Scubapro O-ring Sizes

[redacted]

thicker seat = more spring pressure = higher IP
thinner seat = less spring pressure = lower IP
shimming spring = higher IP
is this all correct?

You're making my head hurt again.

Shims (on the spring) make more compression on spring and higher IP.

Shims under the seat (so what if it is not in a book) lower the IP because the seat is moved closer to the piston knife edge. This really came from the Mk20 where there was a washer (shim) between the seat retainer and the body that could be removed. As I recall, SP had some issue with the o-ring on the Mk20 HP seat sealing correctly and removing this washer changed the seating surface just a little and corrected the problem. Either that or it was all a dream.

So the thicker seat moves the seat closer to the piston and the piston does not have to travel as far and the spring does not have to compress as much resulting in lower IP.

Thinner seat then give you higher IP.

Where is the vitamin M?

 

[superstar]

stiff spring = higher IP
weak spring = lower IP
shims stiffen spring = higher IP
the closer the seat (thicker seat) is to the piston stem the lower the IP
the farther the seat (thinner seat) is to the piston stem the higher the IP
correct?

 

[redacted]

stiff spring = higher IP
weak spring = lower IP
shims stiffen spring = higher IP
the closer the seat (thicker seat) is to the piston stem the lower the IP
the farther the seat (thinner seat) is to the piston stem the higher the IP
correct?

You've got it.

 

[halocline]

Did it ever occur to you that you might be wrong?
BWD is one of the most respected techs in FL. I'd bet that he services more Scuba pro regs in a week that you do in a year.
you might want to rethink who you are calling condescending...

It did occur to me that I might have been wrong, that's why I asked nicely. I also checked my supply of seats to make sure. I got a little annoyed when I asked this question and was told to "read what I wrote" so I stopped asking nicely and simply stated what was true. I'm sorry if that offends you.

I have great respect for true professionals who do quality work, and I'm always interested in learning more. It is sometimes difficult given the constant barrage of wrong information, misleading statements, and "leave it to the pros" attitude that is so pervasive in the dive gear industry. I'm certainly not accusing Red of any of that, but it does make me a little more sensitive to the perception of being talked down to, even inadvertently.

 

[halocline]

I also took a long hard look at the 3 seats, and I'm confused.

The 1st pic. shows them side by side, -II, -I and +, and the height of the "bodies", the lower cylindrical, part is identical at 6.3mm. The only difference is the upper "lip": the left most one is "-II" and has a lip that appears "whole", while the others seem to have been ground down, and not very precisely at that!

The 2nd pic. is a composite where you can see (disregarding the scale) that no matter what the size of the lip is, the stem always "penetrate" the seat by the same amount. In other words, same height.

What gives? Are we talking about fluid mechanics, Bernouilli & stuff?

The reason that the cylindrical part is the same height in all the seats is because there's a HP o-ring that fits there to keep HP air from leaking out the retainer. If that was different you'd have problems with that seal. Even though your second photo makes it look like the piston would have to travel the same distance to seal in each seat, I don't believe that's the case. If it were, there would be no difference in IP between the different height seats.

 

[halocline]

thicker seat = more spring pressure = higher IP
thinner seat = less spring pressure = lower IP
shimming spring = higher IP
is this all correct?

Nope, the thicker seat actually lowers the spring pressure. The spring does not rest on the seat, it rests between the reg body and the piston head. Shims under the spring result in more compression as you say, but the higher seat means the piston travels less to seal, and so does not compress the spring as much.

 

[Zung]

... I have great respect for true professionals...

And I have great respect for true amateurs because in "amateur" there's "ama" = love, those who do it for love.

 

[Texfrazer]

I'll be calling back on Monday to get cost estimates.

Awap, did you come up with any cost estimates for the seats?

 

[redacted]

Awap, did you come up with any cost estimates for the seats?

I talked to the shop on Tuesday. He made contact with the trident rep who is sending samples an a price list. The shop will test the samples and then we will talk again. This shop very much supports the idea of divers being able to buy parts and DIY. I'm confident he will do what he can for us. It will probably be at least another week before I talk to them again.

 

[Texfrazer]

Awesome!

Though Central TX is a ways from TN, if you're ever in the Knoxville area, dinner is on me!