Scubapro O-ring Sizes

[redacted]

It would make sense: $7.50 for a genuine SP LP seat (that's what they cost here), $2.95 for an after market replacement. Just like the ink in your printer.

I'm still working on some other sources we may all be able to access. The last time I purchased just Scubapro seats, I paid $2 for the BP LP seat (G250 type) and $6 for a Mk20/25 seat. So I'm thinking $2 would be about right for a generic BP LP seat and $4 for a generic Mk5/10 seat. I'll be calling back on Monday to get cost estimates. This was over a year ago and SP parts prices have gone up since then. I'm thinking even a price match is a good deal given the difficulty we in the USA have getting access to most scuba parts.

 

[Zung]

... $6 for a Mk20/25 seat...

awap, did you re-use the MK20/25 piston stem bushings or is it $6 for the seat and the bushings? I asked in another thread and DA said he thinks they could last maybe 150 dives, and therefore not much more than the stem o-ring.

 

[redacted]

awap, did you re-use the MK20/25 piston stem bushings or is it $6 for the seat and the bushings? I asked in another thread and DA said he thinks they could last maybe 150 dives, and therefore not much more than the stem o-ring.

I'll reuse the bushings. I do have at least one set of extra bushings from past service where I changed the seat and reused the bushings. I guess if I ever have a problem with a leak or extrusion, I'll try switching to a urethane o-ring.

 

[Fox-Cousteau]

I don't know why you're getting so bent out of shape. I asked you nicely to re-check your info on the seats, you told me to "read what you wrote", so I told you that your info was wrong.

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...

 

[redacted]

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...

While it is often difficult to challenge an expert, they too make mistakes. I dug out my stash of SP Mk5/10 seats and, after examining them closely, concluded Mattboy is correct. But if I'm am looking at something incorrectly, I'm ready to be educated. Are you seeing something in the seats differently than I am?

 

[Zung]

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?

 

[redacted]

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?

OK, I got out my brand new el cheap calipers to do some measuring. The -II is obviously higher to the edge of the lip. The + measured 6.8mm to the edge of the lip and the -I measured 7.0mm. But they looki a little different inside the cone. So I went looking for something that would sit inside the cone so the measurement would reflect the depth of the inside of the cone. Well, a nyloc nut (rounded side down) seems to fit in there OK and actually sits just below where the piston edge would sit. Measuring the height including the nut, I got 9.6mm for the + seat and 10.0mm for the -I seat. Did each measurement a second time and got the same result. Then I did the same measurement on the -II seat and got 10.3mm which seems to make sense to me. Finally, I measured a number of IP adjusting shims (washers) and they seem to run about .03mm each.

So I conclude that the + seat requires the most piston travel to seal and will result in the highest IP, the -II seat requires the least piston travel to seal and will produce the lowest IP and the -I is right about in the middle. And each seat change is equivalent to a change of one washer.

Please experts, what am I doing wrong?

 

[Zung]

awap, you're The Man. My mucho cheapo caliper cannot reach inside the cone.

Edit
Now I'm jalous, I'm gonna go buy me that cheapo vernier caliper for 20 bucks!

 

[superstar]

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

 

[Zung]

The other way around, superstar.
Another way of looking at it: seat worn = IP up.
Worn means thinner.