bov hose
- Thread starter markdol1
- Start date
Michael Thornton
Rebreather Enthusiast
High Pressure hoses typically have a smaller diameter that might not give the volume of gas needed for breathing from. I would not recommend doing anything to decrease the WOB of your BOV.
markdol1
CCRX Supporter
Hi mike ,thats the question if the fitting has enough material to drill out to give the same flow as a 3/8 orofice. I would think the hose id at 140 psi will be enough for bov demand.
Last edited:
Michael Thornton
Rebreather Enthusiast
It's not just the fitting diameter it is the internal diameter of the hose. HP hoses are typically really small internal diameter. Low Pressure quick disconnect hoses are larger and low pressure regulator hoses are even bigger than quick disconnect hoses. This is why safe seconds such as the Atomic SS1 or Aqualung Airsource or equivalents use a low pressure regulator hoses with a large quick disconnect adapter rather than using a quick disconnect hose. For breathing off of you need the high flow larger diameter (internal diameter) of a regulator hose.
I'm afraid this is a bit of an urban legend. Our company has sold literally thousands of braided hoses over the past few years and although we have experienced the typical hose failures (leaks around crimping) we have not seen a single hose failure like what you have described. I honestly believe that the "inner plastic breakdown legend" is something that was started by one of our competitors who does not have the capability to manufacture braided hoses.
It's definitely not an urban legend, there are at least 2 DAN reported incidents so far.
http://www.danap.org/DAN_diving_safety/polymorphic_crystallisation.php
http://www.danap.org/DAN_diving_safety/polymorphic_crystallisation.php
CCR Josh
"Rebreather Enthusiast"
Just wanted to point out a few sections from the DAN article you posted:
"However, it would be foolish to assume that this deterioration is limited to external 'braided' hoses. In the past, our hoses comprised a rubber inner hose, then a single braid layer for reinforcement, and finally a rubber, outer 'sealing' layer. In the modern era, the rubber inner hose is sometimes replaced with typically polyurethane or nylon hose (referred to as thermoplastic). The middle or reinforcing layer is a polymer filament braid, and the outer layer either a second braid – which as the advantage of telling you when inner hose has a leak, or a polyurethane or a synthetic rubber outer sealing layer.
The reality is that the newer, second stage hose with a thermoplastic inner layer may be vulnerable to degradation. In our industry, 'newer' means possibly even up to 15 years or longer. This does not, however, apply to synthetic rubber internal layers, which appear to be impervious to this phenomenon."
"the internal section of all newer hoses which use a thermoplastic inner layer appears to be uniquely prone to 'polymorphic crystallisation’"
"A physical examination including squeezing the hose every couple of inches to assess whether the hoses exhibits the same degree of flex should indicate if all is well. Any indication of a change in the resistance while squeezing along the length of the hose would be good sign that all is not well.
This test, on the braided hose, is in fact much easier to perform than with the harder, outer 'rubberized' hoses."
I would also like to point out that various hoses (rubber or "braided") from different manufactures have several choices of material for this "thermoplastic inner tube". Just like most things in life, there are various levels of quality (and usually cost) to choose from. For example, in general, TPU might be a better choice than PVC. I know that there are hoses on the market that use both materials (SubGravity uses TPU). PVC will tend to discolor and harden over time, where TPU does not.The reality is that the newer, second stage hose with a thermoplastic inner layer may be vulnerable to degradation. In our industry, 'newer' means possibly even up to 15 years or longer. This does not, however, apply to synthetic rubber internal layers, which appear to be impervious to this phenomenon."
"the internal section of all newer hoses which use a thermoplastic inner layer appears to be uniquely prone to 'polymorphic crystallisation’"
"A physical examination including squeezing the hose every couple of inches to assess whether the hoses exhibits the same degree of flex should indicate if all is well. Any indication of a change in the resistance while squeezing along the length of the hose would be good sign that all is not well.
This test, on the braided hose, is in fact much easier to perform than with the harder, outer 'rubberized' hoses."
Overall, I would agree with the DAN article that hoses should be checked and replaced often enough to avoid most problems with them. I also agree that it is foolish to assume that this problem is specific to "braided" hoses. To me, the simple answer is to replace your hoses every few years or more often if your inspections (or conscience) dictates.
Hope this helps anyone who reads it!
CCR Josh
"Rebreather Enthusiast"
Mark
Thought I would jump in here since I am on a posting frenzy at the moment
I am no math wiz, but a quick google search shows some formulas which might over our heads, but essentially come out to: If the diameter of the tube is halved the flow through it reduces to one sixteenth. Length also affects flow, and that BOV hose is not the longest in the world, but it's not the shortest either: If the length is doubled the flow is halved.
You combine the above with the fact that a BOV will never be as high as performance as the top second stages in the world (due to the fact that the actual regulator has to been further away from your mouth on a BOV) and I would submit that we want the absolute highest flow we can get, within reason of course.
Ok.... time to let someone outside the family respond
I've seen it with my own eyes, and there's plenty of accounts of this happening posted to various forums.
Never once seen or heard of this happening with a rubber hose.
Not saying that it is not possible, but as the DAN article states, users regularly inspecting their hoses for damage, whether rubber or braided is prudent. According to DAN, " it would be foolish to assume that this deterioration is limited to external 'braided' hoses."
All hoses need to be checked for wear and tare, and the other thing to keep in mind is that there are several different materials used (depending on the manufacturer) for interior tubing on dive hoses, so hose durability can vary quite widely from manufacturer to manufacturer.
markdol1
CCRX Supporter
Thanks for the imput from all.I was concerned about hose flow of a smaller diameter at pressure still being adequate along with opening the fitting orofice. Short of cutting the hose in half an putting it on a flow bench at the normal ip i thought i would ask. I wont stick my head up the bulls butt to see if the steak is good ill just take the word of the butcher! As far as 2 reports to dan of internal breakdown of theese hoses discussed i would not call it as being PRONE .I have and still use different make braided hoses hp and lp since they came out without 1 case of failure or degradation , Not that it cant happen i am just going on what i am seeing with the regard to numbers sold and used wordwide. I will usually lean towards the side of empirical data on most things in life.
Last edited:
Tim1
Member
Does this imply that SubGravity does have the capability to manufacture braided hoses?
Josh, Absolutely nothing physical preventing a BOV having the same performance as the top second stages. See http://www.deeplife.co.uk/or_files/DV_DL_ALVBOV_Breathing_Params_A3_100318.pdf and also the Poseidon BOV. Just takes R&D to get it right....
For the OP, I understand that ~1/4" is the minimum bore you want in the flow path from 1st stage to BOV, for a BOV that meets or exceeds EN250 requirements. This includes any fittings or QC's.
But perhaps also consider if the BOV doesn't meet EN250 up front as a bare minimum, you have no clue how well it performs in the first place. So supplying it via spaghetti thin hose might in reality not actually make much difference.