Freeflow MK25 s550

[DA Aquamaster]

DA, a question. I assume my mk15 has the spec system and has been packed with Christolube, if I remember from an earlier post of yours. I actually might be in some pretty cold water this summer if I can make it out to Clear Lake in Oregon, right near where my sister lives.

Unfortunately no. The SPEC boot is the limiting factor here. (There is also a liability factor for the shop in doing something that is no longer SP approved. I use SPEC boots on my own regs but then I am not likely to sue myself for doing something that is no longer factory approved.)

The first Mk 3's, Mk 5's and Mk 10's designed to use a SPEC system had really small holes in the ambient chamber (maybe 1/16" in diameter) that made it more difficult for the silicone to leak out. But they still none the less added a boot a few years later to keep it in better. The Mk 15 however was designed from the start to use a SPEC boot and had much larger holes in the ambient chamber. So unless the boot is in place, the silicone departs very quickly. These holes incidently got even larger and more oval in shape on the Mk 25 to improve water flow in and out of the ambient chamber so it is even less an option on anything other than the earliest Mk 25's.

The bad news is that SP has been recommending that techs remove SPEC boots on Mk 15's and Mk 20's (as well as Mk 10's) and then not fill the chambers with silicone and instead just coat the parts inside the ambient chamber with Christolube for antifreeze protection. So nearly all the Mk 15 and Mk 20 SPEC boots have been thrown away over the years since SP went to the TIS system during MK 20 production and now does not stock replacements.

The semi-good news however is that Mk 15 also introduced a piston bushing to help insulate the head of the piston as well as a teflon coated mainspring so it is mostly TIS equipped already. Unless you are going to be in water colder than 45-50 degrees, it would not be something to worry about.

I recently bought a very nice Mk 15 first stage that is missing the SPEC boot. Since I like the SPEC system but cannot find a SPEC boot, I cut a small piece of bicycle innertube to serve as a surrogate spec boot and will see how well this works at retaining the silicone in the ambient chamber. It is again not SP approved but would be a possible option for do it your selfers.

I also assume the metal case balanced adjustable 2nd stage would be better suited for really cold water than a modern plastic 2nd stage, correct.

The metal case and metal air barrel allows exceptional heat transfer and I have never had a metal cased second stage freeze up or spit chunks of ice at me. They are also very nice to use in terms of dry mouth as the metal causes moisture from your exhaled air to condense on the air barrel which is then re-inspired on the next breath so dry mouth is a very rare occurrence.

Your G250 is also one of the older ones with a metal air barrel. This allows heat to flow to the air barrel from the metal inlet fittimg outside the second stage and also from the metal adjustment knob on the other end of the air barrel so they also do very well in cold water. The metal air barrel also makes them relatively dry mouth free like the balanced adjustable.

 

[trevinkorea]

Thanks for the great advice.

When the LDS told me it was impossible, I purchased the hoses and did exactly what you suggested. (didn't use tape, used a rag instead - no damage)

I pool dove the reg and it couldn't supply enough air. It fluttered a lot in the diaphram (second stage) and just did put out at only 5 metres. If I was completely still, and breathing extremely lightly, it would almost deliver enough to be comfortable.

Could you suggest why this happened and how I could fix it. The LDS refuses to turn up the IP, also claiming that it would result in freeflow so, I'm on my own with this one.

Also, the regs were recently serviced. (same LDS - not sure about the service as he did not return the used parts as requested.)

Thank you again.

 

[DA Aquamaster]

Did it do this with the short hose or is this just occuring with the long hose? It's possible there could be some type of resonant effect occurring that is causing the piston in the first stage to flutter a bit but it would be the first time I have encountered this phenomenon and would suspect something else may be wrong.

If there is some resonance occurring changing the IP should resolve the problem as it would also slightly alter the working range of the piston. I have found that Mk 3's and Mk 2's will often whistle due to resonance unless there is at least one shim installed. I suspect this effect could be magnified with a long hose.

