What is the lifespan of a solenoid?

DeepBlueInnovation

I have a problem with the solenoid on my unit and the question has come up during the investigation process - what is the lifespan of a solenoid? Should it be replaced periodically?

As an aside for anyone interested, the problem I have is that the solenoid has stopped working at depth. When the unit is at the surface it operates as normal firing twice when the unit is switched on, and maintaining 0.7P02 as it should. However in the last couple of dives it started to function only intermittently (max depth 15m), and on the last dive ceased to operate at all after I hit about 6m. The HUD continued to function correctly and was verified by switching the electronics off/on and checking the secondary.

Upon removal of the solenoid, the shell encasing the coil was found to be deeply rusted with rust dust/residue on the plastic taping covering the coil. My suspicion is that as small amount of water has passed the sealing o-ring and this is what has caused the solenoid to cease functioning. Although I found no moisture when disassembling, I believe it is possible that heat from operation has caused this to dry, as it was some 24hours after use that it was opened. After cleaning it will be re-assembled tonight and verified in the next few days.

rdmmdr

new suggestion. if it is broke don't dive it. solenoids don't have a life time, but they do need to be checked for condition at least annually. there is not a dive that is worth your life. if it fails at depth and you can not find out what is wrong, you are the wrong person to be working on the unit. And oc is not that bad after all.

rick

DeepBlueInnovation

Once again Rick, another useless and unhelpful contribution. Try this on for size; if you haven't got anything worthwhile to contribute then stay away from the computer.

If you had the slightest idea of what you are talking about then you would be aware that the Prism can be flown manually, without the electronics. You would also know that the solenoid fails shut, and that if it does blow, it vents into the water. When unable to replicate and identify the cause of a the problem at the surface, I chose to take appropriate bailout and attempt to get a better idea of the problem in a controlled environment.

So, I will make two suggestions with all due respect:

1. If you want to patronise someone - find a good charity and donate generously.
2. Take a long refreshing walk off a short plank.

Cheers,

Ben.

rdmmdr

If the solenoid has not been compromised with water intrusion or water in the o2 side then its life time is almost infinite in this application.

the statement about diving with a broken piece of equipment comes from my aviation background. we are diving with life critical equipment. just because we can get away with it today will not mean that we will get away with tomorrow. Everyone on this board would agree that a pilot that took off with only one engine of a twin engine aircraft is a fool. but we seem to have people repeatedly diving with damaged units.

no dive is worth a life !

rick

cys

I have heard it said that they should be considered for replacement once a year. However, I think their expiration date is a function of how well they are sealed environmentally.

Mdemon

Not on a prism, but when my solenoid failed open on the surface, I dropped a few crystals of citric acid into it and a drop of water. Left it for 30 mins and rinsed. Worked fine afterwards. There's maintenance and there's periodic replacement. I don't know which applies to solenoids. As long as it fails closed, and you are on the ball with your PO2, you can go manual, so only life threatening if your PO2 monitoring sucks.

jradomski

Ben,

I have to agree with rick here... The problem that you describe can easily have the solenoid fail open (A SOLEIND BLOWING APART IS UNLIKELY IN ANY CASE) as easily as it can fail shut.. In this case, unless you have another oxygen source that can be plugged in, flying it manually is difficult at best (by opening and closing the o2 valve).. We all should be able to cope with this within reason, but unless they are going to be weenie dives, diving with a malfunctioning solenoid is stupid..

__________________
Joe Radomski
CCR Trimix Instructor Trainer
ANDI Instructor Trainer Director #10

All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.

DeepBlueInnovation

The prism solenoid is interesting in the way that the gas flow path is reversed, so that if it fails, it fails shut. To be more precise, the 02 flows into the chamber through two large orifices and pressurises the chamber in the solenoid. There is a small central orifice that is sealed by a central spring loaded seat that is drawn down when the current is activated, allowing a small measure of gas to pass through the orifice. So, if the electronics were to fail and the solenoid cease to work, it would fail in the closed position.

The prism has a seperate manual 02 addition line that can be used to maintain the P02. The only situation I can see where gas venting would be an issue is if an 02 line were to blow, and as they are made of stainless steel, this is unlikely.

As I stated earlier, I took separate bailout and undertook a dive in a controlled manner with the specific intent of identifying a problem. It was not a deep dive and it was not in the open ocean. I constantly validated my P02 and the function of my electronics.

So, with a HUD, a secondary that enables me to manually (electronics switched off) validate each cell's reading and adequate bailout, I am yet to be convinced that the process i undertook is any more dangerous than any other dive on a rebreather.

silent running

He he he, you're killing me Ben. Piety is almost always insufferable, despite the obvious good intentions.

silent running

Ben, this is a very good explanation of another great Prism safety feature-all solenoids should fail closed. Thanks for taking the time to explain.

I don't know if you were on Rebreather World 2 years ago, but I posted then about my solenoid clogging up on a trip to Komodo and I had to dive the last 2 days of the trip manually, no big deal. It turned out that I got some wet O2, either during the fills/decanting-which was done on deck in not ideal conditions-or from the supply cylinder itself. The moisture took out/corroded most of the O2 side-reg, piping, solenoid-expensive.

I would guess that a solenoid should last a long time in good conditions. It's not even listed in the Prism maintanence schedule, which goes out to 10 years. But given that you're supposed to replace your lp hoses every 2 and your hp hoses at 5 years and the O2 SS braided lines at 10, I'd say 5 years would make some sense, I got about 4 out of mine before the corrosion/wet O2 problem.

Supposedly the Prism's solenoid can be replaced in the field, but I don't know how it's done. Any solenoid should be easy to replace. I was on a trip where somebody's solenoid failed and due to the electronic's safety features, the unit locked out and couldn't be dived, even manually. It was back to OC for him, boy was he pissed, who wouldn't be?

One thing I've wondered about since is the relationship btw O2 purity and moisture. If you find yourself in a remote location, using an O2 supply that's say 95-97%, it seems probable that the lower % is a result of not vacuuming out the cyl btw fills. And if so, is it that much more likely that excess moisture is also present in the miscellaneous gas that makes up the 5-3% impurity? I know that aviation and medical grades of O2 are supposed to be extra dry. Maybe a higher moisure content is just an unfortunate byproduct of the impurity, which is a problem for us but not for welders, hence the ambush. Make sense? -Andy