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

[rsingler]

I have a handful of seats for mine and will continue to use them until I don't have any more.

Scubapro still sells MK15 seats as of the 2020 price list. VDH has a few NOS as well. Let me know if you want me to order you some.

 

[axxel57]

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?

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.

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.

Rob, actually I don't believe that the cone seat really plays an important role in the stability of the 1st stage air output.
I'm very with Halo's arguments and think that the reason for the more stable air output of the MK10 is really the lightness and the guiding of the piston in the MK10 body as promoted by SP in their catalog.
They didn't mention the new cone seat in their adds, so I guess, as far as I know SP promotion for their products, that they didn't know how to use it for their advertisements......
As I mentioned in the other post, I think that the absolute air output was later their main concern, so with the new pistons in the MK20/25 they delivered enough air at full tank, so that they did not have to worry about the output at near empty tank.
I couldn't say how much a MK25 is flowing at 500psi, but if it can flow 9600l/m at full tank, who cares if the 'old' configuration is only flowing 6600l/m, if it would be for example like that?
Under these conditions air output stability is of nobody's concern anymore.
And I'm sure that Halo is right pointing out that the precision of production has probably quite a lot improved and with the composite piston is also weight no issue anymore.....

 

[Kupu]

 

[Golan68]

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.

Angelo,
I saw that you "played" with retainer hole of the mk5 when you tried to put the new style din conversion [putting a shim with a round hole]. didn't it make a noticeable difference on the behavior of the regulator ?
As Rob said , indeed intriguing question, and as far as I can see, their are several factors that make the huge difference, but mostly the "way" the high pressure from the tank meets the seat. That said, the proportion between the part of the HP air seeing [or meeting] the piston and the part that "sees" the seat. With the edition of the concave seat and probably the angle of the entrance to the piston bore. So probably the round edge piston was not just to save the seat, the smoothest the way the air will enter the bore the better flow.
One can't ignore the fact the mk10 with smaller piston/bore gives more air [I didn't know that and was very surprised]. Also, the fact that the valve of the tank becomes a limiting factor makes me think that it's better to have small bore if you want to "play" with the numbers , or simply have more stable ip all the way.
One thing I must say, from user observation, there is a difference between piston and diaphragm , last time I dived I compared my Pilot on Mk14 [6500 lpm] vs the mk25... difference is defiantly noticeable. Now that you told me that Mk5 is half of mk14 and mk10 is equal, I realized I must compare those too.

 

[MR12111]

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.

Hello Looks like you've worked on a Lot of Scubapro stuff .. i was a tech in the 80's in a Scubapro Shop here in Florida ..did a LOT of mk5's and some mk10's along with everything else in the day ....
Hope you can help me .. I feel sorta stupid ......After being burnt out with "the industry" ..Boat Capt/Instructor......15 years later ... I now think maybe I'll try some recreational diving ...
So trying to get a reg together to use ..My old Sherwood 3100 is shot and their's no Parts ..So I'm thinking of using this mk20 I have .. 1 shop I divemastered in got me to buy it thinking it would look good in front of their customers ... I didn't really like it ..Neither the D400 or the 250 second stage compared to the MR12 I had been using for decades ..maybe it's just what I'm used to ..
sorry this is so long ..The Question .. mk20 is different in several ways than mk5 or 10 ..... I am having trouble getting the piston in due to the 2 "wiper" seals ..I can get 1 in and the oring the 2nd one just want's to extrude from the piston whenever I try to get it in ..Cannot find any info on this ... Is it just me ?? Thank You for any Help You san Give ..Don J .

 

[lexvil]

Hello Looks like you've worked on a Lot of Scubapro stuff .. i was a tech in the 80's in a Scubapro Shop here in Florida ..did a LOT of mk5's and some mk10's along with everything else in the day ....
Hope you can help me .. I feel sorta stupid ......After being burnt out with "the industry" ..Boat Capt/Instructor......15 years later ... I now think maybe I'll try some recreational diving ...
So trying to get a reg together to use ..My old Sherwood 3100 is shot and their's no Parts ..So I'm thinking of using this mk20 I have .. 1 shop I divemastered in got me to buy it thinking it would look good in front of their customers ... I didn't really like it ..Neither the D400 or the 250 second stage compared to the MR12 I had been using for decades ..maybe it's just what I'm used to ..
sorry this is so long ..The Question .. mk20 is different in several ways than mk5 or 10 ..... I am having trouble getting the piston in due to the 2 "wiper" seals ..I can get 1 in and the oring the 2nd one just want's to extrude from the piston whenever I try to get it in ..Cannot find any info on this ... Is it just me ?? Thank You for any Help You san Give ..Don J .

