Mk19 - why so complex?

[jborg]

I service my own gear, and most of it so far is Apeks and Poseidon, with the exception of a couple of G250s. Now I'm blessed with a couple of Mk19/G260 sets, and were looking at the innards of the Mk19 specifically. It strikes me that comparing to an Apeks equivalent first stage (balanced diaphragm with turret), that's a lot of moving parts in there. For example, the Apeks MTX: excluding the port plugs and DIN/yoke assembly (and the decorative bumper that gets removed), I count 22 parts in the actual regulator mechanism, and I understand what each of them does:

Now, the Mk19 has 36 parts in the same path, 60% more than the MTX, and a lot of them are a bit of a mystery to me:

What are the advantages here? One is obvious even to me -- two extra parts constitute the removable orifice, which the Apeks lacks. What about all the other small washers, extra springs, cups, sleeves, discs, etc? Does it make it a better regulator, or just more complex to service?

 

[Mobulai]

I suspect (quite sure actually) this has been covered way better in reg geeks 1 (the thread and the YT video), but I’ll give it a go, and in a word salad format:

• Extra components:
  • removable HP orifice vs an orifice that’s part of the body in Apeks regs, this is a consideration for service, and that’s gonna need it’s own oring
  • 2 in parallel vs 1 IP bias springs, this is the change Scubapro first introduced in the 19>19evo, and later in 11E and 17E2; to make the reg size shorter for the same force (parts 25,26)
  • The DIN retainer style of SP, they use a 2 part retainer, the samller inner part is for direct access to the filter without complete removal of the DIN stem
  • The main HP seat transmitter is a single part for Apeks (#10), but it’s 3 parts that come together to make the same structure (21, 20, 19)
  • The same concept applies to the HP seat (assembly #40)
  • The same for ambient env seal transmitter (assembly 30)
  • Part 24 in tge Apeks is a mixed assembly that has both the balanced chamber and access to the 5th port vs 46 (balanced chamber) and 47(turret bolt and downstream from that all the LP ports); this is a big definitive and unconventional design choice Apeks has to combined functions, but it gives then the option to switch between 4 and 5 LP ports (like the DST)
  • A few extra washers and orings a long the way, it’s a tolerances thing, probably as SP wants to have standard parts that can be doubled up for different size requirements (example #23, the double thrust washers which Apeks don’t even use a single one, as they depend on metal to metal clamping of the main diaphragm— but in various writeups from @rsingler he indicated that this is problematic with champagne bubbles and advised to replace using the thicker scubagaskets 1.6 diaphragm)

Edit: forgot to mention

• The main differences in function:
  • The Balanced chamber assembly thingy (an Apeks special feature)
  • Consequently the “2stage turret levels” in the Apeks (main turret body, 5th port)
  • The diaphragm clamping/sealing mechanism: Friction vs Metal to Metal
  • The env seal transmission balancing (the multi part assembly achieves better transmission ratio)
  • The washers thing mentioned below by @Sebek (body contact im Apeks)

 

[Sebek]

I service my own gear, and most of it so far is Apeks and Poseidon, with the exception of a couple of G250s. Now I'm blessed with a couple of Mk19/G260 sets, and were looking at the innards of the Mk19 specifically. It strikes me that comparing to an Apeks equivalent first stage (balanced diaphragm with turret), that's a lot of moving parts in there. For example, the Apeks MTX: excluding the port plugs and DIN/yoke assembly (and the decorative bumper that gets removed), I count 22 parts in the actual regulator mechanism, and I understand what each of them does:

View attachment 907423

Now, the Mk19 has 36 parts in the same path, 60% more than the MTX, and a lot of them are a bit of a mystery to me:

View attachment 907424

What are the advantages here? One is obvious even to me -- two extra parts constitute the removable orifice, which the Apeks lacks. What about all the other small washers, extra springs, cups, sleeves, discs, etc? Does it make it a better regulator, or just more complex to service?

I think they are very similar in terms of service complexity.

The two extra washers in the HP balance chamber (42/44) make it easier to service than the Apeks. On the Apeks, you have to fish the oring out from the inside of the barrel and it's easy to damage the barrel if you use a metal pick. And it's too small to fit the double hook. I have to use a small plastic or bamboo crocheting hook to get this one out. On SP, the barrel is smooth and the oring is trapped between the washers, it's easy to remove the whole stack.

On Apeks the spring goes directly against the metal back of the seat, on SP there's a lubricating/distributing/centring cup/sleeve. It's not a big deal either way.

The double spring is used to make the reg slightly shorter, also not a big difference for servicing.

 

[jborg]

in reg geeks 1 (the thread and the YT video)

Oh nice, thanks, got my afternoon cut out for me.

 

[Mobulai]

To be fair the larger part count requires higher focus to service (and not forget/misplace something tiny); but it makes removals/centering/adjustments/longevity easier/better so it’s a… preference thing I’d say

 

[davehicks]

I serviced my 3 mk17s (same service kit as mk19) for the first time a few months ago. I have serviced Apeks DS4 & DST many times. I found the mk17 to be really easy to service. It was so clean, the parts all fit and meshed perfectly in a way the Apeks or a Mk25 don't. It really was a joy to service. Honestly, it made me consider getting rid of the rest of my regulators and standardizing on mk17/mk19s.

 

[Mobulai]

I serviced my 3 mk17s (same service kit as mk19) for the first time a few months ago. I have serviced Apeks DS4 & DST many times. I found the mk17 to be really easy to service. It was so clean, the parts all fit and meshed perfectly in a way the Apeks or a Mk25 don't. It really was a joy to service. Honestly, it made me consider getting rid of the rest of my regulators and standardizing on mk17/mk19s.

I’m guessing that the DS4 is for your KISS o2 bottle?

I heard from a friend that TecMe used to make mk17 blanking plugs and springs, and honestly I wanna reach out to Martin and ask him for a few, the mk17 was really nice to deal with opposed to the DS4 env seal that I wanted to replace the WM with (I need an easier source for kits and a m26 option for German diving)

 

[Pearlman]

I found the mk17 to be really easy to service. It was so clean, the parts all fit and meshed perfectly in a way the Apeks or a Mk25 don't. It really was a joy to service.

Perfectly described! I couldn’t agree more! Last year I made my first attempt at servicing scuba regulators and began with the mk25 evo - although it is supposedly simple piston reg, and partly because it was my very first attempt I needed to take it apart and rebuild twice back to back to get the IP just right. A week later I moved on to servicing the mk19 evo and whoa! This is exactly how I felt about it! Don’t let the parts count distract you. Once you create a mental map and memorise the sequence of steps for breakdown and rebuild it’s a breeze!

 

[rsingler]

Great commentary by @Mobulai !
No doubt in my mind that the extra parts contribute to significantly more consistent function in the Mk19 EVO. We could dissect that in even more detail, but suffice it to say, it's well reasoned. Ex: the design of parts 20, 21 & 39 combine to keep the pin perfectly aligned, which is critical to avoiding concentricity and IP leaks.

In contrast, that HP balance chamber in the Apeks, when fitted with a fifth port, it at risk of getting loosened when you change a hose. Unintended consequence of trying to add a feature when it wasn't designed in.

That said, look at the completely different approach that Poseidon took with its magical ball in cup HP seat. Very low parts count.

Only ONE HP o-ring, compared with three HP and one LP in the Mk17!

Elegant simplicity. Smoother HP high speed flow path means less abrasion of 3000 psi components.