Piston or diaphragm 1st stage ?

[tbone1004]

so to follow up on what @lowwall said, the environment seals would keep water out of the spring chambers. Where you see the gap in the body is where you would have the seals.
On the pistons, where the water is, is replaced by lubricant and a band is applied around the holes to keep the lubricant in. It is messy and expensive to service contrary to anything you hear from anyone who is sucking on the Atomic teat, it is nothing more than a bandaid and not a real solution.
Dark blue is the grease, black is the rubber band to keep the lube in. The risk here is that if the lube is not done properly, water can get into the chamber and cause worse problems to the piston than if you had left it exposed. This happens, not often, but it does happen and a new piston is close to $100.

On the diaphragm, a second diaphragm is placed on top of the spring carrier
second diaphragm in dark blue, and the gray brackets are a metal cap that holds it in. Way better solution

Proponents of pistons will talk about how comparatively simple they are which is true, but more irritating to service since you have to shim them to set IP and it's generally irritating. They will also talk about how they can provide more gas than a diaphragm which is true for some though not really relevant since they all flow more gas than the valve is capable of supplying so does it really matter?

 

[GJC]

Hi everyone, I've been on a couple of dives but quite new to diving and am trying to teach my self more detail about gear before purchasing my own (and also cause I just like learning about it ).

I was more inclined towards a piston first stage to be honest however a source stated that piston 1st stages recieve water through them whilst they are working underwater while diaphragm ones do not. I dive only in sea water and was wondering if the salt would damage the components in the piston reg, therefore is a diaphragm more suitable for me as a diver who dives only in sea water ?



Thanks in advance. And apologies if question is funny or anything like that but your suggestions would really help

Unsealed piston regulators have an o ring that moves against a metal surface with each breath and it is exposed to the water you are diving in. If you dive in salt water and do not rinse well after diving, salt crystals form that can damage the o ring and the metal surface it rubs against. If you dive in water with silt or sand that is stirred up from the bottom, those particles can also cause damage. Sand and silt is very hard to rinse out because it tends to stick to any lube that is on the o ring or the metal surface it moves against. This is why some prefer diaphragm over piston regulators.

Some piston regulators do tend to perform slightly better than diaphragm regulators at very high flow rates or at depths beyond recreational depths so some tec divers prefer them.

Sealed regulators are preferred for ice/cold water and for those that just like the idea of not getting any water into the working parts of their regulator. Sealed pistons require more work and attention to detail when serviced. Sometimes, service techs inadvertently leave pockets of air in the sealing lube that can trap water in the reg. Sealed diaphragm regs usually have a sealed air pocket that is not filled with lube, so the sealing part is easier to service.

Oh, a bunch of posts appeared while I was typing that gives a lot more detail with pictures!

 

[RyanT]

On the pistons, where the water is, is replaced by lubricant and a band is applied around the holes to keep the lubricant in. It is messy and expensive to service contrary to anything you hear from anyone who is sucking on the Atomic teat,

My local Atomic tech sealed my regs. Perhaps this explains why I can't get him to service them now!

After taking the service course with @LandonL and seeing how diaphragm regs are designed (and serviced), I'm going to be moving all my regs to the Deep6. So yeah, 1 more vote for sealed diaphragms.

 

[StefinSB]

sealed pistons when sealed with grease a la Atomic are idiotic. Pain in the butt to clean for the techs, and expensive to pack because the cost of the grease is stupid. Scubapro engineered around it for cold water, Atomic couldn't be bothered. Remember also that these seals were done for cold water performance, not to keep them "clean", a sealed diaphragm is vastly superior for ease of maintenance.

It is obvious you don't like pistons since Atomic got bought by Huish. Regulators in general work, pistons or diaphragms. They work under water, salt or not. I also don't care if it's a "pain" for a tech to service my regulator. After all that's what the reg tech gets paid for. For the record, I also never screamed in pain when servicing my sealed pistons.

 

[herman]

I'll add a little to tbone, a damaged piston is the least of your worries. The piston will be at it's most extended (left in the above drawing) position when depressurized. If your tech did a poor packing job (or you did a poor job of rinsing a non-sealed piston reg) and salt water sets next to the piston, there will likely be corrosion on the reg body at the sealing surface of the piston oring. At best the reg will not work next time you use it and at worst the corrosion is so bad the body of the reg has to be replaced....not a cheap part and usually the first part the manuf stops selling. I have seen a bunch of ruined piston regs from this. I personally would not purchase a piston reg (Sherwoods are an exception) as my main reg. Don't get me wrong, I think unsealed piston regs are great, I own a bunch of them and love their simplicity, just as my first and only reg, I would not choose one. I suspect more dives have been made with them than any other reg but from a service stand point, a sealed diaphragm reg is unbeatable.

