackets going off because of damp or getting wet from spray.

Interesting article here about airbags which goes some way to explaining why they are lifed to match the expected life of the car. https://www.edmunds.com/car-safety/do-car-airbags-expire.html
 
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duncan99210 said:
No, the whole point of the Hammar device is that it doesn't rely on a dissolving tablet of some sort.
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My understanding is that it does use a dissolving tablet, but water pressure needs to push open a valve before it can reach the tablet. I've seen this stated in writing although it's possible that the authors were misinformed; I can't find an authoritative source either way.

Hammar do have a patent on a device which uses both a pressure-sensing diaphragm and a dissolving part, though the drawings there are not quite the same as their current lifejacket or raft release products.

Pete
 
prv said:
My understanding is that it does use a dissolving tablet, but water pressure needs to push open a valve before it can reach the tablet. I've seen this stated in writing although it's possible that the authors were misinformed; I can't find an authoritative source either way.

Hammar do have a patent on a device which uses both a pressure-sensing diaphragm and a dissolving part, though the drawings there are not quite the same as their current lifejacket or raft release products.

Pete
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No mention of any dissolving parts here in Hammar's own blurb about their inflator. It's all on the 10cm depth required to trigger the hydrostatic valve.
 
duncan99210 said:
It's all on the 10cm depth required to trigger the hydrostatic valve.
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That's because that's simultaneously the benefit of their product and the part that surprises people (when they lie on their backs in the sea and it doesn't go off) :)

Some of their blurbs do mention sensing both pressure and water; if it were purely a diaphragm as drawn in the video then it wouldn't be sensitive to water and would go off with a 0.01bar increase in air pressure alone.

I don't know what the real answer is; to a large extent it doesn't really matter to us as users. I am curious, though. Unfortunately I don't have any expired ones floating around to cut into, but if I remember I might do so at the end of the season when I have a couple of jackets needing renewal.

Pete
 
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I've no knowledge of Hammar kit, but I serviced an elderly friend's lifejackets a few years ago and the activators were 7 years out of date, but went off with a satisfying pop when immersed.

[cynic] I suspect that expiry dates are a tussle between the accountants who want a short date to sell more replacements and the new sales marketing people who'd like to boast of a long life. There may also be a bit of input from the engineers who actually understand the product [/cynic]
 
duncan99210 said:
No, the whole point of the Hammar device is that it doesn't rely on a dissolving tablet of some sort. It uses a diaphragm which is deformed by water pressure which it turns releases the spring loaded plunger. See post #5 for the video which is for a raft release device but the life jacket one works on the same principle, albeit at a much shallower depth, and is a work round for stopping life jackets going off because of damp or getting wet from spray.

Interesting article here about airbags which goes some way to explaining why they are lifed to match the expected life of the car. https://www.edmunds.com/car-safety/do-car-airbags-expire.html
Click to expand...

Maybe the latest ones don't but the ones I have had to change definitely had a dissolving part inside protected by the spring loaded valve that is obviously pressure sensitive. The link below is worth watching.

https://www.cmhammar.com/products/p...ator/out-of-water-performance/#prettyPhoto/0/

Yoda
 
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