Question to Sherwood Brut Specialists

[axxel57]

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.

The regs I had been working on with clogged Flow Restriction Screw (FRS) or Sinter Filter (SF) had been clogged mostly because of moisture or water in the tanks and because they had been left for hours in the rinse basin and treated pretty bad.
Even if there should enter some water into the main chamber while diving, a working CBS System should work well as long air flows through the FRS or FS.
It would clog the FRS or SF after the dive when nobody is checking the main chamber, but during the initial dive with some water in the main chamber the performance should be okay.

 

[axxel57]

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.

The 'problem' was finally solved when Sherwood ceased the production of the CBS system in 2009 and brought the new 'Dry Sealed Spring Chamber' System with the Schrader Valve on the market.

Yes, there had been two 'Dry Bleed' systems from Sherwood, the older system with a SF in the piston base (2000 & 3000er series), and later the FRS system ( in the 5000er & 7000er series) with the laser drilled screw in the 1st stage body.

BTW, the IP will not decrease with depth if the CBS System fails, but it will not appropriately increase and cannot secure constant lung volume anymore at depth.

Frankly, I don't trust those tests in the 'Tauchen' Magazine, for me technically it doesn't make sense that the 1st should shut off at about 130' feet (42m) just because it was submerged very fast to that depth.

 

[Bob DBF]

BTW, the IP will not decrease with depth if the CBS System fails, but it will not appropriately increase and cannot secure constant lung volume anymore at depth.

Yeah, worded poorly, the IP should remain about the same, but would seem lower since it is not compensated for depth.

Frankly, I don't trust those tests in the 'Tauchen' Magazine, for me technically it doesn't make sense that the 1st should shut off at about 130' feet (42m) just because it was submerged very fast to that depth.

With an IP of 140# at a depth of 130' the iP would be about 65# lower than an unbalanced reg wants at that depth. I don't know if one could breathe off the reg, but once panic sets in I doubt it. The BC would inflate, but more slowly.

 

[BRT]

Yeah, worded poorly, the IP should remain about the same, but would seem lower since it is not compensated for depth.



With an IP of 140# at a depth of 130' the iP would be about 65# lower than an unbalanced reg wants at that depth. I don't know if one could breathe off the reg, but once panic sets in I doubt it. The BC would inflate, but more slowly.

That little rubber flapper valve doesn't keep water from entering and somewhat adjusting IP. The corrosion this causes will eventually ruin the reg.

 

[Bob DBF]

That little rubber flapper valve doesn't keep water from entering and somewhat adjusting IP. The corrosion this causes will eventually ruin the reg.

That's what happened to mine, except it did not ruin the reg, only the dry bleed system. I had the the dry bleed swapped out, with the last dry bleed the shop could find, and the reg rebuilt. I now use that reg on my pony. Not bad for a demo reg I bought cheap from a shop in 1980.

 

[BRT]

That's what happened to mine, except it did not ruin the reg, only the dry bleed system. I had the the dry bleed swapped out, with the last dry bleed the shop could find, and the reg rebuilt. I now use that reg on my pony. Not bad for a demo reg I bought cheap from a shop in 1980.

The reg floods when the dry bleed stops working.

 

[Bob DBF]

The reg floods when the dry bleed stops working.

Not my experience, although I can see how it could, when unpressurized.

 

[diveKi]

There is another German source in the internet available, which maybe could shed some light on the issue.

It is an openJur document about a case on court. A dive instructor has been sentenced for negligent homicide of a 17 years old diver.

The diver was using an old Sherwood regulator with a malfunctioned CBS, when she went unconscious while ascending.

She was diving for six years. It was figured out, that her regulator became difficult to breathe due to a malfunction in the CBS. This might have led to the situation that she was instinctively holding breath between the breathes.

This caused an expanding lung volume creating pressure on the blood system leading to unconsciousness, resulting in drowning.

URL of the case report:

openJur

I know that Sherwood abandoned the CBS but when looking for a used reg which is cold water compliant I stumbled across several Sherwood regs with the CBS. They receive high praises for being very free flow resistant.

I think, since they are still around, divers should be aware of how to properly use them to prevent any injuries.

 

[BRT]

There is another German source in the internet available, which maybe could shed some light on the issue.

It is an openJur document about a case on court. A dive instructor has been sentenced for negligent homicide of a 17 years old diver.

The diver was using an old Sherwood regulator with a malfunctioned CBS, when she went unconscious while ascending.

She was diving for six years. It was figured out, that her regulator became difficult to breathe due to a malfunction in the CBS. This might have led to the situation that she was instinctively holding breath between the breathes.

This caused an expanding lung volume creating pressure on the blood system leading to unconsciousness, resulting in drowning.

URL of the case report:

openJur

I know that Sherwood abandoned the CBS but when looking for a used reg which is cold water compliant I stumbled across several Sherwood regs with the CBS. They receive high praises for being very free flow resistant.

I think, since they are still around, divers should be aware of how to properly use them to prevent any injuries.

We have been using old Sherwoods for years. Never had them below 150' but they breathe ok with the dry bleed clogged down below 100. They breathe better down there with it working.

 

[rsingler]

It's pretty straightforward to work the numbers.
First, when an uninformed tech gets lube in the piston head filter, flow usually doesn't completely stop, but just slows down. When flow drops from the specified 26ml/min down to say, 6 ml/min (as I've seen many times in eBay regs), the depth compensation doesn't stop. It just slows down.

So let's make some assumptions...
If the volume of the ambient chamber is 5ml, it will take 5/26 minutes, or 12 seconds to double in pressure during descent. That means you'd need to descend from the surface to 33 feet in 12 sec (>150 ft/min) to overcome the ability of the old Sherwoods to keep up.
So if your clogged filter was down to 6 ml/min, descending at 25 ft/min would still be okay.
If you descended at 60 ft/min, your relative IP would begin to lag.

In the worst case scenario, a completely clogged filter with a perfect bleed valve would lose 15psi of relative pressure every 33 feet.
In other words, at 132 feet, the ambient chamber would still be at surface pressure (15 psi), while ambient would be 75 psi.
Thus, your operating IP would be 135-60psi, or 75 psi.

Most balanced second stages will barely register an increase in cracking effort at 100 psi. An old center balanced second like the D400, or my new TFX, won't even notice it. At 75psi IP, cracking effort begins to rise for barrel regs, but not for center balanced valves.

In fact my new TFX, initially tuned to 0.9" cracking effort, will still crack at only 1.4" at 20 psi IP!!!

So with a non-functioning filter, I'd barely notice a problem at max recreational depth.

Of course, there's more to the issue. It's not just cracking effort, but dynamic flow. At 75 psi static IP, there might be a bigger drop in delivered IP during a breath.

But the point is, you're not gonna die due to your tech's excessive lube clogging the filter, even at max recreational depth. And since the bleed valve is never perfect, the reg will flood and the ambient chamber will not stay at surface pressure, but will instead lag just a bit behind actual ambient during descent. So your cracking effort and dynamic IP will be even better.

Yes, you'll have to service your reg for flooding after the dive, but absent unusual circumstances, you'll make it back to the boat alive.

It all depends upon the second stage. In the worst case - an unbalanced second, everything is IP dependent. Here there might be a problem. I measured my old Cyklons in this regard, and they're illustrative.
The Cyklon's cracking effort will rise about 0.2" WC for every 10 psi IP drop. With a Cyklon tuned to 1.0" cracking effort at 160psi IP, cracking effort rises to 2.5" WC by the time IP drops to 100 psi. Attached to a Sherwood with a clogged filter that could be problematic. But balanced seconds are not similarly troubled.