Sherwood dry bleed contaminated piston

[fmerkel]

This is on a 1990's version. The bleed plug in the piston is hard, very very hard. The diamond bit barely touches it.
If there's a way to replace that bit I'd certainly like to know about it.
If you are talking about the rubber plug on the outside, that appears to be OK, or at least serviceable for now. That's easy to get out and I only used Simple Green on it.

I think you are referring to more modern dry bleed systems. I can't say for sure, since I have not seen or worked with the new system myself. I guess they are replaceable, a reasonable engineering change. Once the piston bleed becomes contaminated it seems to become a throw-away.

 

[abnfrog]

yes if its the newer piston that a permeable bleed (like a 3 micron filter ) is f'ed you need to get a new piston ( I have the replacement part for the piston ) but I only have 1 and I need it , for my regs , bt you do need it to bleed, you can keep the piston for the older regs if you buy one so its not a total loss .....

 

[KeithG]

New approach - I'm taking a small diamond bit in a Dremel to the bleed plug. Take off a little and test it. Getting pretty good at taking the thing apart and assembling again. Last try I got 10cc! Almost up to spec.
I figure, what the hell, got nothing to lose.

Too bad you just can't make a hole the size of a hair. Much simpler, should do the same job. That piston plug is a serious practical weakness, even if a clever engineer concept.

10cc? You are gold! I would stop screwing with it and get on with diving.

The key design principle is to provide "some" positive pressure to keep water from entering the chamber and eventually maybe mucking up the works. the "leak metrics" provided in the service manual are required since standard repair monkeys do not understand how the system works. No bubbles, it is broke. Too many bubbles, it is broke.

You can do a simple test to verify proper operation: Pressurize the reg and leave it in a pail of water for a while (3 or 4 days). Disassemble and check for liquid incursion.

 

[fmerkel]

10cc? You are gold! I would stop screwing with it and get on with diving.

The key design principle is to provide "some" positive pressure to keep water from entering the chamber and eventually maybe mucking up the works. the "leak metrics" provided in the service manual are required since standard repair monkeys do not understand how the system works. No bubbles, it is broke. Too many bubbles, it is broke.

You can do a simple test to verify proper operation: Pressurize the reg and leave it in a pail of water for a while (3 or 4 days). Disassemble and check for liquid incursion.

I would think that it has to have some functional minimum bleed. Too little and you could overcome the what I call 'the static transfer column of air' and back leak water into the reg.
I assume the rubber plug acts as a one-way check valve but I see no good way to check the integrity of that other than maybe your bucket dunk challenge.

 

[KeithG]

I would think that it has to have some functional minimum bleed. Too little and you could overcome the what I call 'the static transfer column of air' and back leak water into the reg.
I assume the rubber plug acts as a one-way check valve but I see no good way to check the integrity of that other than maybe your bucket dunk challenge.

Minimal bleed is "more than zero". We are dealing with a physical hole. As long as the pressure inside the piston is greater than the ambient pressure then air will get forced through.

A simple sanity check is to observe the "stream of bubbles" near the surface and at depth. My buddy's reg presents the same stream of bubbles at the surface as it does at 100 feet (i can't see mine very well).

The rubber plug is a simple one way check valve. It works fine at the surface since our unpressurized regs are soaked in rinse buckets with no issues. We know it is not sufficient by itself at depth since we have seen salt water in the chamber when our LDS screwed up the piston.

 

[abnfrog]

giffenk were you referring to me as a standard repair monkey and I don't understand Sherwood regs ?

 

[KeithG]

giffenk were you referring to me as a standard repair monkey and I don't understand Sherwood regs ?

i am referring to the repair monkeys at both of my LDS who do not understand sherwood regs.

 

[abnfrog]

oh no problem, I (and older instructors ) refer to re and re guys (who don't know how regs work just how to replace parts ) as re+re monkey's ek ek

 

[abnfrog]

ps as your in to I know which shops your referring to ,,,lol

 

[BRT]

Boiling, why didn't I think of boiling.

Yes, it's an old reg, first one my wife bought back in 95'. It starved her for air on an 85' deep dive in current once and was replaced by a ScubaPro MK14....which I use now (she got a deal on a used MK20 from a known source). We converted it to a pony rig, but we're both small, rarely carried the pony so it has mostly just sat for 15+ years. No salt from a tank for sure, and that was before I started overhauling our regs. I wonder now if the reg was messed up way back then.

Been overhauling our main regs and decided to look at that one just in case we did want to use it. Insides were kind of a shock. Not having read through the manual (it's a pretty simple reg to overhaul) and not knowing the cautions about the dry-bleed I just threw the (salt coated) piston the ultrasonic with everything else. I can definitely see some issues with that dry-bleed.

Probably the reason it starved her on air is because the air bleed was clogged. The rubber plug largely stops water from entering the chamber and without the air bleed the reg will not be able to raise IP against ambient pressure so the effective IP drops.