Dacor HP seat problem

[Drado]

A few months ago, I purchased Fred Morrison's Dacor Model One double-diaphragm reg (without the dial-a-breath feature). It came with soft and pliable hoses as well, but had no diaphragms:



At any rate, at the time, I made a makeshift diaphragm from my Mistral's old diaphragm, cleaned it up , and it worked well enough to take into the pool:


Bear in mind that at this point of the restoration, I was still using all the original parts (except for the diaphragms of course)

Fast-forward to this week: I was able to acquire some NOS diaphragms to bring my Dacor to a more original state:


Slapped them on and tested them on the bench and they worked fine and actually breathed kinda nicely! Was quite excited to see how they'd perform in the pool, but when the time came, I slapped the reg on to a charged LP72, turned the valve on, and... Nothing! I looked through the exhaust holes in the can and saw that the diaphragm was fully depressed, but still no air. Disassembled the cans (tank valve off, but still under pressure because I was unable to turn the yoke screw) to check the levers, but they were in place, and even manually depressing them produced no air. Apparently it was a 1st stage problem. Got the cans off to expose the pin and tried depressing that as well. It sort of was able to "squish" in, but surprisingly still no depressurization. At this point, I got this feeling that having the pin all exposed like that under pressure and not behaving the way it was supposed to was a bad thing, so I pointed it away toward the pool. Right after doing that, I heard a loud pop and the push pin got shot out into the pool. There was also now this slight hiss as the remaining pressure escaped, but it was a few seconds more before pressure dropped low enough that I was able to unscrew the 1st stage from the tank.

Post mortem revealed a HP seat that looked like this:



Now I don't have any other Dacor seats to compare it to, but I'm assuming that there's supposed to be a metal insert in the middle of the soft seat for the pin to actuate upon? I'm guessing that there was some delamination allowing air to creep along the sides, towards the middle, and out the middle. Does anyone have a photo of an old Dacor seat?

[Bryan]

Should have a metal center...This one is used but you are welcome to it. I can look around for a new one but not likely.

[antique diver]

Drado, you are so lucky that you weren't looking down the bore when that thing came apart!

I think I can help you with a new-old-stock seat for that reg. Take some key measurements of your hp seat so that I can be sure it's the same thing. And don't be looking down any gun barrels either.

[Drado]

Thanks for the generous offers guys. I'll keep them in mind when re-build time comes around.

Regarding the mode of failure though, this one kind of baffles me a bit. A no-air failure is one of those rare events that gives me a moment of pause. From the bench, where it was (subjectively) working fine, to the poolside, where it failed, I can't quite think of a cause. Of course this reg is one where checking for IP creep would be difficult without the proper gauge fitting, so there may have been some trouble before-hand that may have been caught earlier before sudden failure.

Question on the HP seat metal center: Is it an insert, or is it incorporated into the rest of the body of the seat assembly? The reason I'm asking is that its quite possible that if it was an insert, and it did fall out before, I may have overlooked that point during my initial restoration some months back. The reg may have continued to function because there was enough nylon material to interact with the push pin, which eventually wore down (hence the "squish") leading to the no-air failure. The postulated theory above is only valid though if it was an insert. Now, if the part was incorporated into the body, then that's an entirely different story.

[antique diver]

....
Question on the HP seat metal center: Is it an insert, or is it incorporated into the rest of the body of the seat assembly? The reason I'm asking is that its quite possible that if it was an insert, and it did fall out before, I may have overlooked that point during my initial restoration some months back. The reg may have continued to function because there was enough nylon material to interact with the push pin, which eventually wore down (hence the "squish") leading to the no-air failure. The postulated theory above is only valid though if it was an insert. Now, if the part was incorporated into the body, then that's an entirely different story.

The ones I have look like the metal body is all one piece. It may be very thin where it is machined out for the nylon insert, and there may be individual variations in measurements that could let an unusually thin one break from years of pressure from the pin pushing on it. I am hesitant to cut up a new one, but if I can find a used one I can cut it in two and see how it's made.

