ScupaPro Mk10+ IP creep

[halocline]

The older piston design, on the MK5, 10, and 15, had a sharp 'knife' edge that cut into the hard plastic seat and formed a very reliable seal. This is one reason that MK5s are so stable on lock up. At some point (well, with the MK10+) SP decided that they wanted increased flow, so they tried a rounded-edge piston that accomplished two things; better aerodynamics around the piston edge, for increased flow, and supposedly less seat wear because the piston simply sits against the seat instead of cutting into it. However, it took them a few tries to get the piston material and shaping, and I suppose the seat design, to the point where slow IP creep was not a common problem. That's where the latest piston that's on the MK25 really shines.

The irony of this was that the knife edge piston was not lacking in flow in any real-world sense, in fact the MK5 and 10 were considered very high performing regs (still are) but SP has long been trying to bump up the raw flow capacity of their piston regs. The MK25 is touted at 300 SCFM, this is the equivalent of emptying an AL80 in under 15 seconds. Since obviously the tank valve and a couple of high performance 2nd stages have nowhere near this type of capacity, one can only speculate about the practicality of that kind of flow.

 

[oncor23]

"... they told me they lowered the IP..."

I think the only thing they did was to remove a shim. I can understand it from a business point of vue: they did something and collected some money against it; whatever extra they have to do is pure loss. If they had to throw in a new seat, that'd be another extra loss, worth at least $2. Whether or not this is ethical, or even professional, is usually not relevent.

OTOH, I know for sure SP would replace the piston under warranty: a LDS over here confirmed it. But since this can't be a warranty case, and the specs are nearly borderline, your LDS thought they could get away with it. That's sadly common: I have 1 MK20 and 1 MK25 that were freshly serviced before I bought them, and they had a similar case of creep.

It's a definite possibility that all they did was remove a shim. However, the IP creep has decreased, so maybe they put in a new seat, but obviously did not put in a new piston. It's hard to believe they would not question this amount of creep with a new piston and seat. OTOH, they did emphasize that it met factory specs. But factory specs are based on a lockup after 1 minute....right? I believe you are correct...they don't want to put in a new piston and not have the ability to charge for it. So, they did what they did and are hoping it doesn't get worse over the next few months. On my part, I have the capacity and the desire to keep testing if after every dive.

Of course, you are also correct that this is not a warranty case. It then becomes a question for them...what was the creep before they got it, after they returned it to me after service...and what is it now. That would tell the story on who is actually responsible for the creep...IOW, was the creep already high when I turned it in or did it get high after their service. I should have checked the IP & creep and wrote it down before I turned it in. And then checked the IP & creep after I got it back. That doesn't mean they would accept my numbers...but at least I would know.

 

[elan]

Will not increased flow capacity improve the dynamic characteristics? That is faster flow will fill the lp hose faster when the inhale starts thus providing less IP drop?

 

[Zung]

... It then becomes a question for them...what was the creep before they got it, after they returned it to me after service...and what is it now...

That's totally irrelevant.

A good definition of "service" should be some what similar to this: you hand in a piece of gear that's sort of malfunctioning (otherwise you wouldn't bring it back, right?), and they return it in perfect working order in exchange of your money.

Sadly in your case, there seems to be a gross misinterpertation of the term... Or is it because the term has evolved?

 

[elan]

That's totally irrelevant.

A good definition of "service" should be some what similar to this: you hand in a piece of gear that's sort of malfunctioning (otherwise you wouldn't bring it back, right?), and they return it in perfect working order in exchange of your money.

Sadly in your case, there seems to be a gross misinterpertation of the term... Or is it because the term has evolved?

That was one of the reasons I started servicing the regs myself, there is only one tech I would trust and he would always be overloaded, even in off- peak times , most of the others will actually do more harm than good while servicing.

 

[halocline]

Will not increased flow capacity improve the dynamic characteristics? That is faster flow will fill the lp hose faster when the inhale starts thus providing less IP drop?

