Is the mk25 superior to the mk17???

[CompuDude]

I agree and those are the hoses that take the most abuse. I used to worry about that until I read some very compelling research that use of nitrox mixes reduces hose life by about 40%. Since I often dive florida caves with 30%-32% back gas mixes, I figure that replacing those hoses every few years is just prudent anyway. So any additional stress/wear on the outer casing from excessive bends when the rig is assembled is just an incentive and reminder to replace those as well as the other hoses before the inner section of a hose decides it has had enough.

Or buy Miflex hoses and don't worry about it.

Personally, though, I like the hose routing on the MK25 much better, both for doubles and single tank use.

These seem much cleaner to me:

Compared to this:

That said, my first choice would probably have been the MK19, had ScubaPro not been so moronic about it.

FWIW, I normally dive a drysuit with a standard SPG, so I'm always going to have 4 hoses, except when I'm diving wet. (rare)

 

[Wayward Son]

I hadn't even considered that routing. After looking at this I just moved my 5' hose to the bottom port. Thanks for the tip.

 

[rcpalmer1]

I had my preferred 1st stage crap out after 400 dives so I swapped in a freshly serviced Mk2 from the rental fleet. I know first hand it gets thicker to breathe at 150' off a mk2 piston than a off my usual 'balanced diaphragm.'

Care to explain how at 3300psi starting tank pressures there can be such disparity in inhalation effort?? .

I have been to SP training twice. This was explained to me very well. I will try to relay it as best as I can remember. A mk2 has a flow of about 160cfm and a mk25 has a flow of over 300cfm. This does not matter on the surface. As you go deeper the air becomes more dense. I forget the depth but they said that at deep depths the air becomes thick and flows about like molasses syrup. Also every turn (90deg, normally inside reg)the air makes can cause up to a 15% reduction in flow. This why a high performance reg is needed for deep or working dives. You will never need 300cfm of flow. Even doubles would be empty in seconds, but the air will flow easier.

The MK2 was designed in 1963. It is tried and true. You could probably bury one in muck for a year and it would still work. That is why it is so popular for rental but it is not a high performance reg.

 

[DA Aquamaster]

You're going to be happy with either one, just get the one you want. I second the A700 suggestion, although I have no business doing so seeing as how I've never even seen one. I'm just very curious about how SP's latest retro-project is turning out.

Speaking of which, where's the MK5V or MK10V?

I seen the A700 but have not played with one or took it apart, but I do bench test one.

Personally, I like the G250V in terms of the metal air barrel and the metal orifice - just like the original G250.

I'd love to see a retro Mk 10V since it had a turret, more than adequate flow rate and was smaller and lighter than the current Mk 25.

A retro Mk 5 would offer little over the Mk 25. Oddly though the Mk 25 atached to the A700 has really shiny chrome kinda like a new Mk 5.

 

[DA Aquamaster]

A Mk2 has a flow of about 160cfm and a mk25 has a flow of over 300cfm.

The last numbers I saw for the Mk 2 suggested a 92 SCFM flow rate at a 3000 psi supply pressure.

In the now distant past SP used to publish for their regs in the catalog and piublished numbers at 3000 and 300 psi. The "flow by" Mk 2 and Mk 3 designs are significantly impacted in terms of flow rate as the supply pressure drops. It makes sense as the volume of gas flowing through a given orifice size is directly related to the supply pressure. With an unbalanced design the orifice size is limited compared to the larger orifice possible in a balanced design due to the effects of the uncompensated downstream forces on IP in an unbalanced design.

That drop in IP also means that the reg itself will flow less gas as the Ip drops. With a drop from 145 psi to 120 psi, you'd expect the reg to only flow 80% of what it could do at a full tank pressure.

Even with the balanced MK 5, there was a significant drop in flow at low tank pressures. The Mk 5 and smaller Mk 10 had similar flow at 3000 psi, but the Mk 10 had nearly identical flow at 300 psi, making it a better reg at low pressures than the Mk 5.

 

[Speardoggin]

I hadn't even considered that routing. After looking at this I just moved my 5' hose to the bottom port. Thanks for the tip.

What is the benefit of having a 5' or 7' hose??? I use the regular hose supplied with my MK 25. How is it routed???

Jeff

 

[Wayward Son]

I route a 5' hose under my right arm. The advantage is that in an OOA, my primary is on a 5' hose. My octo is on a bungee on my neck. The extra length on the primary gives us more room to work with & we don't have to be molesting each other to share my gas.