Balanced vs Piston regs and why the big fan arguments

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flspy

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Can anyone explain- logically- what the big advantages are for piston vs diaphragm regulators, and is there a way to tell one from the other just by looking?

People seem to be very emotional on the subject- like Glock vs 1911.

If there is a good video out there i would love to see it.

Chris
 
The difference is design. Are there any big advantages? IMO there are some advantages to both styles. but both may have the same features and performance.


One way that they generally differ is the balance chamber. Diaphragm regulators balance at one end(opposite from the seat), piston regulators balance in the middle(between the piston and seat). Knowing where they balance will help you identify them by looking. You may notice most piston regulators allow water to enter through holes in the side of the regulator while diaphragm regulators allow the water to enter at one end.
 
After you've looked at a couple you can usually ID them pretty quickly, look at Scubapro*with exception of Mk17 and a handful of others* or Atomic's lineup and compare it to say Apeks/Poseidon for a good comparison.

Pro's/Con's
Diaphragms used to have a significantly lower air flow which caused piston's to be preferred for a while, but Diaphragms are not flowing more air than the valve can provide, so this is a nonissue and anyone that brings it up is reading 30 year old data and assuming technology hasn't changed. Airflow is essentially irrelevant at this point, any modern production regulator can flow more air than you could ever use.

Pistons are a simpler design and used to be cheaper to make. Again, at this point technology has caught up and they are about the same price point for comparable designs. Apeks DST vs. Scubapro MK25 for example.

Diaphragms are easier to seal thus generally better suited for dirty/muddy water conditions i.e. sump diving, and ice diving. Pistons can be sealed but it requires packing the chamber with grease which is messy and expensive causing service cost to increase *can be around $50 or more per first stage at service for the grease and extra cost for cleaning in the ultrasonic*. Sealed diaphragms are by far and large the preferred regulator for ice diving and nasty sump diving. Also nice for salt water since you can just rinse them off and there is no salt on the internals. Unsealed pistons require quite a bit of soaking to really get all of the salt out, as do unsealed diaphragms which imho are actually worse for salt water/cleaning than pistons because the caps can be a pain to clean out.

Balancing is one of the important aspects in CCR diving for some applications that require constant IP and sealed diaphragms due to the balancing mechanism are generally "over balanced" which means IP goes up as tank pressure goes down. This is the opposite of an unbalanced regulators trend, but it can cause problems in the volumetric flow of gas through the orifices and is a problem for some rebreathers. This is why you generally see unsealed diaphragms on certain CCR's. Poseidon has gotten around the sealing problem with their new MK3 and it's properly brilliant.

O2 use, pistons tend to hold up better to 100% O2 where you'll usually see some burn marks on the diaphragms. Not a big deal and don't know of any that have actually failed because of it, but you can get away with a bit longer of a service interval with pistons in general. Many still use diaphragms on their O2 bottles, but if I were choosing a dedicated O2 reg it would be a piston.

Size, most pistons can be made smaller than their diaphragm cousins. Poseidon has a small Mk3 for O2 bottle use that is one of the few exceptions to the rule, but if you look at something like the Scubapro MK2 or the Sherwood regulators they are super small, and diaphragms are generally a bit larger. I don't know of any diaphragms other than a couple from Poseidon that have the valve orifice on the bottom of the regulator, they generally come in from the side which makes them a bit bigger. This small design is nice for things like O2 bottles, CCR bailout, etc where you need as small of a profile as possible and the diaphragms stick out a bit too far.

Last for me is ease of adjustment for service. Up until the MK25 from Scubapro, most pistons required shimming the piston to change the IP where diaphragms are done by adjusting a screw with an allen key at the top. Super easy and convenient.
 
I firmly believe that the diaphragms are a superior design for every day applications and you will never see me purchase a piston regulator for backgas or stage bottle use, but I do have them for deco bottles due to their size and durability in high PO2 environments, they were also like $60 new from Piranha, so can't argue there... No advantages to a piston for normal use though, just added expense at service for sealing them, or added time cleaning them after diving.
 
How can you even compare holding a 2x4 with holding a solid piece of metal :) I like 226 though :)

On the regulator side though, I prefer the pistons for the stage and deco tanks because if you screw up and have the reg flooded the piston is easier to rebuild.

For back gas though I would take diaphragms , they are better in cold water too as they are sealed by design. But I do have experience diving my MK5 and MK15 in 37F water.



Can anyone explain- logically- what the big advantages are for piston vs diaphragm regulators, and is there a way to tell one from the other just by looking?

People seem to be very emotional on the subject- like Glock vs 1911.

If there is a good video out there i would love to see it.

Chris
 
https://www.shearwater.com/products/perdix-ai/

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