Balanced piston vs diaphram first stage

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Which first stage is better? Is one better for recreational diving and the other better for tech/deep diving? Thanks for the help.
 
a diaphragm creates a barrier that keeps crap out of the inside of the reg,
and chances for internal corrosion are nil.

in a piston reg, you can get crap into the chamber and can damage the o-ring
and reduce performance or damage the regulator.

on the other hand, piston regs have fewer parts, which cost less and are easier
to work on and easier to service.

diaphragms have more parts and need more work. on the other hand, you can
neglect these more, since the chances for internal corrosion are much lesser.

pistons deliver a lot more air (or can, anyway). but then again, both can
deliver much more than you need.

on the other hand, for use in cold or dirty water, the diaphragm is much better,
out of the box.

so....

:wink:

[oooooh... here's an oldie but a goodie: http://www.scubaboard.com/showthread.php?t=1739]
 
Pretty well said H2Andy.

I'll add that a first stage has the primary job of sensing interstage pressure drop, then quickly reacting by opening the valve to replenish it. Diaphragm regulators can cycle (open & close) faster than piston regulators due to less mass and energy required in their mechanism to accomplish this task.

There are many top regulators of both first stage styles. So the "which is better" question remains unanswerable.

Anyway, I believe the second stage is far more important in determining the performance of a regulator.

We just paired out balanced second stage with two new simple first stages and they really crank! (Resort & Razor regulators.)

Chad
FL Zeagle Rep.
 
I agree, if you check all the old threads on the subject (as I did when I was lloking at regs) you'll find that no conclusion is reached. A good reg is a good reg and there are good regs of both designs. Look at the reports on the quality of the individual reg rather than the type of 1st stage.

A
 
I'm partial to piston regs just because they are so simple but the diaphram regs are easier to seal for cold water. You can't really go wrong with either one if you buy a good quality reg. I'm partial to Apeks, Atomic, Scuba Pro and Aqua Lung. I would by a balanced piston or a balance diaphram. I would not buy an unbalanced regulator.
 
A diapgragm versus piston design is not neccesarily better than the other for rec or tech diving

Diaphragm designs are often regarded as being sealed - and therefore more freeze resistant in cold water - but that is not always the case and some unsealed pistons designs are very freeze resistant. The Scubapro Mk 2 is a good example of a very reliable yet unsealed piston design that does extremely well even in 33 degree water.

Many divers almost automatically assume that all diaphragm designs are sealed when in fact many diaphragm first stage designs are not sealed. Many diaphragm first stage designs also come in both sealed and unsealed versions. Aqualung first stages are a good example as many come in unsealed normal versions as well as sealed "Supreme" versions.

And like some piston designs, some unsealed diaphragm designs are very freeze resistant. The Scubapro Mk 16 is a good example of an excellent unsealed cold water diaphragm reg. At the same time some sealed designs may freeze very readily if the seal over the ambient chamber leaks and floods or if the alcohol or silicone oil inside leaks out. So one factor in selection - cold water freeze resistance - really needs to be considered separately from piston/diaphragm design.

Generally piston designs tend to be comparatively simpler with few moving parts and generally less complicated design. Piston designs can be found in balanced models which are capable of very high performance as well as in very simple unbalanced models.

The advantage of an unbalanced piston designs like the Scubapro Mk 2 or Aqualung Calypso are extreme simplicity and reliability combined with minimal spaces in the regulator exposed to high pressure air. In these designs, there are only 2 dynamic (moving) o-rings and neither is exposed to pressure differences greater than 145 psi. The downsides are that these "flow by" designs have comparatively low flow rates around 80-90 SCFM and the intermediate pressure will decrease as tank pressure decreases leading to slightly higher inhalation efforts at low tank pressures.

High performance piston designs like the Scubapro Mk 25 have extremely high flow rates - around 300 SCFM in the case of the Mk 25. But they have slightly higher parts counts and one of the two dynamic o-rings in the balanced "flow through" piston design will be exposed to full tank pressure. This can create issues with high pressure o-ring "pinch" at high service pressures (over 232 bar / 3400 psi) and requires very close manufacturing tolerances to avoid the problem.

It's almost impossible to find an unbalanced diaphragm design as it is extremely simple to balance the seat carrier in a balanced design - so simple that it is almost impossible to justify not balancing it.

While piston designs use a down stream seat design where tank pressure helps open the valve, diaphragm designs use an upstream design where tank pressure helps keep the valve closed. This has theoretical implications should the mainspring in the first stage break as a piston design would posisbly continue flowing gas (most likely freeflowing it) while a diaphragm design would be more likely to stop providing any gas at all. But practically speaking, mainsprings in first stages are very heavy, very durable and breakage is all but totally unheard of.

Diaphragm designs tend to be slighlty more complex overall than balanced piston designs and tend to be a bit more difficult to service due to the higher parts count and the greater diversity in layout and design that is possible (compared to only two common types of piston first stage designs).

They also tend to fall between unbalanced piston and balanced piston designs in terms of performance with flow rates around 125-180 SCFM. However it needs to be stressed that anything over 110-125 SCFM is gravy anyway, even in deep air and technical mixed gas applications. So the 300 SCFM produced by a very high performance balanced piston design like the MK 25 is essentially overkill and is much like taking a Callaway Corvette to the grocery store.

