what is the flow rate of tank valve

[rstofer]

The solution would be to find a submersible IP gauge and head down to the recreational limit. Then hook up 2 divers and see how it works out. Numbers don't mean nearly as much as a good functional test.

Richard

 

[Bubbletrubble]

Ok so outside of physical attributes of port placement, special features, cost and ease of repair etc, it sounds like the biggest factor of performance is not air flow per say but more if the ability to maintain constant IP under demand

Is there anyway to quantatively check this. The reality of actually checking this via LDS is not very realistic. 1st a pool is nothing like being 40'-60' down. 2nd I've found the LDS tends to be biased towards their highest end line.

For starters, you can purchase an IP gauge. Hook it up to whatever reg setup you're testing and watch the needle as you take different kinds of breaths off of the second stage. Is the IP within the acceptable range of manufacturer specs? How quickly does the IP recover after taking a breath? Does the IP drift up substantially over time? I suspect that any properly assembled/tuned reg should give decent results.

Quite frankly, if you want to learn how to evaluate reg performance, you really need to learn more about reg design, assembly/disassembly, and how to tune a reg properly. I don't have as much experience as some of the other reg techs here on SB, but I'd venture a guess that the vast majority of crappy regs that I've encountered breathed poorly because they were improperly tuned or in desperate need of overhaul.

I like rstofer's idea of a functional test with air-sharing while using a submersible IP guage.

 

[halocline]

Ok so outside of physical attributes of port placement, special features, cost and ease of repair etc, it sounds like the biggest factor of performance is not air flow per say but more if the ability to maintain constant IP under demand

Is there anyway to quantatively check this. The reality of actually checking this via LDS is not very realistic. 1st a pool is nothing like being 40'-60' down. 2nd I've found the LDS tends to be biased towards their highest end line.

IP drop and recovery does seem to be a good indicator of 1st stage performance, although measuring it is not always easy. Here's an example:

A while back I compared the IP drop on my MK15, MK10, MK5, and a MK2, same 2nd stage, same IP gauge. The MK15 dropped the most under full purge, and this was very surprising to me, because the MK15 is a much higher flow reg than the MK2 or even MK5. What was even more confusing was that the MK10 also dropped a little more than the MK5 or MK2. The MK10 is higher flow than either of those. This would indicate that the MK2 had higher flow than any of the others; because in a closed system in which the 2nd stage is the limiting factor, higher pressure in the line should equal higher flow. Eventually I got smart and connected two 2nd stages, both balanced/adjustables. (They have very aggressive purges) Under full purge with both 2nds, the MK15 dropped initially the most, but within a fraction of a second stabilized at a significantly higher IP than the other regs.

I was still curious about the behavior of the IP gauge with one 2nd stage, and started a thread about IP drop as a performance indicator. I even called Peter Wolfinger, who was running scubatools at the time and wrote the book "reg savvy." I figured if anyone would know, it would be him. Nope....

Eventually I guessed that there are some venturi effects in the turret that can cause funny things to happen with pressure at different points. I was checking IP with a gauge on the LP inflator hose. If I had a direct in-line IP gauge that could be mounted at the 2nd stage connection the results might have been different, who knows.

Despite this, it is easy to get a general idea of how the reg is working with a simple IP gauge check; tap the purge, take a few breaths, try a few full purges, and do this enough times and you'll get a pretty good idea of how the 1st stage is functioning.

 

[herman]

Ok so outside of physical attributes of port placement, special features, cost and ease of repair etc, it sounds like the biggest factor of performance is not air flow per say but more if the ability to maintain constant IP under demand

Is there anyway to quantatively check this. The reality of actually checking this via LDS is not very realistic. 1st a pool is nothing like being 40'-60' down. 2nd I've found the LDS tends to be biased towards their highest end line.

First off, there is no need to do this at depth. The only difference between the surface and 100ft is the density of the gas will be somewhat greater which will decrease the flow a little but the difference is not going to be enough to measure with simple equipment. It's going to take lab grade equipment and in any case it will be nothing a diver could determine.
If you still want to do a comparison type test, you could connect 1 or 2 LP ports to simple valves and a IP gauge to another one. Then start opening the valve(s) slowly until your IP drops to some chosen value....15 psi might be a good starting point... and record the degrees of opening the valve required. The more the valve(s) has to be opened, the greater flow the reg is capable of. To be anywhere near useful, your gas supply will have to be large and capable of supplying a lot of gas at a constant pressure. This is going to be your biggest problem unless you have access to a set of banked tanks with a large flow capacity and a high flow HP regulator, not something very common for a home shop.....and ear plugs, this is going to be noisy.

