MK17 / G250V free flow

[pheel]

Hello everyone,

1 year ago when I had to choose for a reg I was looking mainly for something that could handle cold water. There is a SP dealer and also a Apeks/AL dealer near where I live. Both have good reputation. After some research I finally chose the SP MK17/G250V instead of the Apeks XTX50. The SP was a little cheaper and I really like that SP shop.

This winter I took the ice diving class and got a free flow en less than 10 feet of water (33-34 F). I realised that I forgot to adjust the knob of the second stage for minimal air flow. The second dive went well (with the knob set to minimal air flow).

Few days after I went to the shop for reg check out. I told the owner it was a deception for me to get a free flow in such shallow water with a reg supposed to withstand such cold water. To my surprise, he got irritated, told me that he sells those reg to most of his customer for icediving, never saw any freeflow. He then told me that it may have been caused by that fact I went diving in the caribbean the week before. I did also few pool dive and apparently that is not good for free flow. Those reasons seem BS, the typical customer service that claim it is always the customer fault, not the product.

I wasn't that upset with that and put the blame on the adjustment knob. However, I talked to my buddy today (he has the same MK17 / G250V bought at the same time) and yesterday he went diving with other fellow divers. Guess what, he got a free flow in a quarry at 110' 42F. He had to use the octopus of another diver. The freeflow stopped when they finally reached 15'. Apparently it wasn't very funny. In his case, the adjustment knob was fully open (max flow).

Well, now I'm thinking that maybe I should have bought the XTX50...

Any comments or bad experience with SP ?

thanks

 

[Hank658]

pheel, a couple of questions regarding your gear:
you mention that you have had the reg about a year. Have you had it serviced recently? Are you diligent about cleaning your regs after all of your dives, whether fresh, pool or salt water?
The reasons for a freeflow that you mention hearing don't hold much water with me (pardon the pun). A Mk17/250V should perform exceptionally well in the conditions that you describe. If your shop is a SP dealer they should also be able to service and adjust your reg. The second stage might be set to too light an inhalation effort. The first stage might need an IP adjustment. With the right tech and the proper tools these are fairly straightforward. Of course, without seeing your reg these are only guesses on my part, but from my experience a Mk17/250V combo should cause you no regret for your kind of diving.
If your shop cannot service your reg then that's a whole other story.

Hope this helps a bit...

 

[SangP]

If you've recently serviced the reg it may be it's tuned on the high side. I've experienced free flows a lot of times n it's just a matter of detuning it which is easily done.

SangP

 

[pheel]

thanks for the answers

Yes, I'm pretty careful with my gear as far as cleaning goes. Same thing for my buddy.

We both had our reg serviced right after our first free flow under ice. The tech who did it is the same who told us about the pool and caribbean thing...When I took back my reg he told me he couldn't find anything that may have caused the freeflow.

What do you thing of the adjustement knob? Should it be set to minimal air flow when diving in those kind of condition?

 

[tfsails]

The adjustment knob does not regulate air flow; rather, it regulates the effort required to actuate the demand lever and deliver air. This is known as "cracking pressure". Most second stages have their cracking pressures set to between .8 and 1.4 inches of water.

Neither the Caribbean nor the swimming pool should have any effect on this problem one way or another. Your tech is blowing smoke up your ass on that one.

If you're breathing rapidly in very cold water the temperature drop caused by the rapid flow of once-pressurized air from the tank can cause the water in the pressure port(s) of the first stage to freeze which will impair the operation of the first stage. This usually results in a free-flow in the second stage. Breathing slowly and deeply should alleviate this condition. No way around this one--it's one of the laws of physics. It's the opposite of what makes a tank get warm when you're filling it.

Is this Mk-17 environmentally sealed? If not, can the dealer install a sealing system on it? Sealed first stages rarely freeze up because water cannot get inside them, hence no ice.

 

[halocline]

If you're breathing rapidly in very cold water the temperature drop caused by the rapid flow of once-pressurized air from the tank can cause the water in the pressure port(s) of the first stage to freeze which will impair the operation of the first stage.

The MK 17 is sealed, so there's no water in the ambient chamber. I suspect this freeflow was in the 2nd stage. I would make sure there's no hose protector against the 2nd stage, turn the venturi assist all the way off, maybe turn the cracking pressure knob in a little, and follow tfsails advice about breathing slowly. They say not to breathe on the surface if the air temp is also really cold.

When a 2nd stage is set to a really low cracking pressure, and has some venturi assist, in normal swimming position the diaphragm is about an inch deeper than the exhaust valve, which means the reg is more likely to flow a little between breaths. That's due to case fault geometry. A slight flow will really cool down the 2nd stage, which I guess could freeze it up.

There's a tradition of lowering the IP for really cold water use, I suppose in an attempt to slow the potential flow to the 2nd stage. I'm not sure how effective it is; you still have a very high flow 1st stage, and a balanced 2nd which essentially negates the varying IP.

Who knows what the dive shop owner/salesman/"tech" was talking about. They have been known to, ummm, postulate some interesting ideas about regulators.

 

[pheel]

Is this craking pressure adjustment cause freeflow then ? If effort in minimal we may then inhale more air in less time causing the flow to be higher at some point ?

Yes, of what I know, MK17 is environmentally sealed.

 

[pheel]

Thanks Matt,

Yes when ice diving we take the first breath under water, we were told to do so.

What setup do you guys have ?

p

 

[elan]

Any reg can free flow, you really need to use proper protocols of regulator handling when ICE diving. You regulators have to be dry inside out and stay dry all the way till you get below the surface. You get single drop of water water on your tank valve or you get moisture in the reg when you are on the surface and you are screwed. It is very good idea to dry your gear out (make sure you take the first stage cup off) including the tank valve inside a warm place, say at home, then rig your gear up and breath for some time from it, then load the gear into the truck and go diving. Make sure the second stage does not get wet. Before going underwater, Put the cranking to the lowest setting and turn off the venture. When I was following those procedures I was diving 36F water with 10F on the surface and I got no single free flow. Once I did not really followed that and just put the regs which were wet from the dive a day before and I got 2 regs out of 3 flowing in 37F water.

When it comes to ice diving you need to make sue the gear is dry until submerged. Do not breath your regs on the surface.

 

[DA Aquamaster]

42 is not all that cold in terms of what a Mk 17 G250V can handle. I routinely have mine in water as cold or colder than that at depths well below 60 ft. I have had the Mk 17 G250 in water 35 degrees at 150 ft and not had any issues with no special care taken to prevent a freeflow. In 25 years of cold water diving, the Mk 17 is hands down the most bullet proof cold water first stage I have ever seen.

I tune my MK 17's for an IP of 145 (the upper end of the scale) and tune the second stage for minimum inhalation effort and dive with the knob adjusted for minimum effort and again I have never had a freeze flow with it, even at depths to 150' in 33-35 degre water.

No offense intended, but if there was not an issue with a defective seal, I suspect technique is an issue. As noted above, you want to avoid supercolling the reg below freezing and pre-breathing out of the water can do that. On the sealed Mk 17, that won't really matter but it could be an issue on the second stage. There is also a need for common sense. If the air temps are well below freezing and you get in, the rg is already colled well below freezing even if you have not been breathing it. in that case, either take a great deal of care to prevent any water from getting inside the second stage, or let it soak long enough to warm to the water temp before breathing off it (not always possible without risking a free flow).

As mattboy indicates, heat transfer is important and pulling back any hose covers to expose the metal fittings will help. On the G250V the large splined adjustment knob and the splined knob on the inlet fitting improve heat transfer.