Air flow rate for 1st and 2nd stages

[AquaNSun]

I was wondering if anybody has estimations for the followings based on experience or access to technical data from manufacturers?

General air flow rates for 1st and 2nd stages (separately):

1) High end regulators
2) Mid end regulators
3) Entry level regulators

Another question to pick your brain

 

[islanduni]

Sometimes questions don't get answered around here. Buy a S600 with a G25. That's the best!

 

[tfsails]

Second opinion: Get a Zeagle 50D. They're the best.

Go to Scuba Lab; sometimes they have reg comparison charts that list flow rates. Not sure of the web address.

 

[Puffer Fish]

Here you go:

Regulators | Scuba Diving Magazine

A ton if information if you go back in history there.

 

[AquaNSun]

Thanks. Just to clarify a bit here - Im NOT looking for the best regulators. I'm interested to get a general idea/information as to what ranges air flow rates would be for each category. That's of course provided if somebody has that info compiled or experienced as a tech to have such info. Single data from one manufacturer wouldn't be very accurate. Groups of data compiled would be best. I know this is kinda hard to get, so Im just 'hoping' someone might have something as close as possible. I think this is interesting to know.

 

[Bubbletrubble]

I'm curious. Why are you interested in this info? Are you trying to figure out what the performance-cost trade-off is so that you could buy a relatively inexpensive second stage + first stage combo that still offers robust flow rates? If that's the case, I'd suggest that you look at other metrics/features beside flow rate. The fact of the matter is that, with the exception of maybe some very low-end regs, pretty much any first stage out there can deliver way more gas than you could ever possibly need. Whether the second stage "breathes like a dream," to a large extent, depends on whether the reg was tuned properly to the first stage i.p.

 

[AquaNSun]

Im just curious (and perhaps others might be interested as well). If somebody says "This is a high flow reg" but what's a high flow reg? If you have a number says 300 scfm, then it has some meaning. If I know an entry-level 1st stage would be in the range of about 80 scfm, that is meaningful to me. Im interested in a general range, not a specific reg, so for each category it would be different. Im not worry about not getting enough air flow. Like I said, Im not looking for the best reg, or trying to do a performance/cost analysis. Im just looking for some educational info and this question could lead into other discussions. I guess Im weird

 

[Bubbletrubble]

That's cool. Curiosity is fine. To my ears, though, "high flow reg" sounds suspiciously like marketing mumbo-jumbo. Maybe others will disagree.

Performance-wise, the highest required flow rate of a first stage is whatever two divers might need in an air-share at depth under conditions of stressed breathing. Some additional performance might also be included to accommodate simultaneous operation of a drysuit/BCD inflater. I don't know this number off the top of my head, but I'm sure that the SB community could estimate something.

Maybe a more useful list would be regs that meet or exceed that required flow rate vs. regs that aren't quite up to snuff. My guess is that pretty much every reg on the market passes the bar...but I don't know for sure.

Sorry I couldn't be more helpful...

 

[halocline]

I have some approximate figures for some SP 1st stages. Here you go:

MK2 100SCFM
M5 150SCFM
MK17 200SCFM
MK25 300SCFM

I'm going to take a reasonable guess at a few 2nd stages:
R190 (and similar models) 40SCFM
156/G250/S600 (barrel poppet with s-wing poppet) 60SCFM

The problem with using flow rates to evaluate reg performance (if that's what you're doing) is that all of these rates are far higher than the "in use" flow rate of a scuba tank valve, meaning one that's attached to a tank. Reg flow rates are measured on a machine that provides constant pressure at extremely high volume. Another issue is that all of these numbers are FAR higher than any of us could ever need at anything close to recreational depth. 100SCFM is the equivalent of emptying an AL80 in around 45 seconds.

You can infer some things from flow rates, I suppose. However, the MK25 has twice the flow rate of the MK5 and I challenge anyone to be able to tell the difference in diving performance between these two 1st stages with each attached to an identical 2nd stage. Some 2nd stages use strong venturi assist to increase flow capacities. This can result in huge amounts of air flow at impressively low WOB numbers, but in fact can feel un-natural while diving. A 2nd stage like the D400 might not have those kind of numbers, but has a very smooth and stable feel while diving.

 

[Greg Barlow]

First stage flow rates can vary from a low end of approximately 100cfm to the upper end of approximately 300cfm. The low end would typically be that of an unbalanced piston design, with the upper being a balanced piston with a larger than "average" piston bore diameter. Most of the balanced diaphragm designs will have a maximum flow rate between 130-200cfm.

Second stages will generally have flow rates ranging from 40-75cfm depending upon the size and design of the incoming gas orifice.

With that in mind, a first stage will display a certain amount of intermediate pressure drop while the second stage is releasing gas. For example, regulator X has an IP of 138psi while in the static mode. When you fully depress the purge control, the IP drops to 125psi. A reg with an unbalanced piston first stage might have an IP drop of 20psi, while a balanced piston design might only drop 8psi.

Now, to the real world...Regs are tested on supply lines that can maintain stable air pressures at much higher flow rates than what is possible with a cylinder valve. So...You have your "high performance" first stage that has an "advertised" flow rate of 300cfm. You place it on a cylinder valve that has no where near that flow potential. Interesting, huh?

Those who are skeptical of this line of reasoning should do this simple experiment. Take a cylinder of your choice and determine the volume of gas that it contains. Next, using a stop watch and ear plugs, open the valve fully. Record how long it takes for the cylinder to empty. You will quickly see that a first stage's flow potential cannot be met with the incoming supply pressure.

Me? I am perfectly content using first stages with a flow rate between 140-170cfm, and second stages delivering up to 50cfm.

Greg Barlow
Former Science Editor for Rodale's Scuba Diving Magazine