Lots of grease, do you have a “bullet” to guide the piston end past the HP seals? I assume you do and while you can get y without it on the 20 it will help guide everything as you push the piston in. The 20 can be upgraded to a 25 easily.

 

[halocline]

.The Question .. mk20 is different in several ways than mk5 or 10 ..... I am having trouble getting the piston in due to the 2 "wiper" seals ..I can get 1 in and the oring the 2nd one just want's to extrude from the piston whenever I try to get it in ..Cannot find any info on this ... Is it just me ?? Thank You for any Help You san Give ..Don J .

Usually the issue getting the piston in is at the shaft end. Despite what some of the bulletins say, I always use a bullet. I also use the peterbuilt bushing tool; it installs the bushings perfectly and the other end holds them in place while you install the piston.

Then, you screw the ambient chamber/turret assembly onto the main body. If this is where you are having trouble, the first issue might be that you have a piston that does not use 2 o-rings on the piston head. the earlier MK20 pistons, both all-steel and the brass tipped steel, use one o-ring and a plastic split ring washer. I'll try to attach a photo.

If you have either the 1st or 2nd piston from the left, you don't use 2 o-rings, you use the plastic split ring to hold a single o-ring in place.

 

[MR12111]

Usually the issue getting the piston in is at the shaft end. Despite what some of the bulletins say, I always use a bullet. I also use the peterbuilt bushing tool; it installs the bushings perfectly and the other end holds them in place while you install the piston.

Then, you screw the ambient chamber/turret assembly onto the main body. If this is where you are having trouble, the first issue might be that you have a piston that does not use 2 o-rings on the piston head. the earlier MK20 pistons, both all-steel and the brass tipped steel, use one o-ring and a plastic split ring washer. I'll try to attach a photo.
View attachment 758841
If you have either the 1st or 2nd piston from the left, you don't use 2 o-rings, you use the plastic split ring to hold a single o-ring in place.

Thanks for the reply ..Yup .I have a piston "bullet" ...thing is when you go to use it the 3 piece bushing/o-ring deal pushes out the top of the reg .. I read about a trick putting the spring and seat in to hold the bushing/o-ring assy while you put the piston in ..I did that ..had it installed ..These "newer" pistons seem less sharp than the old mk5 & 10 .. anyhow I got that together but couldnt get the cap on ..It went past the first wiper ring and the o-ring but I think the o-ring caused the second wiper to extrude rather than allow the piston to go in ..Looks like the mk25 uses a different Piston without the wiper rings ....This thing reminds me of an old Dacor reg ..600 or 900 model # I think ...Had 65 Parts ..Pain in the Butt .. Thanks Again for and advice you can give me ..thinking of looking into an old mk10 ..

 

[MR12111]

Lots of grease, do you have a “bullet” to guide the piston end past the HP seals? I assume you do and while you can get y without it on the 20 it will help guide everything as you push the piston in. The 20 can be upgraded to a 25 easily.

Thank You for the reply ..Please see the description of the problem I'm having below in the post I answered ... Thanks Again Don ..

 

[MR12111]

Usually the issue getting the piston in is at the shaft end. Despite what some of the bulletins say, I always use a bullet. I also use the peterbuilt bushing tool; it installs the bushings perfectly and the other end holds them in place while you install the piston.

Then, you screw the ambient chamber/turret assembly onto the main body. If this is where you are having trouble, the first issue might be that you have a piston that does not use 2 o-rings on the piston head. the earlier MK20 pistons, both all-steel and the brass tipped steel, use one o-ring and a plastic split ring washer. I'll try to attach a photo.
View attachment 758841
If you have either the 1st or 2nd piston from the left, you don't use 2 o-rings, you use the plastic split ring to hold a single o-ring in place.

Mine looks most like the Black one ... but the 2 split rings are the same thickness ..I am the first to take this apart ..Imagine my surprise when I took the top cap off to inspect and maybe "flip" the H.P. seat ..It's not in the cap any longer ...weird