Scubapro Mk25/S600 Performance Questions

[Manuel Sam]

For those of you who are familiar or routinely service the Scubapro Mk25/S600 reg, I thank you in advance for your help and insights.

I bought the above reg thru the DAN auction some 7-8 years ago - it is not a grey market reg.

I have religiously brought it in for service to a Scubapro authorized service dealer on an annual basis - for the past 4-5 years with the current LDS I have been using.

It is my habit to hook up the reg to a tank when I go pick it up after annual service to make sure it works OK. This is the first time I've encountered this issue.

When it was handed to me, the inhalation resistance adjustment knob was already opened about halfway counterclockwise (CCW). I turned the Predive/Dive lever to Dive, took a few puffs and encountered some resistance and hesitation.

I then cranked it further CCW until just a hair short of fully open. At this setting, the inhalation effort was close to what I am normally used to - smooth and continuous.

At the other end of the spectrum, with the inhalation resistance adjustment knob basically closed (fully clockwise), getting air out of the reg took a lot of effort. You would not want to dive with it in that state.

In my experience with this reg, I have never had to go beyond cracking it open to get it to breathe like a well-conditioned Ferrari. In my view, I can't imagine that manufacturer intent was for the user to adjust the knob to make the reg even breathable - until today, it has always been breathable even with the knob closed. In fact, the reg has always been breathable and divable regardless of knob position: it certainly was when I first took it out of the box 7-8 years ago.....until today. To me, the knob is there only to finetune the flow to one's liking.

Bottom line is that my reg went from performing like a Ferrari to performing like a Hyundai (no offense intended).

I welcome your comments on what your experience has been and whether you think the reg was serviced and tested correctly.

Thanks.

 

[BoltSnap]

Did you discuss the issue with your LDS technician? I normally adjust my regulator all the way open for the easiest breathing when I am using it U/W and all the way in when I have to take the second stage out of my mouth as when doing a surface swim or getting in or out of the water. The SS shouldn't be too easy to breath and consequently higher chance of free flow when the adjustment knob is in the all-the way-in position.

 

[Manuel Sam]

Thank you BurhanMuntasser. My visit to the LDS yesterday to the LDS was my second one to go pick up the reg. On the first one, you could not get any air out of the reg when the knob was all the way in.

I respect fully what you are saying, and that would seem to substantiate what the LDS is claiming. However,

1. That would imply that all prior years of service on this reg were done incorrectly, and
2. If I have to crank up the knob all the way in order to make it easy breathing, I have no further adjustment should there be a future situation when I really need a bit more flow - whatever the reason may be.

I would further comment that the procedure that you just described of having to constantly open it and close it with every dive start and end of dive is a royal pain. Again, in my humble opinion, the reg should allow you to dive comfortably no matter what the setting of the knob is. You should be able to set it once and forget it.

If you are doing what you just described for every dive - and honestly, I have never had to do that and have never had problems with freeflow - then my thoughts are that turning the lever from Dive to Pre-dive ought to accomplish what you are now doing by adjusting the knob in and out all with every dive.

 

[diverdoug1]

My MK25 and S600 still breath fairly easily when "cranked down" all the way, and are close to free flow when open all the way.

 

[Jim Lapenta]

I would suggest you get a copy of scubatools reg savvy or airspeed press's regulator repair and maintenance. Either will help you get a better understanding of how a reg is supposed to work. It sounds like your reg is tuned the way it should be. The dive pre dive lever is to help prevent free flows on the surface by directing some of the flow towards the diaphragm in the event you drop it in the water or hit the purge button by accident. In the pre dive position it will make the reg somewhat stiffer.
The inhalation effort knob is supposed to do exactly what my friend Burhann said. With it all the way open the effort is easiest and turned back it should be somewhat stiff. How it behaves for you and where you want it set is something you should determine and then tell your tech to adjust the cracking pressure to your satisfaction. If you don't know how to tell him to do this or what you want the reg set at, it's time to get either of those books and find out.
If a reg is properly tuned and working as it should there will be a very noticeable difference in breathing effort between settings. If there is not the reg was likely not done correctly.
In addition unless the reg is seeing several hundred dives a year there is no need to have it done every year. Many regs can go two or three years between service. I would hazard a guess that a few of those times you took it in to be serviced what they did was inspect it and little more. Did you get the used parts back every time?
Another thing to consider is that over time a new seat will begin to get broken in and the effort throughout the range will get easier. I'm guessing they finally put a new seat in and could have spent a litte more time breaking it in. What is the current Intermediate Pressure at the first stage? This can have an effect as well on breathing effort and is something an experienced diver should know how to check. The gauge to do it can be had for as little as ten - fifteen bucks. Just plugs into your lP inflator hose.

 

[zf2nt]

You should normally dive with the knob fully open. The reg should NOT leak air in this position, and it should not even be close to free-flowing. Your LDS tech should have a magnehelic gauge and be willing to show you that the reg is properly tuned with 1.1 to 1.3 inches of water cracking pressure when the knob is fully opened. (Any properly trained tech will know what this means and should be willing to demonstrate it to you. It only takes a few seconds.) The "Dive/Pre-Dive" lever will have no bearing on this. It is there so that in the Pre-Dive position the airflow inside the second stage is shunted to NOT create a venturi effect on the diaphragm and so sustain a free-flow. If you put it in "dive" mode and hit the purge button, the reg should then free-flow by itself; in "pre-dive" mode, it will not.

