7' Hose harder to breathe from?

[cool_hardware52]

Just getting into tech diving and switched to a long hose. My primary 2nd is a ScubaPro A700BT and my secondary is an A700. (Mk25bt 1st)

They've always breathed pretty much identically, but after installing the long hose, my primary is noticeably harder to breathe. Not uncomfortably so, but not the effortless breathing I'm used to. No change in my other 2nd.


Is that normal? Or could I have bad hose?

The "long hose" should actually improve the performance. The internal volume of the hose acts as a "receiver" or storage tank for gas that has already passed through the reg. Something is wrong. Probably not the hose.

Tobin

 

[Hickdive]

The culprit is probably at the regulator end of the hose. The ID of the orifice in the hose connector is probably smaller than the ID of the original hose part.

 

[cool_hardware52]

The culprit is probably at the regulator end of the hose. The ID of the orifice in the hose connector is probably smaller than the ID of the original hose part.

Unlikely. Remember breathing regs are *not* constant flow devices. They are intermittent, the diver inhales, pauses, exhales, inhales. The reg flows, stops, flows, stops.

A long hose offers a greater internal volume than a ~40 inch hose. That volume will reduce the effects of any restriction, particularly any restriction at the first stage end of the hose. A restriction at the 2nd stage *might* have some impact.

Breathe down a long hose equipped reg, i.e. charge the reg, turn off the bottle and see how many breaths are left. Most of that gas is in the hose, having already passed through the first stage.

If I was the OP, and had the original "short hose" I'd swap it back on and see it it made a difference. I suspect it won't.

Tobin

 

[DustyC]

I'm going to mess with them tomorrow, I've been working all week.

 

[Hickdive]

Unlikely. Remember breathing regs are *not* constant flow devices. They are intermittent, the diver inhales, pauses, exhales, inhales. The reg flows, stops, flows, stops.

A long hose offers a greater internal volume than a ~40 inch hose. That volume will reduce the effects of any restriction, particularly any restriction at the first stage end of the hose. A restriction at the 2nd stage *might* have some impact.

Breathe down a long hose equipped reg, i.e. charge the reg, turn off the bottle and see how many breaths are left. Most of that gas is in the hose, having already passed through the first stage.

If I was the OP, and had the original "short hose" I'd swap it back on and see it it made a difference. I suspect it won't.

Tobin

No. It was solely the orifice in the hose end at the second stage I was referring to.

Picking up two at random here, one a branded version the other generic, and putting the digital calliper over them I can see that the branded version has a 2nd stage end orifice internal diameter of 5mm whilst the other is 4.5mm. I'm sure I could find further variety if I checked some more.

That being the case the internal volume or internal diameter of the hose itself is irrelevant to how much gas can flow through that final orifice before entering the second stage.

This is why Apeks dropped the 1/2" first stage port from all the models that originally had them; they realised that the hose orifice at the second stage end was the same regardless and that, unless they redesigned their second stages so that they could only use a specialised hose with a larger inlet, the 1/2" outlet on the first stage was pointless.

 

[DustyC]

Fixed, it somehow came out of adjustment when I changed hoses. It's good to go now.

 

[halocline]

Yeah, weird stuff can happen. In some cases the longer hose serves as a reservoir or volume tank... until the hose loss and turbulent flow cancels everything out.

No, the hose always acts as an IP reservoir, not in some cases. As long as the hose is not damaged, a 7ft hose will absolutely improve the 1st stage regulator performance by reducing the IP drop during inhalation. It's just a larger volume of IP air to draw from. I don't think there's any appreciable line friction until you reach depths far far beyond air use.

Keep in mind that since IP is a constant above ambient, air through the hose is moving at the same rate regardless of depth. It's moving a lot faster through the HP valve in the first stage as it rushes to fill the IP chamber with higher pressure at depth. With a higher volume IP chamber, a smaller portion of that volume is lost with each breath, making the 1st stage's job of re-pressurizing the IP chamber that much easier.

 

[cool_hardware52]

No, the hose always acts as an IP reservoir, not in some cases. As long as the hose is not damaged, a 7ft hose will absolutely improve the 1st stage regulator performance by reducing the IP drop during inhalation. It's just a larger volume of IP air to draw from. I don't think there's any appreciable line friction until you reach depths far far beyond air use.

Keep in mind that since IP is a constant above ambient, air through the hose is moving at the same rate regardless of depth. It's moving a lot faster through the HP valve in the first stage as it rushes to fill the IP chamber with higher pressure at depth. With a higher volume IP chamber, a smaller portion of that volume is lost with each breath, making the 1st stage's job of re-pressurizing the IP chamber that much easier.

I'll add that concepts like turbulent flow, Reynolds numbers etc. really only matter in constant flow systems. We all breathe at less than a 100% duty cycle…..

Tobin

---------- Post added November 16th, 2015 at 06:35 PM ----------

No. It was solely the orifice in the hose end at the second stage I was referring to.

Then say so. You said "reg" there are two regs a first stage and a second stage

Picking up two at random here, one a branded version the other generic, and putting the digital calliper over them I can see that the branded version has a 2nd stage end orifice internal diameter of 5mm whilst the other is 4.5mm. I'm sure I could find further variety if I checked some more.

What's the orifice size in the 2nd stage? I'll bet money is many times less cross section that 4.5 mm (.18") With a delta P of ~150 psi a .180" orifice would flow ~50 scfm which is just a *bit* more than the typical sac rate for most divers…….

That being the case the internal volume or internal diameter of the hose itself is irrelevant to how much gas can flow through that final orifice before entering the second stage.

Only in a constant flow application. Humans don't inhale constantly.

BTW, the OP determined his *reg* was out of adjustment and his problem had zero to do with the hose.

Tobin