Sherwood first stage

[nohappy]

I'm reviewing Sherwood's first stage and I found the information is not much. For example, from their website, they mentioned "Two-piece piston for precise optimum balance", but I can't find any explanation how that is going to help precise IP on the internet. Is it because they make a piston stem that has different diameter on each sides (like overbalanced)?
Also, some of the articles mentioned that they have the "dry sealed spring chamber" feature. Is that the same thing as their air bleed system?

 

[JackD342]

I can't tell what you are trying to get at with your questions, but here goes...
Sherwood makes two different 1st stages - the SR2 you linked to in your post, and the 9000 used in all other models. Both currently and historically Sherwoods have been balanced and sealed, rather than exposing the spring chamber to the water.

The balancing is accomplished in different ways. The dry air bleed system is no longer part of the current design. The filter that passed air internally with that design has been replaced with a Schrader valve in the 9000, no longer requiring the constant slow release of air. The SR2 has a different balancing method, transmitting ambient pressure changes mechanically. I think the "precise IP" they are describing for the SR2 is perhaps because the schrader valve in the 9000 could have minor fluctuations as the valve opens and closes, while the SR2 is continuous. Adjusting IP of the SR2 still requires adding or subtracting shims to stay within an acceptable range, and is no more precise than that.

 

[nohappy]

Thank you @JackD342 , that's clear. Do you know what mechanically technique they are using on SR2 so that water do not go in?

I think the "precise IP" they are describing for the SR2 is perhaps because the schrader valve in the 9000 could have minor fluctuations as the valve opens and closes, while the SR2 is continuous

I quote following comment from this article. And from this paragraph, it doesn't look like it is only trying to say SR2 is better than their previous design but to all the products on the market.

The SR2's first stage is one of the only truly balanced first stages on the market today. Most balanced piston regulators come close, but never actually become truly pneumatically balanced. They attempt to, by creating a very sharp knife edge piston sealing surface that cuts into the first stage seat. This cutting of the seat deteriorates the seat rapidly lowering regulator performance over time.

Sherwood addressed this problem and eliminated it! By making a two-piece first stage piston they were able to increase the seating surface sealing diameter without using a knife edge sealing surface. Not only were they able to eliminate the excessive wear associated with knife edge pistons, they were able to create the first truly pneumatically balanced flow-thru-piston first stage regulator. This piston design provides high-flow capacity and rapid response to second stage demand as never experienced in the past.

 

[JackD342]

Well, the mechanical technique to keep water out of the spring chamber is to not drill holes in the chamber...
Design is better than all others? Isn't everyone's design better than their competitors?
The SR2 puts the knife edge on the piston end, not on a separate orifice. The seat is held stationary in a separate retainer. The pressure plate under the dry diaphragm acts on the 3pin link transmitting ambient pressure past the seat to the spring.

 

[lexvil]

Well, the mechanical technique to keep water out of the spring chamber is to not drill holes in the chamber...
Design is better than all others? Isn't everyone's design better than their competitors?
The SR2 puts the knife edge on the piston end, not on a separate orifice. The seat is held stationary in a separate retainer. The pressure plate under the dry diaphragm acts on the 3pin link transmitting ambient pressure past the seat to the spring.

Any chance you have a diagram of the SR2?

 

[nohappy]

@lexvil

I found this on the internet. I can also found its piston stem.

It has different diameter on each end. And that's the question I want to ask, how does that help to achieve better balancing?

 

[lexvil]

Hyperbole is likely the answer to the “better” part, it looks, from the drawing, like a similar composite piston like the SP mk25 at least to me. Looks like a blunt edge piston, to me.
I’m more curious as to the ambient transmitter which looks to be part 15 and it having some sort of dry chamber. I’ve never seem one in person, I would love to see one disassembled.

 

[JackD342]

Yes, part 15 is what transmits the ambient pressure to the spring. I am not familiar with any Scubapro designs, but note part 6 is the seat, and the right end of the piston is the "knife edge."

 

[rsingler]

 

[lexvil]

View attachment 564644 View attachment 564645 View attachment 564646

Still dry bleed?