The only reason you would have the knob in anything other than the fully-open position is if it has been a while since the reg was serviced so that, as Jim mentioned above, the LP seat has taken a set to the orifice knife-edge and so has a groove worn into it. If the reg leaks a slight bit of air, then turn the knob just enough to stop this leak and that counters the wear on the surface of the seat.

The only reg I have ever seen that I like better than the MK25/S600 is the MK25/G250V I'm using now. Properly tuned, that is a fantastic piece of dive equipment.

 

[Manuel Sam]

Hi Diverdoug1,

Thanks for your input and help. Yours is the third feedback that I've gotten (both within and outside of the Forum) that has the knob cranked down to almost closed. This just lends itself to more confusion. I hope that the folks from Scubapro will eventually weigh in with an "official" opinion.

Hi Jim,

Thanks as well for your input and help. Even tho we don't see eye to eye on the subject of where the inhalation effort knob ought to be set at, you obviously know your stuff and I appreciate your sharing your knowledge.

I wasn't aware until yesterday when I started searching in Scubapro's website that the "annual" service to maintain their Parts Life Guarantee is now two years or 100 dives. Indeed, just as you said, I've never deemed it necessity - just a requirement like paying taxes (or else) - to have it serviced annually, given that I am a wimpy warm-water diver who does a mere 50-80 dives a year when I go on trips to the tropics. Diving in New England or in quarries is not my cup of tea- for one thing, because the water is cold, there's the "shrinkage" factor, which is really bad for the male ego. But I digress.

I did get parts back most of those times.

While not totally disagreeing with you, I still find it very odd that this is the first time in 7-8 annual services that, with the knob set at closed or almost closed, which is where I have always had it, I can hardly get any air out of the reg. This is, of course, a somewhat subjective thing, but I wouldn't even call the present state of that reg (with the inhalation effort knob cranked down to closed) as somewhat "stiff". "Somewhat stiff" is going against a half-knot current.......this is a 5-knot current. I'd have to be Hoover vac to get enough air out of the thing. Might be fine for a freediver, but not for scuba divers, I don't think.

And I reassert that all these checks were done with the Dive/Pre-dive lever set on Dive, altho to tell you the truth, I have never noticed much difference in inhalation effort either way. This is based on countless times that I left it in Pre-dive and jumped in. Like I said, when the reg works like what I am used to, it works like a well-tuned Ferrari.

I think that if I tell the LDS technician to adjust the cracking pressure down below what is considered normal, he ought to be able to do it. But that just begs the question as to why I've never had to ask for such a deviation before, and still got a reg back that worked to my liking. I'll keep you posted on this.

As for the thought that a new seat was put in, I'll have to ask the LDS. But still, when new, presumably the reg had a new seat too, and it was never like this.

The beauty of this reg is that, for the most part, it has worked almost like I didn't have a reg in my mouth, with only minor adjustments made to the inhalation effort knob after each time it was serviced. I've never ever had to crank it up to the fullest like I am having to do now in order to get a comfortable breath out of it. It's always been at most a 1/4 to 1/2 turn CCW from closed.

Thanks again.

Hi z2fnt,

Thanks for your input and help.

Ok, so now I have three people saying fully open and three almost closed. Hopefully someone from Scubapro will chime in.

Regardless, I think that the ultimate answer is still, as Jim suggeested, to tell the technician at the LDS to adjust it to what I am most used to.

I recall using a G250 in the mid-90's(?). It was a rental so I don't know what first stage it was hooked up to - not sure if the same as the G250V that you mentioned, but at that time, it was, to me, regulator heaven. I'd be hard-pressed to say which one I like better - G250 or S600 - because I don't have the two here side-by-side to make the comparison, but it was the first time I ever felt that I was breathing u/w with no reg in my mouth.

Thanks.

 

[Pavao]

This is a very simple thing, so, I will not give you an overly complicated answer.

I will assume it is fine tuned properly...

Knob all the way open = Best performance (Ferrari), that's where "you" want it always.
Knob all the way closed = Worst performance (Hyundai), I would need a very good reason to have it that way, even when scootering it is not near closed.

I own 7 MK25/S600's

 

[Jim Lapenta]

My adjustable seconds are all set so that there is a very slight free flow with the knob all the way open. Specs may say 1 or 1.1 for new reg but when you get some experience those numbers are more like guidelines. I actually prefer a cracking pressure of around .8 to 1.9 or whatever it ends up being. But I do not set new regs like that. Those are my own preferences. And that is what they usually end up at after a few dives and the seat settles in. I never dive with the knob fully open. It is usually a 1/4 turn back or so.

 

[mike_bayer]

This is exactly how I like my G250 setup but I can't seem to find a LDS to do it. They all set them very conservatively nowhere close to free flowing dialed all the way out.

The difference is tremendous when set properly.

My adjustable seconds are all set so that there is a very slight free flow with the knob all the way open. Specs may say 1 or 1.1 for new reg but when you get some experience those numbers are more like guidelines. I actually prefer a cracking pressure of around .8 to 1.9 or whatever it ends up being. But I do not set new regs like that. Those are my own preferences. And that is what they usually end up at after a few dives and the seat settles in. I never dive with the knob fully open. It is usually a 1/4 turn back or so.