What’s the difference between a MK5 and a MK10?

[Eric Sedletzky]

Just as the title says, what’s the difference?
I have a 5 and a 20 but not a 10.
How is the 10 better than the 5, or is it?
Is a 5 and/or 10 better than a 20/25?
Or, is all this a matter of subjective emotional attachment and not based on anything practical or mechanical superiority?
Am I missing out?

 

[axxel57]

Technically there is quite some difference between the MK5 and the MK10 or MK20/25.

The biggest 'problem' with the MK5 was the uneven air output over the course of a dive.

While delivering at full tank 2464 liters a minute, that was reduced to 1359 liters per minute at 50 bars.

In the new MK9/10 design the piston gland was now running in the MK10 body and not in the cap and the piston diameter was reduced. That lead to a more precise and faster reaction and produced an almost even air output of the 1st stage( 2265 liter/min at full tank, 2067 l/m at 50 bars).

As one can see, the air output of the MK10 is a little less than the one of the MK5, so it was clear that the next main design should deliver clearly more l/m.

The MK20 with the same basic design had now again a bigger piston which lead to a theoretical air output of 8500l/m and the MK25 even 9600l/m and to a problem to most of the tank valves on the market which were not able to flow that amount of air per minute..........

 

[Angelo Farina]

The MK10 was the best ever: simple, reliable, repair kits yet available, constant performances (good enough for any real case, the extra air flow of MK20-25 is useless), easy to service.
I have 5 MK5 and one MK10, and the last is, of course, the better. However MK5 are good enough for normal rec diving, particularly if matched with a balanced second stage (109 modified or 156), or, for top notch performances, a G250.

 

[lexvil]

The difference is 5

 

[thbcthomas]

The difference is 5

This is what I love about scubaboard, the deep technical info that you can't get anywhere else. If you were to ask your lds technician what is the difference, he probably would have no idea. The people at Starbucks are looking at me like I am crazy as I spit out my coffee reading @lexvil answer.

 

[lexvil]

Ok, now a little more serious answer.
So long as you can get seats and your piston is good and you upgrade the swivel retainer there is no reason to stop using a MK5, the MK 10 makes converting to DIN easier the only negative to the 10 is it can give a bit of erratic IP if the HP o ring isn’t lubed really well. The MK 15 is, for me anyway, a good source of port plugs. The MK 20 is pretty much the pinnacle of piston regulator design best represented in the Atomic first stages, MK 25 adds a nice but unnecessary fine tuning of the IP.

I’m now completely locked in on the MK 17 because I’ve seen a lot of sealing surface wear on unsealed pistons due to my gritty shore diving, the 17 makes first stage clean up a snap.

 

[rsingler]

In the new MK9/10 design the piston gland was now running in the MK10 body and not in the cap and the piston diameter was reduced. That lead to a more precise and faster reaction and produced an almost even air output of the 1st stage( 2265 liter/min at full tank, 2067 l/m at 50 bars).

This is an intriguing comment. Why should it matter where the piston head land sits? Why did placing the piston head inside the body instead of inside the cap make piston action more precise? I can see how it might have helped alignment during piston travel. But decreasing the piston head diameter made Mk10 lockup less crisp, IMO.
Help me understand the physics of how the design preserved airflow as tank pressure decreased...

Let's look at these two cross sections. Ignore that the Mk10 is of the Mk10Plus. That's the only cross section I have, but the only difference is the piston end and seat. The rest is the same as the old Mk10.

What is it in these two diagrams, other than piston head diameter and piston bore diameter that is different? What preserves flow on the Mk10?

Here's a 15 year old thread with a post from one of our other Scubapro experts, @DA Aquamaster.
Scubapro Regs... What's the difference? Which one to get?
He points to concave seat design as a major factor in improving flow. But you can now use those seats in the Mk5 as well. What do you think, @axxel57? Do you think a Mk5 with a cone seat would have better preserved flow at low tank pressures?
BTW, thank you @axxel57 for this tremendous historical knowledge! And @DA Aquamaster, I know you're still lurking out there, lol! Any chance you could weigh in?

The MK 20 is pretty much the pinnacle of piston regulator design best represented in the Atomic first stages, MK 25 adds a nice but unnecessary fine tuning of the IP.

Buuut...

I’m now completely locked in on the MK 17 because I’ve seen a lot of sealing surface wear on unsealed pistons due to my gritty shore diving, the 17 makes first stage clean up a snap.

Ah, another fanboy for sealed regs!
Atomic Z3, anyone? No? Don't like sticking all that gunk in there?
Scubapro Mk19, perhaps?
And then there's the Sherwood SR series. Piston. Dry sealed. Huge flow. But never gets any love.
Turret. Environmentally sealed. High flow. Stable IP.
Ladies and gentlemen, we have reached Fukuyama's "The End of History."
That is all.

 

[rhwestfall]

Sealed diaphragm for me. SP Mk-17, HOG, Deep6

Then there is my double hose regs....

My piston firsts see little water anymore (mk-2 excluded).

 

[Couv]

This is an intriguing comment. Why should it matter where the piston head land sits? Why did placing the piston head inside the body instead of inside the cap make piston action more precise? I can see how it might have helped alignment during piston travel. But decreasing the piston head diameter made Mk10 lockup less crisp, IMO.
Help me understand the physics of how the design preserved airflow as tank pressure decreased...

Let's look at these two cross sections. Ignore that the Mk10 is of the Mk10Plus. That's the only cross section I have, but the only difference is the piston end and seat. The rest is the same as the old Mk10.

What is it in these two diagrams, other than piston head diameter and piston bore diameter that is different? What preserves flow on the Mk10?
View attachment 606673
Here's a 15 year old thread with a post from one of our other Scubapro experts, @DA Aquamaster.
Scubapro Regs... What's the difference? Which one to get?
He points to concave seat design as a major factor in improving flow. But you can now use those seats in the Mk5 as well. What do you think, @axxel57? Do you think a Mk5 with a cone seat would have better preserved flow at low tank pressures?
BTW, thank you @axxel57 for this tremendous historical knowledge! And @DA Aquamaster, I know you're still lurking out there, lol! Any chance you could weigh in?



Buuut...



Ah, another fanboy for sealed regs!
Atomic Z3, anyone? No? Don't like sticking all that gunk in there?
Scubapro Mk19, perhaps?
And then there's the Sherwood SR series. Piston. Dry sealed. Huge flow. But never gets any love.
Turret. Environmentally sealed. High flow. Stable IP.
Ladies and gentlemen, we have reached Fukuyama's "The End of History."
That is all.

The turret retainer hole size in a MK10 is just over 5.5mm compared to the MK5's turret retainer hole size of just over 4mm (some MK5s retainer holes are even smaller.) I'll leave the π r2 to you, but the difference is substantial.

 

[uncfnp]

Isn’t the design of the newer versions also suppose to handle the higher tank pressures of the HP tanks?