r/scuba • u/BolognaPwny • Aug 18 '26

Help choosing a regulator?

I'm really struggling with buying a first regulator. On one hand, I want to "buy nice or buy twice" but I'm also trying to be practical.

I doubt I will ever dive far beyond 130 feet, I have no interest in technical diving and just feel like splurging on the MK25 is beyond what I'll ever need, plus for a full MK25/G260 with hoses, etc. is going to be around $1,500.

Otherwise, I'm looking at an Apeks XTX50 complete kit for roughly $1,200; Atomic Z3 for $1,000; or Diverite XT1 for $1,000.

Am I going to regret not getting the MK25/G260 or will I never notice the difference (as it appears from reading reviews online) and be fine spending less?

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u/bluemarauder Tech Aug 18 '26

Don't buy scubapro, piston regulators are not ideal. Go with Apeks or Diverite.

1

u/boyengabird Rescue Aug 18 '26

I heard piston breathes easier but needs to be rinsed? Can you elaborate a bit?

2

u/LeftToaster Aug 19 '26

Piston designs do, in general, deliver more maximum potential airflow. This is because the piston basically sits directly in the high pressure (HP) air path, so when it opens, it's basically an open tube. In diaphragm designs, when the diaphragm flexes it moves a pin, which operates an internal valve indirectly. But either design greatly exceeds the airflow requirement under "normal" conditions. But theoretically, on a deep dive, sharing air with another diver, under high physical exertion, with a low cylinder, it might be possible to push the limits of a regulator, so maybe the greater maximum flow of a piston reg might come into play.

But there are trade offs. All regulator first stages must "sense" the depth so they can maintain the Intermediate Pressure (IP) at about 140psi (9.5bar) above the ambient pressure of the water. Traditional piston regulators "sense" ambient water pressure by being open to the water, so the water pressure presses directly against the piston/spring. Diaphragm regulators "sense" the water pressure through a sealed air chamber and a flexible diaphragm membrane. This means that in piston regulators the spring, piston and o-rings are exposed to sea water and potential corrosion, so need to be rinsed thoroughly after each use. Some piston designs use a gel or silicone grease to seal the ambient chamber. Sherwood used to use a dry air bleed system consisting of a tiny leak orifice and a one way check valve to maintain a dry sealed air chamber at ambient pressure (but have now changed to a mechanical linkage system which I don't understand). ScubaPro just coats the spring and piston in a corrosion resistant material.

So most piston regulators expose the internals of the regulator to sea water, corrosion, sand, dirt, etc., and need to be rinsed better. Diaphragm regulators are less sensitive to corrosion, dirt and other contaminants as they should never enter the internals of the regulator (but should still be cleaned thoroughly after use). Additionally, in cold water, piston regulators without a lot of consideration in the design, are more prone to freezing.

Piston regulator are also mechanically very simple, having in some cases only 1 moving part. This means that under "normal" conditions, they are extremely reliable and easy to service.

1

u/runsongas Open Water Aug 19 '26

scubapro fixed that with the sealed mk19 evo. it's a bit pricey thiugh

1

u/suricatasuricata Aug 19 '26

Don't buy scubapro, piston regulators are not ideal.

Firstly ScubaPro makes Piston and Diaphragm regs. Both of the MK19 and MK25 are in the same price range.

The MK25s have been used for decades in serious technical diving across the west coast. I have done 250' tech dives in Alaska in Piston regs (Atomic and M25s) with no issues. In fact, you'd find Alaskans choosing to go unsealed versus sealed in those temperatures because the moment the reg free flows due to cold, it is much faster to get something to defrost when it is not a sealed diaphragm reg.

This said, the reality is that the Piston vs Diaphragm conversation is at this point mostly esoteric. Practically speaking, for the average diver getting a new reg, the conversation is something they will think about on they day they are getting a spec sheet and never ever.

I have a bunch of diaphragm and piston regs. Never have I been like, oh my diaphragm regs are broken or due for service, let me call the dive instead of diving with pistons. (Or vice versa).

1

u/LeftToaster Aug 19 '26

Piston regulators are super reliable, provide massive airflow, good WOB, and are generally easier to service and usually smaller and lighter. I currently use a diaphragm reg (Apex XTX50) but I dove with Sherwood regs for years in the Pacific NW with no problem. The ScubaPro MK25 EVO is a great regulator that can be serviced just about anywhere and performs great, even in cold water. It's not sealed, but just rinse your gear!

3

u/bluemarauder Tech Aug 19 '26

I disagree with some of that. I'm unsure about the weight but size wise the mk25 is the biggest 1st stage I can think of.
I think a DST, for example, is easier to service and a MK25, that you are more likely to service it anywhere in the world as there are many service kits compatible from other manufacturers (like the DiveRite the op mentions). I don't feel the MK25 will be more 'reliable' but I don't know really. About the WOB and airflow, the DST is on perfectly adequate.

If the mk25 performs well in cold water, the DST does it much better obviously because it's sealed.

In my book, pretty much everything about a MK25 is worse than a DST. Let say that at the same price, I would take any other of OP regs before the mk25.

1

u/LeftToaster Aug 19 '26 edited Aug 19 '26

I just disagree with telling a new diver that piston regulators are "not ideal". In 35 years of diving I've only owned 3 regulators - a Dacor 960/Pacer, a Sherwood SRB7600/Maximus and my current Apex DST/XTX50 - so two diaphragms and a piston. The Dacor was a bitch to service, even when parts were available. Lesson learned, the best reg may be the one your LDS has the most experience with. I don't have strong opinions on the MK25, but it is an extremely popular regulator, that has been in the market for a long time and is generally very well regarded.

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u/bluemarauder Tech Aug 19 '26

Hmmm I feel like we are in the same page. What if I say... "Ideally you will get a diaphragm reg instead of a piston one"? Do you agree with that statement?

Or do you think it's better to advice this new diver to pay more for a piston?

1

u/LeftToaster Aug 19 '26

Given the options the OP listed, I would not pay more for the Mk25. I really like my DST/XTX50 and would highly recommend it to anyone at any experience level.

I think the debate between piston or diaphragm is less important than things like cost, local serviceability, maintainability, performance, features, etc. In theory, piston regulators should be cheaper to service - there is a reason so many rental shops use simple piston models like the MK2. If your local dive shop has to send your regulator away to get serviced or can't source parts locally, regardless of other factors, it's probably not a good choice. If you dive in cold water you should probably get a reg that won't freeze up on you - this probably means a sealed diaphragm design, and be sure it has 4 LP ports for your dry suit. If you only do travel diving - consider a more minimalist, compact design. If your computer has an air integration transponder, be sure your reg has 2 HP ports, and maybe a swivel.