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EHowe
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First Name: Edward
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Locking down HPR Adjusting Nut

Sat Mar 17, 2018 4:04 pm

Recently I opened up My "Hot DAAM" for a routine inspection and found that the nylon adjusting nut on the HPR and backed off from its where it had been set leaving the lever very loose. There was no effect on performance and I imagine that it might on give any advanced warning that the nut/lever was loose until it came off. Which, IMHO would be bad. I replaced the nylon lock nut with a new one I had on hand. I have had good luck using nail polish as a kind of locktite on the original style 2nd stage nuts. Can't hurt to do the same on the lock nuts. Also, I would recommend that the lock nut always be replaced with new if it is removed for any reason.

DerekRalston
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Re: Locking down HPR Adjusting Nut

Sat Mar 17, 2018 7:56 pm

That is VERY odd! I suspect that your nylon lock nut was defective. I've never had a nylock nut move like that, unless it was subjected to severe vibration.

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luis
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Re: Locking down HPR Adjusting Nut

Sat Mar 17, 2018 9:31 pm

Are you sure the nut actually backed off? Did you measure the lever height?
I ask because there is supposed to be play on the lever. The nut should not be tight down against the lever feet.

The true measurement to check the nut is just based on the lever height. When you look at the edge of the can surface, you should see the lever sticking up and see the plastic beads completely, but the lever should not stick up any further. I hope that makes sense.

You can also use the same lever gauge used on a Mistral to give you a reference.

I agree with DerekRalston, I have never seen a nylon locking nut move.


Back in the 90’s I even read a report on a study (I think it was from the Air Force) were they tested the torque value of nylon locking nuts after they have been removed and were being reused. They determined that it was safe to re-use the nuts several times with adequate locking torque. This was even for use in an airborne vibration environment. I can’t remember the maximum number of time they decided was acceptable to use them, but it was more that most of us will consider reusing them. I don't know if they change their service procedures either.

I buy the nylon locking nut in bulk, but still sometimes re-use them in my own regulators if they feel hard to turn. My experience using a torque wrench on nylon locking nuts is that they keep a substantial amount of torque even after they have been reused a few times. But they are cheap so if you feel like replacing them, it is good. YMMV

To be honest, once I adjust the nut in an HPR, there is really very little reason to readjusted. I have just changed the seat when it was too deeply engraved and just put it back together and took it diving. I very rarely with take apart the nut on the second stage, there is no need in most cases.
Luis

Buceador con escafandra autónoma clásica.

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EHowe
Master Diver
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Joined: Sun Aug 28, 2011 2:59 pm
First Name: Edward
Location: Chicago

Re: Locking down HPR Adjusting Nut

Sun Mar 18, 2018 7:33 am

To be honest, once I adjust the nut in an HPR, there is really very little reason to readjusted
I agree. With the nut in question I can easily turn it with my fingers, no wrench needed. This HPR was switched from one reg to another so It was readjusted one time. I had another HPR I bought for my PRAM that hadn't been installed yet so I used the nut from that one and placed the old nut on the uninstalled HPR to hold it together and it has the same issue so it's not a problem with the stem. Nuts are available in the store for $1 I ordered a few to have on hand.

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