Vintage or junk?

[Luis H]

delete

 

[Luis H]

I know it’s a great selling point, but I think Fred Roberts in his book, Basic Scuba, made clear that all J-valves are depth-compensating by the nature of the valve.

SeaRat

Fred Roberts made a mistake or more likely he did not explain himself well. He was an engineer, just like I am, and sometime we have been known, to be unable to explain somethings, clearly enough to others.

Fred Roberts was referring that the regulators are depth compensated (and we all know that). Because of that effect, we can draw a bit more air as we are going towards the surface. That is the only depth compenstion that Fred Roberts is talking about, because it was the only depth compensation available when he wrote his book. That effect doesn't matter if you are using a J valve or a K valve. But that is what Fred Roberts was talking about.

The typical J valves are just as much depth compensated as K valves. It is all about the first stages being depth compensated.


The Scubapro DCAR valve has a built in piston that increases the reserve pressure directly. This is completely above and beyond the depth effect that Fred Roberts is talking about.

There is no other valve (that I am aware of) that has this mechanical feature. It is an obvious piston that is open to the ambient pressure and the reserve pressure is obviously influence by this feature. Anyone with any pneumatic or hydraulic experience can examine the valve and tell there is a difference.

This feature is real and it is very obvious. You can say it is a selling point, but that is because no other valve has the same mechanism.


I really hope that this is clear. I have tried to explain the difference before and even do there is an obvious difference (between the DCAR valve and other J valves), maybe I am not been clear...

 

[John C. Ratliff]

Luis,

I’ll look further. Here’s the thread you referred to above.

Scubapro Valve diagram

I have a old Scubapro valve that I use in a Valve Technician class. It is a J-Valve with a built in pressure gauge, and what looks like a screw/valve for adjusting pressure on top. Does anyone know where I can find the exploded parts diagram for this valve?

scubaboard.com

SeaRat

 

[mictrik]

Fred Roberts made a mistake or more likely he did not explain himself well. He was an engineer, just like I am, and sometime we have been known, to be unable to explain somethings, clearly enough to others.

Fred Roberts was referring that the regulators are depth compensated (and we all know that). Because of that effect, we can draw a bit more air as we are going towards the surface. That is the only depth compenstion that Fred Roberts is talking about, because it was the only depth compensation available when he wrote his book. That effect doesn't matter if you are using a J valve or a K valve. But that is what Fred Roberts was talking about.

The typical J valves are just as much depth compensated as K valves. It is all about the first stages being depth compensated.


The Scubapro DCAR valve has a built in piston that increases the reserve pressure directly. This is completely above and beyond the depth effect that Fred Roberts is talking about.

There is no other valve (that I am aware of) that has this mechanical feature. It is an obvious piston that is open to the ambient pressure and the reserve pressure is obviously influence by this feature. Anyone with any pneumatic or hydraulic experience can examine the valve and tell there is a difference.

This feature is real and it is very obvious. You can say it is a selling point, but that is because no other valve has the same mechanism.


I really hope that this is clear. I have tried to explain the difference before and even do there is an obvious difference (between the DCAR valve and other J valves), maybe I am not been clear...

I thought to myself, who is Fred Roberts? Then I looked up "Basic SCUBA" and realized I have that book somewhere. I don' t remember anything from it of course. Bought it back in the 80's. Now when I find it,I am going to see as to what he was referring . I too don't know of any other valve that increases reserve pressure with depth and/or has a selectable reserve pressure. It's a unique valve and of high quality.

 

[John C. Ratliff]

I have been looking, and cannot find the schematic on this valve anywhere. The one in the ScubaBoard link above is not active. In my defense, here in the quote from Fred Roberts in Basic Scuba (page 264):

Constant Reserve "J" Type

...All constant reserve valves are, in effect, depth compensated because of the inherent characteristics of the demand regulator. Because the regulator supplies air at ambient pressure, the spring setting will always be the reserve spring value plus ambient pressure. The resulting pressure will be the cut off point. For examplee, at 100 gfeet th gauge ambient pressure is over 44 psig greater than it is at the surface; thus regulator cut off is about 44 psig higher and reserve will therefore occur at 344 psig rather than 300 psig.

This is why I said that all J-valves are "depth compensated." I always thought that the Scubapro catalog's statement about the "Scubapro D.C./A.R. Valve, Depth Compensated Adjustable Reserve," was more of a marketing statement than a fact. Luis has corrected that, "...The Scubapro DCAR valve has a built in piston that increases the reserve pressure directly. This is completely above and beyond the depth effect that Fred Roberts is talking about..." This is something that none of the catalogs I have seen from Scubapro really explained (I have about four dating back to the 1970s). So these discussions do help explain the mechanics of these valves, and explain from an engineers perspective things that are not generally known. Thank you, Luis!

SeaRat

 

[Luis H]

Take a look at the valve diagram below.

Item 33 is the Poppet and Item 34 is the O-ring on the Poppet.

Item 33 fits inside Item 36 and it seals with the O-ring (Item 34).

Item 36 is the Adjustment Cam Assembly. Item 36 has a small hole on the top which is open to the ambient pressure.

The top portion of the Poppet (Item 33) performs the function of a piston and it seals inside Item 36. The ambient pressure adds a direct force on the top of the Poppet, that is directly additive to the spring force.

You can also see that you can adjust the spring force. You can push down on the Adjustment Cam Assembly (item 36 and turn it 90 degrees so that it catches on the lower position of the Cam Retainer (item 39).

The additional Depth Compensation force is always in addition to the spring force. There is no other valve that I have ever seen (sold in the US or otherwise) that has this feature.

I have seen a diagram showing this, but it might have been a dealer poster that we had. I will look for it some other time.

Again, the depth compensation that Roberts talks about is an effect that has nothing to do with the typical sealed reserve mechanism. You get the same effect with a K valve.