Why was the piston reg invented?

[Eric Sedletzky]

I'm not sure WHEN it was invented but am pretty sure it was long before Cousteau. Unbalanced and balanced flow-through pistons have been preferred for industrial regulators that require high flow rates for long time.

I routinely get O2 cylinders exchanged at the welding supply that have a first hydro stamp date in the teens and twenties.
The pressure of that gas had to be brought down somehow.

---------- Post added February 15th, 2015 at 12:52 PM ----------

There are two basic types of piston design, and they differ quite a bit. The flow-by piston, like the MK2, has the distinction of no dynamic o-rings being subjected to supply pressure, an extremely low parts count, and the resulting stellar record of handling abuse for years without maintenance.

The flow through design (MK5 et al) is also extremely simple and allows for balancing (well, almost balanced) without the complexity of a balance chamber, and flows a lot of air, with very stable IP and very quick recovery. When the MK5 came out, it's performance was outstanding and rebuilds were a breeze. Piston regs weren't always like the MK25 and atomic.

I have a MK5 and from everything I've seen it's about as good as SP ever got.
I scratch my head as to why they felt they needed to continue trying to improve on something that seemed like it had been perfected.
A comparison would be Aqualung with the inerds of the Conshelfs, that style is about as good as it gets, but the difference is they knew when to stop and keep a good thing.

 

[Akimbo]

I routinely get O2 cylinders exchanged at the welding supply that have a first hydro stamp date in the teens and twenties.
The pressure of that gas had to be brought down somehow...

Welding and burning is a pretty low flow demand. The BIG regulators were used for steam and compressed air.

…I have a MK5 and from everything I've seen it's about as good as SP ever got.
I scratch my head as to why they felt they needed to continue trying to improve on something that seemed like it had been perfected.
A comparison would be Aqualung with the inerds of the Conshelfs, that style is about as good as it gets, but the difference is they knew when to stop and keep a good thing.

It’s probably more complex than that. Before breathing machines that actually measured performance in real-time at depth it was pretty hard to know exactly where the restrictions were. There was a lot of finger-pointing at the first stage and hoses in the late 1960s.

Also, anti-freeze characteristics weren’t such a big deal then since so little was being done in wetsuits. There have been a lot of refinements to diaphragm regulators over the years. Minute changes in angles and finish can have huge impacts on turbulent flow. Good piston regulators still have higher flow rates than diaphragms, just look at the flow path and orifice sizes. The big difference is we now know what is “good enough”.

 

[scubafanatic]

Higher potential performance (flow rate), rotating turrets for optimal hose routing and up or down mounting, failsafe unlike diaphragm, simple and stable. A classic regulator battle would be the USD/AL Conshelf XIV diaphragm vs. the SP R109/MkV piston. N

Interestingly enough, I've got a pair of SP MK 18's, which offer BOTH diaphragm 1st-stages AND rotating turrets for optimal hose routing.

---------- Post added February 15th, 2015 at 02:56 PM ----------

Higher potential performance (flow rate), rotating turrets for optimal hose routing and up or down mounting, failsafe unlike diaphragm, simple and stable. A classic regulator battle would be the USD/AL Conshelf XIV diaphragm vs. the SP R109/MkV piston. N

I like the classic 'look' and simplicity of the SP MK 5/109's as well !

 

[Eric Sedletzky]

It’s probably more complex than that. Before breathing machines that actually measured performance in real-time at depth it was pretty hard to know exactly where the restrictions were. There was a lot of finger-pointing at the first stage and hoses in the late 1960s.

Also, anti-freeze characteristics weren’t such a big deal then since so little was being done in wetsuits. There have been a lot of refinements to diaphragm regulators over the years. Minute changes in angles and finish can have huge impacts on turbulent flow. Good piston regulators still have higher flow rates than diaphragms, just look at the flow path and orifice sizes. The big difference is we now know what is “good enough”.

I don't see the benefits of super high flow rates of a piston if the flow rate of a diaphragm is still 5 times better than it needs to be in any practical diving application.
I don't know if a need will ever arise when 30 divers will need to suck off the same reg at 300 feet.
One benefit I know about pistons is they run air tools better topside, but what about a freeflowing reg?
Has anybody thought about super flow rates emptying a tank in nothing flat?

