Question to Sherwood Brut Specialists

[axxel57]

Hello out there, I got a question to our regulator specialists.
In the last years I got quite some Sherwood Brut Regulators (unbalanced) on my work bench. They are used in salt water all year around in Dive Centers here along the coast.
Since the operators here are not really equipment specialists and their staff is treating the regulators and other equipment like locals treat equipment here, the equipment is usually in remarkable condition when I get it.
Concerning the Brut regs that means that virtually all of them have clogged flow restrictors screws, which means for me that the adaptation of the intermediate pressure in depth is not working. All of those ‘dry chambers’ are partially flooded or show sign s of flooding, but I cannot believe that there can enough water enter from outside through the One Way Bleed Valve to finally increase the IP to its appropriate level.
Quite a while I tried to figure out how dangerous that might be for the customers of those operations. I haven’t heard of any accidents related to this problem, so the divers seem to get more or less enough air to breath.
Most of the dives here take place in depths around 40 to 45 feet, but the so called deep dives are conducted up to about 100 feet.
I know that a reduction of 15-20 psi (the difference between a full tank and a 600psi tank) translates into about 0.4-0.5 inch per water higher cracking effort.
If the 2nds are adjusted to let’s say 1.1 inch of water at full tank, what would be probably the cracking effort at 100 feet?
I translated each 15 psi IP compensation missing in 0.5 inch of water increasing cracking effort, which means at the deep dive at approximately 100 feet the cracking effort could be around 2.6 inch of water at more or less full tank.
If my guess was right that would explain to me why we didn’t have heard of any accident around here yet with those Brut regs.
I just don’t know if I’m right in this linear way of calculating or if there are some other factors contributing to this problem, or if I approached this question anyway from the wrong direction.
Hope my English is good enough to explain what I mean.
Thanks for your thoughts.

 

[Texfrazer]

Hi axxel57!

Can you clarify a little bit?

You stated: "Concerning the Brut regs that means that virtually all of them have clogged flow restrictors screws, which means for me that the adaptation of the intermediate pressure in depth is not working. All of those ‘dry chambers’ are partially flooded or show sign s of flooding, but I cannot believe that there can enough water enter from outside through the One Way Bleed Valve to finally increase the IP to its appropriate level."

Are you asking if water enters the dry chamber in order to affect IP during a dive? If so, the answer is no, Sherwood dry chambers are utilized in the same way as wet chambers in other regs. As someone descends, the dry chamber compensates for depth and maintains a relatively stead IP.

If you are asking about what happens to the IP if the dry chamber floods during a dive, there's only 1 way that can happen, and that is if someone has adjusted the reg to keep air from entering the dry chamber (this is easy to spot under water, as the reg will not be continuously "leaking" the small stream of bubbles from the bleed valve. If the dry chamber does flood, then the IP should continue to remain relatively stable since the dry chamber is now a wet chamber and functioning like the majority of regs from other manufacturers (though the internal parts will be subject to a significantly reduced lifespan due to the contact with salt water).

If you are asking how a dry chamber can flood, that happens when people don't put the dust cover on before rinsing, don't blow out the valve when changing tanks, or (as mentioned above) if the reg is not adjusted properly.

I hope this helps some. Please keep asking questions and I'm sure the friendly folks here will chime in and help out.

P.S. It's been awhile since I actively working on Sherwood regs, so I may have missed something!

 

[axxel57]

What I'm writing about is the fact that those regs have their flow restrictor screw completely clogged, so no air can pass through it and no air is exiting the reg through the one way bleed valve to the outside.
As the name one way bleed valve says, probably no or only very little water can enter the chamber with the main spring.
The hole in the flow restrictor screw is laser drilled, very small and very easy clogged if you don't make sure no water is entering through the filter in the IP chamber, which here around hardly anybody cares about, anyway how often you explain that to the local staff.
If you get water in your 1st stage in normal unbalanced regs with a water chamber for compensating the increasing demand of the IP (intermediate pressure) in depht , it's not nice but is not impairing the basic functions of the 1st stage ( or only when it is very bad).
My question meant to find out what effect in terms of inhalation effort (cracking effort) it has when the adaptation in IP is not happening while going deeper and deeper.
It's the same as if one would close the holes to the water chamber of a let's say a SP Mark II, how much harder would one have to breath with this reg each ten meters (33 feet)?
Hope it's clearer now what I mean......

 

[tfsails]

I've seen water in the air chamber inside Sherwood first stages whose air bleeders did not work. You shouldn't get any water in there, but if the rubber bleeder plug is in the least bit worn, a drop or two could get in there. If the bubbler is not working, the reg cannot sense how deep the diver is and IP will not be adjusted upward as depth increases. Not bad, but certainly not too good. If the bubbler works, then water cannot get inside the first stage because of the pressure differential between the water and the inside of the chamber.

