Piston vs Diaphram 1st stage

[GotAir]

I'm sorry to be such a Newbie but what is better overall. I dive deep and shallow but not in water below 50 degrees, it just dosnt get that cold here.

Mike

 

[jhelmuth]

I think most opinions will gravitate toward a balanced diaphram - but having said that, I'd advise that you simply tryout as many as you can and consider which breathes the best for you and weigh the pros/cons against the type of diving you will want to participate in.
For me - it was Scubapro MK25 w/ and S600 secondary (an over-balanced piston design). I only dive warm water and this baby breathes the same at 140 fsw as it does at 14 fsw. I love it. But I'd also tell you that I'd probably make a different choice if I had any inclination at all for diving colder water - like 45 degrees or colder (actually, anything below 60 degrees is COLD - to me!).

 

[jiveturkey]

I agree with jhelmuth. I have the same reg and it's great. If you're diving in a lot of silty water or if you do a lot of shore diving a diaphram might be better for you. No particles will get into the first stage with a diaphram. Then again, you can always get your piston reg environmentally sealed.

The good thing about a piston is that it's simple for your technician to service. Not to say that a capable tech would have a problem with a diaphram but I think it's easier to get a piston reg serviced.

 

[Charlie99]

This subject has been beat to death in multiple threads, such as http://www.scubaboard.com/showthread.php?t=1739&page=1

After all of the shouting is over, the consensus is that there are lots of good regs out there, both piston and diaphram.

 

[Munin]

The good thing about a piston is that it's simple for your technician to service. Not to say that a capable tech would have a problem with a diaphram but I think it's easier to get a piston reg serviced.

This is not true. A standard diaphragm reg such as a USD/Aqualung or Apeks is simpler and easier to work on than a good piston such as a Scubapro. I know - I was a service tech for a few years and have worked on almost everything made.

 

[jiveturkey]

This is not true. A standard diaphragm reg such as a USD/Aqualung or Apeks is simpler and easier to work on than a good piston such as a Scubapro. I know - I was a service tech for a few years and have worked on almost everything made.

I'm not a tech so I don't know. But I've always heard that piston regs have fewer parts and are simpler in design and are therefore easier to service.

 

[jhelmuth]

Munin,

I'm also not a tech (so I don't know either!). If you check with 20 techs, you'll find that they all have opinions and prejudices. Your's is valuable - but no better or worse than others (had you been a tech for 20+ years I might have had a different slant). I think it is fair to say that there are good designs in both diaphragm and piston types and that they are good to excellent choices. THe fact that one is easier to work on than another really shouldn't be much of a criteria for the user. I'd weigh much more in favor of a product for which there are many highly qualified techs as well as a history of avail parts (not my highest priority - but it would rank higher than wheather it was easier for you to service)

 

[Munin]

Munin,

I'm also not a tech (so I don't know either!). If you check with 20 techs, you'll find that they all have opinions and prejudices. Your's is valuable - but no better or worse than others (had you been a tech for 20+ years I might have had a different slant). I think it is fair to say that there are good designs in both diaphragm and piston types and that they are good to excellent choices. THe fact that one is easier to work on than another really shouldn't be much of a criteria for the user. I'd weigh much more in favor of a product for which there are many highly qualified techs as well as a history of avail parts (not my highest priority - but it would rank higher than wheather it was easier for you to service)

I agree with what you're saying entirely. Ease of service should not be a factor in choosing a reg for your average user since they are not the one servicing it, and for the type that does their own such as myself I would choose based on in-water performance rather than the time it takes to service. I use both Apeks diaphragm and SP piston regs on nearly every dive I do and am quite satisfied with the performance and reliability of each. My personal opinion of some of the other manufacturers is not really relevant since this was about diaphragm vs. piston regs, not brands. I did not mean to say that one style or brand was any better than the other.

What I was saying is that servicing most diaphragm regs is, for me, much easier and faster than doing a piston for a number of reasons. I am sure you can find somebody to disagree, but with the six years I worked on regs I am convinced of my position. Due to the area I worked in I dealt with a high volume repair business - at the busiest I could do a half dozen USD regs before lunch. That output is hard to match with the pistons I have experience with. 98% of the time diaphragms would work perfectly on the first try and the design is simply more efficient to service for a number of reasons. To me, pistons are not necessarily more complicated but are simply more time consuming. The difference is actually minor, it might be something like 10 minutes per reg, but having done the number of regs I have I must disagree with anybody that says it is easier to do a piston. This is, of course, entirely general since there are so many different designs out there, but it applies to a good number of regs. The exception I would make with pistons is Sherwood, which is about comparable to a USD in service time.

 

[mmcdds]

I agree that ease of servicing shouldn't necessarily be a factor to a diver that isn't going to service his own reg. As long as you can get the reg of your choice reliably serviced in your area, then I would choose the one that breathes the best for you. I like Apeks regs, I also like the the AquaLung Legend series. I think they're great breathing regs and they both happern to be diaphram regs, but there are a lot of SP fans on these boards that will say the same about their regs and theirs happen to be pistons.

 

[DA Aquamaster]

From a raw performace standpoint, balanced piston designs tend to have higher flow rates. For example an unbalanced piston first stage will provide a maximum of about 50 cu ft per minute, a balanced piston will do about 80 cu ft per minute, a compact Mk 10 style balanced piston design will do around 150 and the enlarged MK 20/25 style balanced piston design will produce nearly 300 cu ft/min.

The big advantage with balanced piston regs is that there is generally more room for the air to flow past the hard and soft seating surfaces than in an unbalanced piston or balanced diaphragm design. Personally I think 100 cu ft min is plenty for any conceivable situation and 300 cu ft per minurte is serious overkill. But the 100 cu ft/min mark limits the choices to a VERY good balanced diaphragm reg or to a balanced piston reg.

Form an ease of servie standpoint, an unbalanced piston s super simple with 1 moving part and 2 low pressure dynamic o-rings. Truly bullet proof and idiot proof. A balanced piston design like the MK 10 is also quite simple with one moving part, 1 llow pressure dynamic o-ring and 1 high pressure dynamic o-ring. A "modern" balanced piston design like the Mk 20/25 uses a bushing system to create tighter tolerances and eliminate the potential for o-ring pinch at higher service pressures. They are a little more complicated by still not what I would call hard to service and comparabel to a balanced diaphragm reg. Some dry balanced piston designs can get more complicated with another dry chamber, a check valve and a shraeder valve.

The one potential disadvantage of the piston reg is that intermediate pressure is normally adjusted with shims inside the reg. This is however not an issue in normal servide as you just put back in what you took out and it's fine, or altrnatively, you check the IP before you start and remove shims if you want to end up with a reg with a lower IP when you are done (about 5 psi per shim) The exception to this is the MK 25 which offers an external IP adjustment very much liek the IP adjustment found on most diaphragm regs. oi