Do you know what the IP is for the reg at 3000 psi? The Mk 2 needs to be set as close to 145 psi as possible on a full tank as it will drop approx 20 psi as the tank pressure falls to 500 psi. So if you do not start out at 145 psi the IP falls below the normal range before you reach the end of the dive. In the Mk 2 the IP is set by adding shims under and over the mainspring.

 

[trevinkorea]

The flutter and volume problem is just with the reg on the long hose.

I'm not sure what the IP is set at but it was just serviced to spec for the mk20. ( I use a MK 20 not a Mk 2.

THe regular stock primary hose does not experience this problem and I've checked the 7ft hose and there are no blockages in it. I suspected this could be the problem but it was not.

The short hose also has no problems with breathability, just the long hose reg.

Thanks again. It's awesome to be able to pick the brain of someone with so much knowledge.

Trevor

Did it do this with the short hose or is this just occuring with the long hose? It's possible there could be some type of resonant effect occurring that is causing the piston in the first stage to flutter a bit but it would be the first time I have encountered this phenomenon and would suspect something else may be wrong.

If there is some resonance occurring changing the IP should resolve the problem as it would also slightly alter the working range of the piston. I have found that Mk 3's and Mk 2's will often whistle due to resonance unless there is at least one shim installed. I suspect this effect could be magnified with a long hose.

Do you know what the IP is for the reg at 3000 psi? The Mk 2 needs to be set as close to 145 psi as possible on a full tank as it will drop approx 20 psi as the tank pressure falls to 500 psi. So if you do not start out at 145 psi the IP falls below the normal range before you reach the end of the dive. In the Mk 2 the IP is set by adding shims under and over the mainspring.

 

[DA Aquamaster]

Sorry...I'm not sure where I got the idea it was a Mk 2, but it is probably attributable to being early in the morning, not enough coffeee and being in a hurry to get to work.

IP is less critical on the Mk 20 as it essentially stable regardless of tank pressure and will function as well at 120 psi as at 145 psi. SP specs call for the IP to be set within this range so your reg could be operating anywhere within the range and still be within spec.

I know for a fact that a the Mk 20 will work fine with a long hose as I use Mk 20's and have used both 6 ft and 7 ft hoses on my Mk 20's and have never had any problem.
My best guess is that there is still possibly some odd type of sympathetic resonance occurring between the first stage piston and the second stage

A piston vibrating in a Mk 20 (or similar balanced piston reg) is almost always due to inadequate lubrication of the HP O-ring and if I had it on the bench that is the first thing I would check.

I would also check the IP and if posssible add a shim under the mainspring to increase the IP slightly. In some cases the shim also seems to have a dampening effect on any resonance. Either way changing something in the system is normally enough to eliminate any sypmatheic resonance that is occurring as it changes the frequency of one of the offending parts so that the parts no longer resonate with each other.

But to be thorough, I would also check the second stage for problems. Excessive slack in the lever can cause a flutter effect in the second stage. The G500 is single adjustment balanced poppet design, so the lever height is primarily controlled by the orfice adjustment and its effect on how far inward the poppet is pushed. Spring pressure in the second stage is also adjusted via the adjustment knob but this has no significant effect on the lever height. It is possible that if the second stage were improperly adjusted with the orifice to far inward creating excessive slack in the lever that a fluttering of the poppet could occur. This is a long shot though as I would expect that this would result in a flutter regardless of hose lenght used.

In short it is a systemic problem and it is pretty hard to diagnose or fix without checking everything in the system. In most cases, second stage problems originate in the first stage, so you want to double check and adjust everything there before proceeding to the second stage.

 

[DS tank wipe]

Get an Apeks solve all your problems

 

[DA Aquamaster]

Get an Apeks solve all your problems

Well...that would solve the immediate problem, but long term you would still have the problem of owning and having to use an Apeks, and compared to a nicely tuned Mk 25 G500, an Apeks breathes like a rock. IMHO of course.

 

[trevinkorea]

Thank you very much DA Aquamaster.

I'll print your post and go back to the SP tech and see if we can get this resolved.
(provided of course that he can get over his ignorance when it comes to anything different.)

You are truely a wealth of knowledge.

Trevor