Scubapro MK2+

[AquaNSun]

Hi all, I just got a brand new Scubapro MK2+ from LDS and did a test to find out what
IP range it falls on and to understand its behavior. My test set up was an spg, an IP gauge connected directly to the 1st stage, and a 2nd stage for cycling/purging. To start, I cycled my reg a few times and then let it sat for a minute of two to make sure no creeping and then came back again to check it's final IP after x number of hours.

For those who are interested, my results are as follow:

Tank pressure, IP reading, Test duration, Observation

3000 psi, 135.0 psi, 6 hrs, OK
2250 psi, 132.5 psi, 13 hrs, OK
2000 psi, 132.5 psi, 13 hrs, Final IP = 129 psi, dropped 3.5 psi
1200 psi, 125.0 psi, 3 hrs, OK
1000 psi, 122.5 psi, 12 hrs, Final IP = 120 psi, dropped 2.5 psi
750 psi, 120.0 psi, 5 mins, OK
500 psi, 120.0 psi, 4 hrs, Final IP = 125 psi, creeped 5 psi
250 psi, 118.0 psi, 10 mins, Final IP = 120 psi, creeped 2 psi

Final IP readings were holding and they did not change further.

1. My IP range seems to be between 135psi - 120psi, a 15psi changed from 3000psi to
250psi tank pressure. Is this a typical profile for a new mk2?
On the low side, 120psi, it's out of the recommended IP range, is this still OK?

2. On the few tests where the IP dropped and creeped again, any explanation for
these behaviors and should I be concerned?

3. Looking at the total test hours, about 61 hrs, that is about 60 dives if an actual
diver spends 1 hr underwater and a whole year of diving if the diver dives once
every weekend. At about 47 hrs, when tank pressure was 500psi, the IP started
to show creeping, could this be an indication of the HP seat is getting worn from
long hours of compression? Again, this is just an assumption and could be far from
reality.

My testing wasn't very scientific but I thought it might be interesting to see some numbers. Please feel free to discuss. Thanks.

 

[scubafanatic]

...yeah, I think you've now put enough testing time on the unit you're now due for your first annual.....

 

[halocline]

The IP swing from 135 at 3000 PSI to 120 at 500 PSI is perfectly normal; that's how unbalanced piston 1st stages work. You could put one shim in, which would raise the IP about 5 PSI, then you would be at about 125 with a near empty tank. You actually may notice a slight performance improvement doing this if your 2nd stage is also unbalanced, like the R190 or whatever the current model is. (295, maybe?)

The slight creep at low tank pressure is nothing to be concerned about. Take a few dives with the reg and try again, I'll bet it clears up once the HP seat has taken a more pronounced set. I guess you understand how it works, right? There is a spring holding the the first stage open. When pressurized, air travels through the orifice, then through piston stem into a chamber on the other side of the piston head which forces the piston down against the spring and closes the seat against the orifice. The seat is a nylon (or similar) plug in the end of the piston stem. So when closed, HP air is pushing the seat off the orifice, adding to the force of the spring. IP is the pressure on the other side of the piston pushing back. When there is less tank pressure, there is a need for less pressure to push back to close the valve. That's the drop in IP that you see.

So, even though theoretically the sealing force is the same at all tank pressures, it's possible that at lower tank pressures the seat might not mate exactly with the orifice until it's well broken in, because there are lower forces working on it; that's probably why you're seeing a little creep.

This design of 1st stage has it's performance limitations, but if I were stranded on a fringing reef desert island for a couple of years with nothing but food, beer, and a couple thousand filled tanks, I'd want a MK2 1st stage with a 109 2nd.

 

[herman]

Those reading are about what I would expect. Remember, the MK-2 is an unbalanced first stage so the IP should go down as the tank pressure goes down, about 15 psi is what I would expect from 3000 to 300 psi. Yours is right in line with that. I would not worry about a little creep over multiple hours of setting and don't worry about wearing it out, those little regs are tough.

 

[herman]

.................
This design of 1st stage has it's performance limitations, but if I were stranded on a fringing reef desert island for a couple of years with nothing but food, beer, and a couple thousand filled tanks, I'd want a MK2 1st stage with a 109 2nd.

Amen...although a Sherwood Magnum hooked to the 109 would be perfect.

 

[AquaNSun]

I see. On the HP seat for mk2, is this the same material as the LP seats used in some 2nd stages? For example some DIYers use EPDM 80A-duro to make LP seats. Does it take longer for HP seats to break in than LP seats considering HP seats need to handle higher pressures?

I also attached a cross-section of the mk2 and wonder if anyone has this in English? Out of curiosity, I was looking at the mk2 and Calypso 1st stage which are very similiar except the calypso has an individual orifice piece for the high pressure gas to come from the tank while the mk2 has the orifice built into the body itself and doesn't need to be replaced. Thats another feature mk2 is simple.

 

[herman]

The HP seats are a hard nylon as opposed to the much softer rubber of a LP seat. Making LP seats is easy, HP seats are a little more involved if for no other reason than they are tiny.. Here is the english version of the MK-2 diaghram.

 

[diver 85]

Those reading are about what I would expect. Remember, the MK-2 is an unbalanced first stage so the IP should go down as the tank pressure goes down, about 15 psi is what I would expect from 3000 to 300 psi. Yours is right in line with that. I would not worry about a little creep over multiple hours of setting and don't worry about wearing it out, those little regs are tough.

I love the one I picked up last year--with a R295, put a DR RG1215 octo on, & it's nice little rig....


And I have no idea what the IP is doing, lol.....

 

[DA Aquamaster]

As noted above, the IP change with supply pressure is correct. Personally, I set them up so that the IP is 140-145 psi at about 3000-3300 psi. That ensures it stays at or above 125 psi at 300 psi.

SP limits you to no more than 3 shims, but shims come in 5 and 10 psi flavors so it is not hard to get the IP close to exactly right.

On rare occasions, I will get a Mk 2 that resonates slightly with it set to the proper IP, so in that case, I'll back it down a bit.

 

[AquaNSun]

Herman, what technology was that to convert an identical drawing from xxx to English with such precision! LOL.

It's a lot helful in English now. Thanks.


How do shims work? Is it because adding more shims will compress the spring further and thus making the spring stiffer and requiring higher IP to close the valve?