With all that said, unless you are just curious it's pretty much a mute point. The second stage is still the most restrictive component in the assembly and pretty much any balanced second stage will cover up for any excessive IP drop. It's fun to experiment, love to do it myself but if your goal it to pick a "good" regulator it's a lot of effort for little gain.

 

[mictrik]

IP drop and recovery does seem to be a good indicator of 1st stage performance, although measuring it is not always easy. Here's an example:

What was even more confusing was that the MK10 also dropped a little more than the MK5 or MK2. The MK10 is higher flow than either of those.

I unfortunately threw out most of my scubapro literature from the late 80's. However I do remember them selling both the Mk5 and Mk10 at the time and I clearly remember the MK-5 having a slightly higher flow rate at 2000 PSI but a substantially lower flow rate at 300 or 500 PSI. The "advantage" to the MK10 was/is stability throughout the tank pressure range. I believe that they now measure the flow rates differently because if i recall at 2000 PSI the MK10 was stated to flow 79CFM while the MK5 was in the 80's. Todays MK-25 is said to flow 300cfm, I think that differential is too large so my bet is that the test conditions may be different.

Now if you were using a J-valve without an SPG and non-balanced second stage I would think that one should choose the mk-5 as it will be more sensitive to the J-valves spring restriction thus producing a reduction in beathing performance sooner indicating time to flip the J-reserve and ascend. With the MK10 the diver may not notice the pressure was down until you could hardly breath. Then you would hit the J for your last 500psi and the reg would perform as it did at 2000 psi.

At least this was my understanding...

 

[mictrik]

Last edited by mictrik; August 16th, 2010 at 10:35 PM.

 

[Zung]

Here are the numbers from the 1988 catalog:

• MK5: 87 SCFM @ 2000 PSIG, 48 SCFM @ 300 PSIG
• MK10: 80 SCFM @ 2000 PSIG, 73 SCFM @ 300 PSIG

 

[halocline]

I suspect the difference between the MK5 and 10 is due to flow characteristics in the IP chamber. The volume of the MK10 chamber is probably a little lower, but the piston head has a more conical shape. This might (a guess) result in a more pronounced 'venturi' sort-of effect in the MK10 IP air path. That could help the MK10 at lower supply pressures. MK10s also show a steeper IP drop during purge when measured with a standard IP gauge on a LP inflator hose. I never understood how this could be, but if there is more of a venturi-like effect in the IP chamber, there would be a larger pressure drop in the LP inflator hose while air is flowing through a different LP port.

Some of the MK20/25's (and MK10+) increased flow probably comes from the rounded piston edge, which I imagine has better aerodynamic properties than the knife edge. It's too bad the MK10+ lacks the nice rock-solid lock up that the MK25 has with the latest piston design. If SP had a piston that worked like that for the MK10, I'd convert mine right away.

 

[Zung]

Has anybody seen some real numbers for the flow rate of the MK10+, instead of "increased"?

The stainless steel pistons for the MK10+ are not bad: with current MK25 seats, my MK10+'s have 1 second swing to nominal IP, then 2-3 PSI of creep over a minute.

The problem is you lock yourself into buying original SP kits, or at least the SP seat if you can find it, vs the Trident seats for the straight MK10.

 

[mictrik]

One of my MK10's was upgraded to a plus back in the 90's, it has the stainless piston in it so I imagine that a later tech may of swapped it out after having trouble with lockup. I have serviced it now for a while and I never have an issue with lockup. Though I have seen the problem on other MK-10 pluses in the past I agree that the newer piston & newer MK25 seats have all but eliminated the soft lockup issue with the MK10+. I still do not think it is really worth upgrading at this point. MK10 seats are easy to find and come 3 to a kit. The MK10 is a very reliable high performance 1st stage as it is so If the increased flow rates are so important to someone they should just go with a newer MK-25.