 

[Angelo Farina]

When I and my wife did buy our 4 regulators (in the seventies) there were not fully sealed first stages, either piston or diaphragms.
We did choose piston, the best available at the time: Scubapro MK5.
It was a good choice: those things are undestructible, we are still using them after 45 years...
The parts are all yet available and we managed to convert them to DIN and to make them oxygen compatible by mounting Viton O-rings and the MK10 conical seat.
However in 45 years the technology evolved and diaphragm regs improved their performances, to the point that nowadays they almost equalled a good piston, with significant advantages in terms of sealing.
Furthermore now a sealed diaphragm is significantly cheaper than an unsealed piston. Staying with Scubapro (the only brand which ensures 40 years of trouble-free operation and serviceability), a MK17 (sealed diaphragm) is just 188€, whilst a MK25 (unsealed piston) is 275€.
So I currently recommend the first one, either to a novice or to a skilled tech diver...

 

[Eric Sedletzky]

Unsealed pistons that are lubed well but not packed are OK, as long as you soak them then rinse the insides really well. To do this I always put the whole rig in the soak tub hooked up to a tank and pressurized. After soaking I stand it up and use a spray bottle set on jet stream and run water into the ambient holes to get any static salt water out.
It’s more time to clean for sure. Pistons need to be torn down and serviced more often because of the dynamic orings that are exposed to salt water. For this reason pistons might be better suited for DIY if service costs are a concern. I work on all my own now and get all the parts I need so I’m not worried about it. My first reg set was a Scubapro MK 20 bought new in 1998 and that has been my regular reg. I have several other too. I’ve dived it down to 42 degrees in salt water with no problems or freeze up.
If you are lazy about rinsing and or travel a lot where proper soak rinsing can be tricky then diaphragms are better. I own those too.
They are better for really cold water but I’ve never been in anything cold enough to worry about it.
Diaphragms have more parts, they depend on a rubber disc (the diaphragm) as the moving part which is also a membrane of sorts. They can fail and blow out, very rare but can happen. A former poster here (who is now banned from SB) posted a video once that he took of himself on a dive. The diaphragm on his 1st stage blew out at 160’ and the video showed all the drama. At least he had a bail out pony bottle.
The high pressure seats are more complicated on a diaphragm because they are usually attached to a metal stem rather than a nylon disc or biscuit like a piston has.
The actual diaphragm (the part) depending on quality can harden up and lose some of it’s flexibility restricting flow during high demand. High pressure seats can also begin to form cracks and break down. This is after years of no services though, but diaphragms can go years sometimes without service provided the insides are spanking clean.
I happen to believe that the quality of materials used in the consumable components of both types of regs is pretty important.
I’m suspect of cheap imported regs, most of which seem to be diaphragm style regs, not because of machining or design but because of the quality of materials used for critical components like seats, diaphragms, and stainless steel springs, etc.

 

[emoreira]

I've opened diaphragm first stages with lots of white deposits and rust in the internals. The origin of those is water coming in from second stages during rinsing that are "purged" or submerged first stages for hours with just the dust cap.
Even worst, if the water goes to the SPG, it will start to give wrong measurements.
Correct rinsing is paramount for the life of any regulator.

So, ok, diaphragm first stages keep water away from the internals during use, but do the user keep water away from the internals when rinsing ?

 

[rjack321]

I've opened diaphragm first stages with lots of white deposits and rust in the internals. The origin of those is water coming in from second stages during rinsing that are "purged" or submerged first stages for hours with just the dust cap.
Even worst, if the water goes to the SPG, it will start to give wrong measurements.
Correct rinsing is paramount for the life of any regulator.View attachment 683810
So, ok, diaphragm first stages keep water away from the internals during use, but do the user keep water away from the internals when rinsing ?

Bingo
Sealed is really a misnomer. Water is often getting into sealed regs. And in my experience the HP seats fail more often on diaphragms than pistons

 

[GJC]

I've opened diaphragm first stages with lots of white deposits and rust in the internals. The origin of those is water coming in from second stages during rinsing that are "purged" or submerged first stages for hours with just the dust cap.
Even worst, if the water goes to the SPG, it will start to give wrong measurements.
Correct rinsing is paramount for the life of any regulator.View attachment 683810
So, ok, diaphragm first stages keep water away from the internals during use, but do the user keep water away from the internals when rinsing ?

I suspect that the white deposits you see are aluminum oxide that comes from tanks that got moisture inside during fills. Rust would come from steel tanks exposed to moisture during fills. The filter in the first stage should filter out a lot of the dust, but if there is a lot of water in the tank the dust can be carried through the filter with water entering the first stage.

You don't see a lot of regulators made with steel or aluminum parts. Dried salt can show as white inside a regulator but the brass parts in regulators usually show green deposits after exposure to salt water.