 

[halocline]

I have a MK5 and from everything I've seen it's about as good as SP ever got.
I scratch my head as to why they felt they needed to continue trying to improve on something that seemed like it had been perfected.

There are two sides to it, I suppose. One is that most gear companies will constantly come out with new 'improved' models to sell to existing owners. The other is that the later BP firsts did have actual performance improvements; the bushing system on the hp o-ring does really help with tolerances around the piston shaft, and consequently better HP cylinder performance, and it 'fixed' the problem of badly trained and/or careless techs ruing MK5/10 bodies by digging out the o-ring with an ice pick. And the rounded piston edge on the MK25 has terrific air flow characteristics and lasts forever between rebuilds. IP drop on those is tiny. But you pay for these improvements with a more expensive rebuild kit, more crap to replace, and a few more places for a leak. And most divers would never ever notice a difference between the two. But it sure looks good on the test machines, which gives the salesmen more ammo for a good pitch.

In practice I agree with you in the sense that I end up using my MK5s 90% of the time, and if it weren't for my needing DIN on the doubles, probably I'd use them all the time. I'm giving occasional thought to replacing my perfectly good MK10s on the doubles with MK15s, mostly because I have a good supply of seats and bushings for the MK15, and it does handle HP pressure better than the MK10.

 

[Akimbo]

I don't see the benefits of super high flow rates of a piston if the flow rate of a diaphragm is still 5 times better than it needs to be in any practical diving application…

I have not seen numbers that indicate a diaphragm is 5x larger than needed at peak flow rates but your point is well taken. Remember your original question and the inability to accurately identify what “adequate” flow was when the piston was introduced.

 

[SubAquatix]

Interestingly enough, I've got a pair of SP MK 18's, which offer BOTH diaphragm 1st-stages AND rotating turrets for optimal hose routing. !

I have three myself with 250 HP's/V's. Why they stopped selling these in the US is beyond me as they were, arguably, the finest reg they ever made! I had one ScubaPro Engineer tell me he thought the reason distribution was pulled from the US was they were effecting Mk25 sales, although, nobody has ever verified that!

 

[halocline]

I have three myself with 250 HP's/V's. Why they stopped selling these in the US is beyond me as they were, arguably, the finest reg they ever made! I had one ScubaPro Engineer tell me he thought the reason distribution was pulled from the US was they were effecting Mk25 sales, although, nobody has ever verified that!

There might be some truth to that; the MK16 was effectively replaced by the MK17 (and later, unsealed MK11) and the MK16 was basically a MK18 without the turret. The MK17 did have a far improved seat arrangement, but SP techs were supposed to retrofit that into the MK16/18.

I wouldn't say they were the 'finest ever made'; IP stability over the supply range is nothing to write home about. But as with almost any decently designed and manufactured scuba reg, they work absolutely fine and there's no real-world difference between a dive with a MK18 and with a MK25.

 

[SubAquatix]

There might be some truth to that; the MK16 was effectively replaced by the MK17 (and later, unsealed MK11) and the MK16 was basically a MK18 without the turret. The MK17 did have a far improved seat arrangement, but SP techs were supposed to retrofit that into the MK16/18.

I wouldn't say they were the 'finest ever made'; IP stability over the supply range is nothing to write home about. But as with almost any decently designed and manufactured scuba reg, they work absolutely fine and there's no real-world difference between a dive with a MK18 and with a MK25.

Thus the word, arguably!! LOL while I concur on IP Stability, at 7-8 psi across service pressure, it has little to do with the total delivery of gas. My experience has been, in working dive to over 250fsw, on Trimix blends and under the ice, the MK18 regs have, consistently performed at or beyond, peer regs, based on comments and comparisons in the field.

Frankly, I am scared to replace them!!! LOL

 

[Curtis C]

I don’t think the question of why it was invented can ever be answered. I think we can question as to why they are still used.

I don’t know what the cost difference is in manufacturing, but could it be cheaper to manufacture piston regs? Low cost to make plus high flow rate which is good for marketing equals high profit margin for Scubapro?

My old Scubapro MK 14 diaphram reg has a rotating turret. On a side note it still is one of the best breathing regs I have ever dove.