[Bryan]

I cant speak for the original seats but when the DA, Mistral and Spiro Mistral seats were reproduced the center is part of the seat itself and not put in later. After the seat is formed the seat material is applied while it is very hot and then as it passes thorough the line the excess material is removed from the surface of the seat before it cools. Failure/rejection on seats ran 9% overall.

[Drado]

I am hesitant to cut up a new one, but if I can find a used one I can cut it in two and see how it's made.

Before you do that, I think I'll cut up the one I currently have and see what makes it tick. Will post updated photos soon.

[gj1963]

Topical post as I was just overhauling one last week for a friend. I do believe the center is part of the whole seat. I will be interested in what you find. The one I was working on the seat had been put in upside down - I can only assume to disable the reg as it had sat for many years as a display. I resurfaced the seat it had. Settled in and works but I left it as I would not trust this outside of a pool. I would certainly be interested in a NOS seat if someone has one. The owner of this reg has had it since new and it would be nice to get it to top function. I put a set of USD hoses on it and it was breathing pretty nicely.

Keep us updated on your findings!

[Drado]

Will do Geoff. And thanks for the info about the mushroom valve diameter on the other thread

Right now I'm just debating the best way of dissecting the seat without producing to many extraneous artifacts. I figured if I used a dremel. it would probably melt the nylon and obscure any evidence that could point me in the right directions. Worried though that a hack saw might be too wide and remove any of the finer details. I'll probably end up using the dremel with a lot of cooling fluid.

(BTW, that's a beautiful looking reg you got there! Now if only they performed as nice... )

[1969ivan1]

I will have to double check, but I think I have some NOS Dacor seats in the Scuba Museum's dive locker. I will look for them when I get home as long it does not interfere with the Superbowl.

[antique diver]

I have several of the D1101 Dacor seats, but they all appear to be in an unfinished state... must have gotten shipped in error and no one noticed. See the little off-center tooling bump on the business end. These need to be smoothed off and a dimple made in the exact center of the seat to accept the pin end. I'll try it, but if not successful we might need the help of a more accomplished machinist to make these seats useful. Any suggestions are welcome.

[Herman]

I have a Dacor I need to service and a lathe.....I see a deal working.

Those are pretty bad shape. You will need a 4 jaw chuck and spend a good bit of time on setup.

[antique diver]

I just sent you an email with an idea that may help you, me and the others that might need some D1101 seats.

It involves you working on a few with your professional skills and equipment, and me attempting to make progress with a few of them just because I don't like to give up!

[Drado]

Took some measurements of the seat prior to dissection. Here's a rough sketch with some of the external dimensions:



Bill, do your seats have that 0.09" circular cutout on the sides?



Anyway, did a slightly off-center cut to preserve mid-line detail, and here's what I found:



groove in the middle is where the original center section was I guess, but what's interesting is the size of the space under the nylon seat. If it was produced with melted nylon, then theoretically, that space wouldn't exist, unless something was originally there that got shot out when the seat failed.

Removal of the nylon seat:





I still need to examine the bottom under higher magnification - not sure if there's enough irregularity to the bottom that makes me think that indeed the center was incorporated to the body which eventually broke off. Not quite sure how that could happen, given that the load on it is compressive, and the nylon material should minimize lateral forces that could create shear stress. Ideas?

[Bryan]

groove in the middle is where the original center section was I guess, but what's interesting is the size of the space under the nylon seat. If it was produced with melted nylon, then theoretically, that space wouldn't exist, unless something was originally there that got shot out when the seat failed.
I cannot see how it could have been produced with melted nylon and have this void?

Removal of the nylon seat:




I still need to examine the bottom under higher magnification - not sure if there's enough irregularity to the bottom that makes me think that indeed the center was incorporated to the body which eventually broke off. It looks like the center support was a separate part and not part of the body Not quite sure how that could happen, given that the load on it is compressive, and the nylon material should minimize lateral forces that could create shear stress.
I am thinking the same thing... Ideas?