What flows faster?

[CenTexDivin]

I was just curious about something. I had talked with someone at the lake a few weeks ago, and during the conversation, the topic of sheared off hoses came up. He brought up a point that he believed that if the HP hose with your gauges was sheared off at the end, that it would take around 20 min for it to empty a full AL80, whereas if your LP was cut off, it would empty in only a few minutes. After asking, he explained that the small pinhole opening that the HP air goes through would block the flow more than the less restrictive LP hose.

After asking my instructor, he said the high pressure would cause the air to leak faster, and additionally, if your LP hose had a leak, you could put a kink in it to prevent the air from flowing at such a fast rate, like a garden hose.

I understand both arguments, one being that the amount of space through which the air can flow determines how fast the air can flow out, whereas the other argument is that the high pressure will force the air out faster.

So.... who's right?

*disclaimer- this is hypothetical, theoretical, and not to be attempted, just a point of information.

 

[mike_s]

just wait... someone with an old regulator will try this tonight and test it just because they've just 'got to post it'.

 

[Cave Diver]

We tested this theory several years ago and the conclusion we came to was the low pressure hose emptied the tank considerable faster. It was also easier to kink the low pressure hose to restrict flow.

 

[spectrum]

Assuming that the HP does have a pinhole port (anything modern will I believe) upstream of the failure it will loose air very slowly.

A LP full failure will be drain a full cylinder in a few minutes.

Note that if the LP failure was the result of a runaway intermediate pressure in the first stage that folded hose may rupture too. In some cases folding that LP to closure is more easily said than done, it's not a garden hose.

I side with your buddy at the lake.

Pete

 

[Cave Diver]

just wait... someone with an old regulator will try this tonight and test it just because they've just 'got to post it'.

An old reg isnt necessary. You dont have to cut or rupture the hose, just unscrew the second stage or gauge from the end of it, same result.

Of course, whenever we tried it a few years ago we did slice n dice some old hoses, just for realisms sake...

 

[fweber]

I concure. As long as the HP fitting with flow restrictor is left in the first stage, a burst or cut hp hose will result in a slower leak than an unrestricted lp hose failure. Somewhere along the lines, Curt Bowen did a great write up on this very subject for Advanced Diver Mag. If I remember correctly, he went so far as to unscrew burst disks in an effort to time all the possible failure modes.

 

[Scottri]

LP will drain a tank much faster than the HP port.

 

[Charlie99]

As long as the HP fitting with flow restrictor is left in the first stage, a burst or cut hp hose will result in a slower leak than an unrestricted lp hose failure.

New regs, such as my 9 year old Atomics B1, have the flow restrictor built into the regulator internal passages. No need for a restrictor in the hose fitting or coupling.

If you have doubts about whether your reg has an internal flow restrictor, simply remove the HP hose. It will look like there is just a blank plate feeding the hose. The pinhole is very small.

 

[MissyP]

According to my TDI book (for Adv Trimix) using an 80cuft tank, here are the times it takes to drain w/ different failures at different depths:

0 ATA-- burst disk failure = 72 seconds
4 ATA-- burst disk failure = 72 seconds
8 ATA-- burst disk failure = 72 seconds

0 ATA--Ruptured LP Hose = 83 seconds
4 ATA--Ruptured LP Hose = 83 seconds
8 ATA--Ruptured LP Hose = 83 seconds

0 ATA--Ruptured HP Hose= 22 min
4 ATA--Ruptured HP Hose= 22 min
8 ATA--Ruptured HP Hose= no data

0 ATA-- Freeflowing Regulator= 255 seconds
4 ATA-- Freeflowing Regulator= 155 seconds
8 ATA-- Freeflowing Regulator= 91 seconds

*LP hoses drain more quickly because they deliver a larger amount of air through the hose (reg) whereas, HP drains slower because the opening isnt much bigger than a needle because less air flow is needed (such as for a pressure gauge).

 

[CenTexDivin]

*LP hoses drain more quickly because they deliver a larger amount of air through the hose (reg) whereas, HP drains slower because the opening isnt much bigger than a needle because less air flow is needed (such as for a pressure gauge).

Just what I was looking for. Thanks.


BTW, I hate that there's a San Marcos, CA. It makes looking for local businesses in San Marcos, TX a pain.