Diaphram vs piston regs

[grasstrimmer]

As you can tell I am new to this.(Just taking my ow class). Can someone explain the difference between diaphram and piston regs. Why would you get one over the other.

 

[DA Aquamaster]

Piston regs come in two flavors:

1. Unbalanced "flow by" piston regulators - These are dirt simple with a bare minimum in terms of parts count and a maximum in terms of reliability and ease of service. Performance tends to be on the low end of the scale but current models like the Scubapro Mk 2 still offer more than enough performance for any recreational diving need. They are very durable due to having only one moving part and only two dynamic o-rings, both of which are in intermediate pressure areas in the regulator.

Performance in terms of raw flow rate is limited by the design as the orifice size itself is limited. If you increase the size of the orifice (where the high pressure air form the tank enters) in the regulator you increase the flow rate, but you also increase the drop in intermediate pressure as the tank pressure falls from full to empty. This then requires an increase in piston head diameter, and that becomes the limiting factor in terms of overall regulator size. Consequently, most unbalanced piston first stages have an IP drop from about 140 psi to 120 psi and that 20 psi difference can be felt at the second stage where the inhalation effort increased toward the end of the dive. This is the case as these first stages are usually paired with an inexpensive unbalanced second stage, where changes in Intermediate pressure (IP) affect inhalation effort. When paired with a balanced second stage, breathing performance will remain excellent.

2. Balanced Piston "flow thru" designs - These have traditionally been at the top of the heap in temrs of flow rate and respnse time and offer exceptional performance with a comparatively low parts count and simple design. The design is balanced in that the change in tank pressure has no effect on the intermediate pressure which then stays very stable through out the entire range of tank pressure. These are usually paired with more expensive balanced second stages, but if paired with unbalanced second stages, performance is still good as the IP is very stable and inhalation effort does not change. Some designs lately however have been becoming much more complex in terms of parts count and environmental sealing with the result that some are as complicated as many diaphragm designs.

Diaphragm first stages come in a single flavor - balanced:

Diaphragm designs are almost universally balanced as it is extremely simple to balance the seat carrier versus leaving it unbalanced. There are currently no unbalanced diaphragm first stages in production (and they have not been produced for at least 25 years).

The diaphragm design has traditionally been a bit more intensive in terms of complexity and parts count and they all incorporate a comparatively large flexible diaphragm. However as noted above, the difference in complexity has decreased compared to recent piston first stages.

Diaphragm designs have historically lagged in terms of flow rate and response time compared to balanced piston first stages, but this difference has at the same time become less, and less relevant. A modern diaphragm design will have a flow rate at or above 150 SCFM. This is still half the flow rate of a very high performance balanced first stage like the Scubapro MK 25 - but 150 SCFM is enough flow rate for any recreational, deep air or mixed gas technical diving so the extra 150 SCFM flow rate of the Mk 25 is essentially a waste as it will never be used in the real world.

Diaphragm first stages are often environmentally sealed (but contrary to popular belief not all diaphragm first stages are environmentally sealed) and some of them are sealed using silicone oil or alcohol and are a pain to maintain. The newest of the breed use a dry sealed chamber and are excellent cold water regulators.

Reliability in the real world is about the same and in short it does not matter if you buy a piston or diaphragm design - if you get a reg from a reliable, long established company that makes quality regs, you can't really go wrong.

Focus on the features you want in the second stage, whether or not you will be diving in cold water (below 50 degrees F) and buy a reg that you can get serviced locally - all of those are more important factors than the design itself.

 

[Poseidon8118]

Great explanation as always DA! Grasstrimmer I would recommend an unbalanced "flow by" piston regulator: its cheep, bulletproof, and will let you know when your tank is low on gas. The problem with new divers is that sometimes they forget to monitor their air. If your regulator becomes harder to breathe on at lower tank pressures; you will insure your safety underwater. As soon as you feel the difference in inhalation effort it should warn you to look at your spg and surface. Another thing is that they are inexpensive so if you don’t dive much you’re not out a lot of money. Later on you can upgrade if you find that you’re a diving addict and have acquire all the skills necessary to be an aware diver.