Basically, if you buy a reg from a major company like Scubapro or Aqualung, it's pretty hard to go wrong regardless of the design and regardless of your rec or tech ambitions. In many cases, selection is often based on hose routing options and preferences as well as what you can get serviced locally.

Personally I am a big fan of the Scubapro Mk 17 and prefer it to the Mk 25 due to it's sealed design and exceptional cold water performance. The G250, X650, S555 or S600 second stages are all good choices for it.

I also have nice things to say about the Aqualung Legend first stage. It is well designed and has very good cold water performance. Aqualung's adjustable second stages are also well done and use an interesting poppet/shuttle valve design that seems to combine old and new technology to produce a second stage that performs nearly as well as a G250 or S600.

Since both the Mk 17 and Legend are diaphragm designs, I am obviously currently biased toward diaphragm first stage designs - which is very interesting considering that I have been a confirmed balanced piston first stage fan for the previous 20 years. I think that says a lot about the quality and performance of recent diaphragm designs as well as a lot about a general plateau and even regression in cold water reliability that seems to have occurred among current balanced piston designs.
__________________
 
Personally, I would rather pull maintenance on a US Divers SEA diaphragm type first stage than a Scubapro MK 20 piston stage. Some low end piston regs are fairly simple but a lot has changed since 1971 when a Scubapro MK5 balanced, flow through piston reg could be disassembled in a couple minutes with only one spanner and a wrench. The main selling point was that they were simple. Not so today, with the descendant, the MK20 being a clusterflop of plastic parts requiring several special tools to disassemble. What have they produced other than complexity? Stories persist about these expensive SP piston regs freezing up. In fact, after 30 years, the only improvement that I've seen on SP first stages is the change over to hypalon O rings. These helped transform the once notorious SP piston leakers into a fairly reliable regulator. Nowadays, most problems seem to occur after "service". If you want to blow your mind, try counting the parts in a piston reg. Get out the manual and look. I see no "simplicity" claim to be made for most piston regs.
 
DA Aquamaster -- any comments on the how well the envirionmental seal kits work on balanced piston regs?

As I understand it, the seal on my Atomics B1 isn't much more than a bunch of Christolube jammed into the ambient pressure port, and held in place with a rubber cover. Any problems other than the expense of repacking with Christolube with each service?
 
It's just a messy job is all. It makes it harder to clean them before you reassemble them.
 
Charlie99:
DA Aquamaster -- any comments on the how well the envirionmental seal kits work on balanced piston regs?

As I understand it, the seal on my Atomics B1 isn't much more than a bunch of Christolube jammed into the ambient pressure port, and held in place with a rubber cover. Any problems other than the expense of repacking with Christolube with each service?
Scubapro used their SPEC system prior to moving to the TIS system. SPEC (Silicone Protected Environmental Chamber) was messy to service but it was effective if properly maintained. The early SPEC regs (indroduced on the MK 3, Mk 5 and Mk 10) did not use a boot - just 1/16" holes in the ambient chamber and fairly thick silicone grease to prevent much leakage. Later SPEC equipped models (MK 10, Mk 15 and very early Mk 20's used a stiff rubber boot seated in a groove to hold the silicone in. The late Mk 15/Mk 20 boot was by far the best with a much wider boot that allowed for normal exapansion of the silicone and substantially reduced the amount of silicone lost over the dive season.

SPEC maintenence was not a problem for the occassonal diver, but if you dove a lot, you could find yourself needing to repack the ambient chamber mid season. If not, the voids in the chamber could become large enough to creater space for water to enter, freeze and cause the reg to freeflow. Packing was also a bit of an art to get it to happen with no voids in the first place. This was very hard to acheive on the Mk 10 due to how the piston sat in the reg body, but was much easier on the Mk 15 and Mk 20 givne that the piston head was in the swivel cap, not the body. Of course, in one of life's ironies as soon as SP got it perfected, they switched to the TIS system.

Personally, I liked the late model spec boots on the Mk 15's and early Mk 20's as they were very reliable, easy to pack and easy to maintain. However SP went with the silicone free TIS system to reduce the possibility of cross contamination on the bench once christolube came into use to accommodate 02 compatibility. This avoided the fairly high cost of packing with christolube, but was not as effective as a christolube packed ambient chamber would have been on a high performance reg like the Mk 20 and Mk 25.

In this regard, the Atomic approach of using a christolube filled ambient chamber is a more traditional, more conservative and more effective approach. The TIS system is adequate on the Mk 2, Mk 16 etc, but indaequate on the Mk 25 and the occurrence of freeze flows with the Mk 25 has seriously hurt the reputation of the Mk and Scubapro). So basically, you are in good shape with Atomic's system.

In general the use of silicone grease tends to be a bit more reliable than the silicone oil or alcohol used in many sealed diaphragm designs as if the diaphragm unseats or is punctured, the oil/alcohol leaks out, water enters and a freeze up is virtually guarenteed in cold water as water/heat transfer in and out of the ambient chamber is virtually nil.

Some sealed diaphragm designs are however dry designs. The Mk 17 for example uses a dry ambient chamber, a pressure transfer pad and a diaphragm with enough range of travel to avoid the need for a filler material to tranfser pressure. They are still vulnerable to water entry if the diaphragm is punctured, but they do not have the problem of the alcohol or oil in the ambient chamber expanding in high temperatures and unseating or rupturing the diaphragm and then leaking out. So it is a relatively simple and reliable design.
 
https://www.shearwater.com/products/swift/

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