Question re: diaphragm vs. piston first stage
- Thread starter concollective
- Start date
Please register or login
Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.
Benefits of registering include
- Ability to post and comment on topics and discussions.
- A Free photo gallery to share your dive photos with the world.
- You can make this box go away
Unique, no, the old US Diver Aquarius is an externally adjustable piston reg but in general piston regs are not externally adjustable where as diaphrams alway are.
Just to add to Tobin's comment the Scubapro MK20 could also be adjusted by adding or subtracting shims on the HP seat cap. Just to throw another wrench out there Sherwood redesigned their first stage a number of years ago where you were supposed to adjust your IP while under pressurs by spinnning the body cap and setting it with set screw on the side of the body.
I personally dive with MK25/G250 V my wife dives with Apeks TX50/DS4's and we dive in cold fresh water in Minnesota. The only time we have had problems with freezing MK20/25's was with our stage/deco bottles. The design and updates on that (MK20) first stage has been replaced to accomodate those problems.
The actual decsions on equipment purchase is really up to the ff:
1. What you can afford?
2. Who does / or who will be doing the servicing?
3. What you buddies dive with?
4. Access to parts
5. What you think of the "cool factor" with all the added features that everubody wants to sell you.
my 2 cents,
Jim
OP
concollective
Guest
Thanks to all of you for the helpful observations!!!!!
OP
concollective
Guest
Thalassamania - very interesting suggestion about the other brands I might check out. Can you tell me a bit more about why you like them better than Scubapro?
- Messages
- 22,171
- Reaction score
- 2,798
- # of dives
- 5000 - ∞
ScubaPro makes fine gear, I dislike their non-competitive marketing plan and what I feel is their yearly maintenance scheme that is little more than an additional profit center for the dive shop, if you have your regulator serviced every year (at might I add a somewhat higher price than it would cost to send it to say, Professional Scuba Repair, where someone who actually knows what they are doing and who has all the best tools will repair it (with parts) for less that the LDS will charge just for labor. ScubaPro top of the line gear is not better than other companies' top of the line gear, they just sell you smoke and mirrors to go with your regulator. And if you are at all mechanical (e.g, can you fix a leaky toilet?) HOG will let you take a class and buy parts and service your regulator yourself.
I used to dive with piston regs and used Mk 20's and Mk 25's for about a decade in very cold water technical diving before switching to Mk 17's.
I personally never had any issues with the Mk 20 or 25 freezing, but I had team mates who did on the same dives. My impression is (and remains) that the Mk 25 is not problematic if flawless cold water technique is used, but it can be problematic in water colder than about 45 degrees F if flawless technique is not used, particularly on deep dives with higher flow rates.
My switch to the Mk 17 was noteable as it was the first diaphragm reg I was both truly comfortable with and that I felt delivered fully adequate performance. During the transition/testing period I broke out my commercial diving gas block and used the same very finely tuned D400 second stage with both the Mk 17 and Mk 25 first stages at depth and could not detect any difference on the same dive literally from one breath to another on alternate first stages, nor could I detect any difference in bench testing with identical IPs on each reg.
----
In sandy/silty cave diving conditions, I have found the maintenance with the Mk 17 is much lower. With Mk 5 and 10 stage and deco regs, I have noted the need for more frequent service due to sand and silt getting into the ambient chamber and promoting wear on the piston head and piston stem o-rings. On the Mk 25 the piston head o-ring is a non issue as it uses 2 of them and the first acts as a scraper and essentially seals the second one from any dirt or salt - but the piston stem o-ring and the plastic o-ring bushings are still an issue.
----
It's implied in other posts but all piston regs and all diaphragm regs are not created equal within those classifications and there is as much variance within those groups as there is between those groups, so know exactly what you are buying and base it on your needs and the features of the reg, not just the basic piston versus diaphragm design.
---
Getting diver opinions of regulators is like getting infantryman opinions about their rifles/carbines. A large percentage of the time you will get an overall positive opinion because 1) it's what they have trained with and used successfully, 2) they have to have confidence in it and 3) 1 and 2 will cause them to overlook a lot of flaws, unless it has seriously let them down in a crunch. Given that most regs available today are pretty good number 3 comes into play only very rarely, so most divers will tell you they prefer their reg over most others just becuz it is what they are familiar with. So you have to take it all with a grain of salt.
I personally never had any issues with the Mk 20 or 25 freezing, but I had team mates who did on the same dives. My impression is (and remains) that the Mk 25 is not problematic if flawless cold water technique is used, but it can be problematic in water colder than about 45 degrees F if flawless technique is not used, particularly on deep dives with higher flow rates.
My switch to the Mk 17 was noteable as it was the first diaphragm reg I was both truly comfortable with and that I felt delivered fully adequate performance. During the transition/testing period I broke out my commercial diving gas block and used the same very finely tuned D400 second stage with both the Mk 17 and Mk 25 first stages at depth and could not detect any difference on the same dive literally from one breath to another on alternate first stages, nor could I detect any difference in bench testing with identical IPs on each reg.
----
In sandy/silty cave diving conditions, I have found the maintenance with the Mk 17 is much lower. With Mk 5 and 10 stage and deco regs, I have noted the need for more frequent service due to sand and silt getting into the ambient chamber and promoting wear on the piston head and piston stem o-rings. On the Mk 25 the piston head o-ring is a non issue as it uses 2 of them and the first acts as a scraper and essentially seals the second one from any dirt or salt - but the piston stem o-ring and the plastic o-ring bushings are still an issue.
----
It's implied in other posts but all piston regs and all diaphragm regs are not created equal within those classifications and there is as much variance within those groups as there is between those groups, so know exactly what you are buying and base it on your needs and the features of the reg, not just the basic piston versus diaphragm design.
---
Getting diver opinions of regulators is like getting infantryman opinions about their rifles/carbines. A large percentage of the time you will get an overall positive opinion because 1) it's what they have trained with and used successfully, 2) they have to have confidence in it and 3) 1 and 2 will cause them to overlook a lot of flaws, unless it has seriously let them down in a crunch. Given that most regs available today are pretty good number 3 comes into play only very rarely, so most divers will tell you they prefer their reg over most others just becuz it is what they are familiar with. So you have to take it all with a grain of salt.
Excellent post as always Larry; but you did not comment on the "snap to" effect. Is this just SP hype or can one actually differentiate the air delivery between a piston vs. a diaphragm first stage?
hudson
Contributor
The only two reasons I'd pick a (flow-through) piston reg over a diaphragm:
1) Concerns about reliability after flooding, with stages and sidemount tanks.
2) Not to add fuel to the fire, so to speak (O2)
1) Concerns about reliability after flooding, with stages and sidemount tanks.
2) Not to add fuel to the fire, so to speak (O2)
Very subjective in addition to the fact that the only balanced pistons I've ever used are MK-25's. The crisp popping action is probably due to the old school G250's that I have attached to them.
I have a number of zeagle 50D's and I do not like them. I will switch out the G250's and put them on the 50D's and vice-versa to see what happens.
-matt
Similar threads
