SP reg freeflowing after pushing purge button

[nimapeace]

I've got a new SP C370 and R105 (with Mk11 1st stage) from someone on here. I just took it out to the pool for a test dive and noticed a weird thing happening. Basically, in some situations, hitting the purge button will cause the reg to violently freeflow, even after releasing the purge button. It'll only be stopped by covering the mouthpiece or switching to pre-dive. This happens on both second stages.

The two scenarios this happen are
- above water, predive knob set to dive
- underwater (about 1 ft), predive knob set to dive

I asked my LDS and they said its how the predive-adjust reg is designed to work, and that I should just keep the reg in pre-dive mode unless I'm deep (>40ft) and notice difficulty breathing.

Just wondering if that's true and also if there's any way to adjust the flow of the reg when its in dive mode to prevent this from happening. It seems unusual to dive with a reg set to "pre-dive" mode.

TIA

 

[lexvil]

That’s how they work, stop playing with the purge button.

 

[runsongas]

thats just how the venturi works. only use the dive setting when its in your mouth and purge only when you need to.

 

[fred32176]

I have a similar set up C370, R095 and MK11. Your regulator is behaving normally. A C370 provides the opportunity to have almost effortless breathing underwater, just get used to what you need to do to avoid free flows.

When I dive I have the value almost turned all the way out. That makes the C370 breathe almost effortlessly. I really like that while diving. The down side of having an almost effortless breathing is, when the regulator is not in my mouth, I need to make sure the Venturi switch is not on dive. If the Venturi switch is on dive and the regulator is out of my mouth, it can free flow in some conditions. You have a wonderful sensitive regulator that you need to get used to. Get used to only turning the Venturi switch to dive just before you put it in your mouth. It doesn't take too many dives to get used to using the C370 effectively.

.

 

[rjack321]

That’s how they work, stop playing with the purge button.

What @lexvil said ^^^
Stop diddling with the purge button.

 

[Mobulai]

It seems unusual to dive with a reg set to "pre-dive" mode

Actually it’s not an on/off switch; it’s a continuous dial.

This fully blew my mind when I first heard it last year from @rsingler : dial it back from full just a tad for best venturi effect / breathing effort / case dynamics.

Also, you purge, you start the “breathing cycle… that’s actually a good thing, it means you have a reg with a low cracking effort— it should serve you well with high gas density/depth

 

[Pearlman]

Actually it’s not an on/off switch; it’s a continuous dial.

This fully blew my mind when I first heard it last year from @rsingler : dial it back from full just a tad for best venturi effect / breathing effort / case dynamics.

I had a chance to take apart the c370 and put it back together recently. There is no moveable vane for streamlining the Venturi airflow like a wing. Instead, It is a set of rectangular holes covered by the barrel - they slide into a fully open position facing the inner roof of the mouthpiece in dive mode and slide back into a 3/4th closed position in pre-dive mode with the 1/4 open holes facing midway towards the inner celing of the body. Incidentally the diaphragm is small and is the same part borrowed from the AIR2.

It’s a beautiful performant reg and I prefer it over my S600 because of its exhaust-tee valve design borrowed from the 620Ti.

 

[keyshunter]

The purge is operating exactly as it should.

 

[rsingler]

At the surface, your second stage valve is passing a 9:1 expansion of gas (from 135 psi to 14.7 psi) that generates its own velocity wholly apart from your breath. Venturi forces are large and the C370 is especially vigorous in this regard. In fact, the Venturi gates mentioned by @Pearlman above were iteratively sized by Scubapro during the C-series development process.
IMO, they left them a hair on the excessive side for the average recreational dive, but that's an easy fix: just back off the lever 1/16". I virtually never use the Venturi lever in Pre-Dive mode, with the exception of my octo during giant stride. After that, it's back to the optimum position, which for most regs is fully open.
But like @Pearlman , I love the C370 for its easy breathing, good flow and vigorous Venturi assist. For 100ft dives, my C370 lever is wide open to help assist with thick gas flow and the reg excels.

 

[nimapeace]

Amazing, thank you all for the helpful explanations. I will stop fiddling with the purge button and enjoy the easy breathing!