If it's an older first stage, you will probably have to replace the piston. The sintered metal calibrated leak is in the head of the piston. Service techs should know never to put a bleeder Sherwood pistion into the ultrasonic cleaner because the impurities in the cleaning solution will clog the bleeder--instant dead piston!

If is't a newer stage, the bleeder is in the body behind a removable allen screw which has a laser-drilled hole in it. The filter element in this screw is replaceable at servicing. If the bleeder is inoperative, likely you'll have to replace the allen screw, which is right pricey.

I won't turn out a Sherwood with the bubbler inop. I always check them before I take 'em apart so I know whether or not it's my fault the bubbler doesn't work.

 

[axxel57]

Tfsails, thanks for adressing the issue.
These models I'm working on are the ones with the removable restrictor screws and of course everytime they are clogged I'm replacing them( and the filter behind the screw) .
I just wanted to find a way to calculate what it means when the intermediate pressure (IP) is not increasing with the greater depht, because air is not passing through restrictor screw, but on the other hand no water ( or only very little) can enter the chamber because the one way bleeding valve is not supposed to let water into the main spring chamber.
How much is the inhalation effort increasing each 33 feet (10m) and at which depht it is getting dangerous for a diver with such a malfunctioning regulator?
Since I haven't heard of any accident here around with those bad regulators, it seems one can dive also with a first stage that is not adapting the IP to the increasing depht.
Also now I thought that probably a company like Sherwood (PSI) would not get a regulator on the market that so relatively easy can turn into a malfunctioned life support devise.
But what if somebody would try to dive with one of those regs of to let's say 150-180 feet not knowing about the malfunction?
I guess that could be pretty delicate.
I was looking for more arguments, to explain my customers why they always should rinse the regs with the tank air turned on.
Up to now they just have to live with the higher costs of the service, what seems not to bother them too much.
I tried to explain that I consider this neglience as dangerous, but it would be easier to make the point if I could clearly argue that a normal regulator has that and that inhalation resistance on the surface, but the performance is decreasing by that and that number each 33 feet if the restrictor screw is clogged.
Maybe somebody can confirm the calculation in my first post or give me another hint.

 

[diveKi]

I know, this is an old thread, but since the OP is still active in this forum, I think he might be interested in the following discussion on a German google board, which I think might answer his questions of how water could enter the pressure chamber:

https://groups.google.com/g/de.rec.sport.tauchen/c/j7Famjup56g

The discussion is in German, so you need to use a translator tool to read it in English , but I think it should be possible to understand.

 

[buddhasummer]

@Bob DBF

 

[axxel57]

I know, this is an old thread, but since the OP is still active in this forum, I think he might be interested in the following discussion on a German google board, which I think might answer his questions of how water could enter the pressure chamber:

https://groups.google.com/g/de.rec.sport.tauchen/c/j7Famjup56g

The discussion is in German, so you need to use a translator tool to read it in English , but I think it should be possible to understand.

Ja, okay, dank Dir! Ich muss nicht übersetzen....

It's not exactly the issue I was addressing, but interesting anyway.

That the IP adaption to depth doesn't work well when descending fast with CBS System 1sts, is well known.
It takes IP some time to follow up the demand.

Strange only that the 'Tauchen' Magazine claimed that they had proven that this system could fail in extreme dive profiles and that it might have been responsible for the fatal dive of two German Divers in a German fresh water lake.

They wrote they tested later 6 Sherwood regs with a dive to 130feet in cold water with an descent rate of about 60 feet per minute and five of them failed in a manner that the air supply was shut off completely.

I can’t believe that would really happen. That the cracking effort would increase is clear, but no air at all?

Okay, when divers are panicking they have a higher air demand and it might feel to them like not getting air at all.

So I still wouldn't know how to calculate the increasing Cracking effort with increasing depth when the adaption of the 1st stage doesn't work ( with water or air).

But maybe it's not really about cracking effort, but simply about the missing lung volume, which cannot be maintained with the missing IP.

 

[Eric Sedletzky]

The only way I’ve heard of those bleeding regs to get the bubble hole all fouled up is to shut off the air underwater, or forget to open the valve and turn it on underwater. There has to be a lack of pressure inside the reg in order for water to go backwards. Unless maybe people have been sucking tanks dry at depth?
I used to have one of those regs and didn’t like it. I made the mistake if using it as a deco reg where you pressurize the reg then shut it off until you need it. Little did I know that was the wrong thing to do. I switched to Scubapro MK2’s for that.

 

[Bob DBF]

@Bob DBF

It should be resolved by now, as the link is from 1998.

I am confused, as this was not how my Sherwood acted when the dry bleed system malfunctioned and I continued to dive it. To be accurate, there are two different systems, and I believe the one mentioned is newer than mine, however both systems only serve to adjust the IP for depth. If it does not function, the IP will decrease as one gets deeper and the reg, if unbalanced, will breathe harder, I never really noticed in the range of 60', but I learned to dive on some crappy regs so I'm not picky as long as I get air.

If the first no longer functions at all, it sounds like there may be two problems, rather than one.