The idea behind the rounded piston was to improve the aerodynamics so that overall flow would be increased, and I suppose more importantly, more quickly respond to IP demands, resulting in less drop as you mentioned. How much that translates into real-world performance is another story. Don't forget, the 2nd stage and the tank valve both have lower flow capacities than even the MK5. The flow capacity of SP first stages gets measured with a supply that has constant pressure and much higher flow than a scuba tank valve, and is measured with all the LP ports open at once. At least that's what Peter Wolfinger said.

Measuring IP drop with a consumer-level gauge mounted on the end of the LP inflator hose does not work well, as I described in a thread a while back.

I've never been able to tell the difference between the same high performance 2nd stage mounted on a MK5, 10, 15, or 20 with the same IP. Higher IP makes a difference IME, but I still like to set my own regs on the low side. There's plenty of flow and I just tune the 2nds to lower IP.

 

[elan]

Me neither, running apeks scubapro and zeagle 2nd stages on MK5, 20, 25 and zeagle flathead I cannot see the difference. I guess marketing machine just needs fuel to run.

 

[oncor23]

That's totally irrelevant.

A good definition of "service" should be some what similar to this: you hand in a piece of gear that's sort of malfunctioning (otherwise you wouldn't bring it back, right?), and they return it in perfect working order in exchange of your money.

Sadly in your case, there seems to be a gross misinterpertation of the term... Or is it because the term has evolved?

Follow the money. They were willing to look at the regs after I sent them back and "play" with them, because it didn't cost them anything but time. I suppose if they were busy enough, they wouldn't have done much of anything. But replacing the piston and not charging for it? That's money. They might be thinking...darn...we should have replaced the piston if it was creeping too much when we did the last service...but then they have to explain why the piston went bad since it was replaced in the prior service. Of course, I could be wrong about any reluctance. "Whoops, guess your piston is bad. Here's the bill."

 

[elan]

Follow the money. They were willing to look at the regs after I sent them back and "play" with them, because it didn't cost them anything but time. I suppose if they were busy enough, they wouldn't have done much of anything. But replacing the piston and not charging for it? That's money. They might be thinking...darn...we should have replaced the piston if it was creeping too much when we did the last service...but then they have to explain why the piston went bad since it was replaced in the prior service. Of course, I could be wrong about any reluctance. "Whoops, guess your piston is bad. Here's the bill."

I think at least they could communicate that to you.

I spoke to my favorite tech many times and he said that he logs everything, how the reg comes in and how it goes out. All the metrics. So they could have communicate it to you and present you with a choice, even before disassembling the regs if it was having that creep, they could warn you , all it takes is one phone call of the secretary. Even if you have paid for the brand new piston you would have still saved your money because you would not waste your time and that would be even in the case when you were getting a minimum wage.

But I guess we are asking too much

That very tech once would not disassemble the reg before discussing the potential problems with me and getting an OK to go ahead and fix it. It turned out at the end that I did not have to pay anything extra...

 

[oncor23]

I think at least they could communicate that to you.

I spoke to my favorite tech many times and he said that he logs everything, how the reg comes in and how it goes out. All the metrics. So they could have communicate it to you and present you with a choice, even before disassembling the regs if it was having that creep, they could warn you , all it takes is one phone call of the secretary. Even if you have paid for the brand new piston you would have still saved your money because you would not waste your time and that would be even in the case when you were getting a minimum wage.

But I guess we are asking too much

That very tech once would not disassemble the reg before discussing the potential problems with me and getting an OK to go ahead and fix it. It turned out at the end that I did not have to pay anything extra...

Yeah...that sounds really great. I guess techs, and shops, range widely in the information they offer. From the full disclosure model that you report to the need to know version I am experiencing. They don't seem to believe that I need to know what is going on with my regs. I bring them in, they service them...the only input they want from me is whether I like how they breathe. And even then, they may disagree with my choice of breathing ease vs ease of freeflow.