 

[Scuba.com]

Basically put, for the consumer, unless you have a need for a diaphragm 1st stage, it is a case of 6 in one hand, half a dozen in the other. They both do the same thing for you, and for any purposes you'll ever need, in the same way for the most part.

Get the features you find important in the regulator such as light weight second stage? Adjustable air flow? Life time warranty for parts? Moisture vains inside the second stage? Balanced first stage (for the cost, I personally won't buy one that's NOT any more)?

Enjoy!

 

[Hoosier]

Get the features you find important in the regulator such as light weight second stage? Adjustable air flow? Life time warranty for parts? Moisture vains inside the second stage? Balanced first stage (for the cost, I personally won't buy one that's NOT any more)?

Enjoy!

Agree 100%......

 

[djanni]

Piston regs come in two flavors:

1. Unbalanced "flow by" piston regulators - These are dirt simple with a bare minimum in terms of parts count and a maximum in terms of reliability and ease of service. Performance tends to be on the low end of the scale but current models like the Scubapro Mk 2 still offer more than enough performance for any recreational diving need. They are very durable due to having only one moving part and only two dynamic o-rings, both of which are in intermediate pressure areas in the regulator.

Performance in terms of raw flow rate is limited by the design as the orifice size itself is limited. If you increase the size of the orifice (where the high pressure air form the tank enters) in the regulator you increase the flow rate, but you also increase the drop in intermediate pressure as the tank pressure falls from full to empty. This then requires an increase in piston head diameter, and that becomes the limiting factor in terms of overall regulator size. Consequently, most unbalanced piston first stages have an IP drop from about 140 psi to 120 psi and that 20 psi difference can be felt at the second stage where the inhalation effort increased toward the end of the dive. This is the case as these first stages are usually paired with an inexpensive unbalanced second stage, where changes in Intermediate pressure (IP) affect inhalation effort. When paired with a balanced second stage, breathing performance will remain excellent.

2. Balanced Piston "flow thru" designs - These have traditionally been at the top of the heap in temrs of flow rate and respnse time and offer exceptional performance with a comparatively low parts count and simple design. The design is balanced in that the change in tank pressure has no effect on the intermediate pressure which then stays very stable through out the entire range of tank pressure. These are usually paired with more expensive balanced second stages, but if paired with unbalanced second stages, performance is still good as the IP is very stable and inhalation effort does not change. Some designs lately however have been becoming much more complex in terms of parts count and environmental sealing with the result that some are as complicated as many diaphragm designs.

Diaphragm first stages come in a single flavor - balanced:

Diaphragm designs are almost universally balanced as it is extremely simple to balance the seat carrier versus leaving it unbalanced. There are currently no unbalanced diaphragm first stages in production (and they have not been produced for at least 25 years).

The diaphragm design has traditionally been a bit more intensive in terms of complexity and parts count and they all incorporate a comparatively large flexible diaphragm. However as noted above, the difference in complexity has decreased compared to recent piston first stages.

Diaphragm designs have historically lagged in terms of flow rate and response time compared to balanced piston first stages, but this difference has at the same time become less, and less relevant. A modern diaphragm design will have a flow rate at or above 150 SCFM. This is still half the flow rate of a very high performance balanced first stage like the Scubapro MK 25 - but 150 SCFM is enough flow rate for any recreational, deep air or mixed gas technical diving so the extra 150 SCFM flow rate of the Mk 25 is essentially a waste as it will never be used in the real world.

Diaphragm first stages are often environmentally sealed (but contrary to popular belief not all diaphragm first stages are environmentally sealed) and some of them are sealed using silicone oil or alcohol and are a pain to maintain. The newest of the breed use a dry sealed chamber and are excellent cold water regulators.

Reliability in the real world is about the same and in short it does not matter if you buy a piston or diaphragm design - if you get a reg from a reliable, long established company that makes quality regs, you can't really go wrong.

Focus on the features you want in the second stage, whether or not you will be diving in cold water (below 50 degrees F) and buy a reg that you can get serviced locally - all of those are more important factors than the design itself.

Wow! You just sat down and wrote that.

I learned something.

Thx!