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Old 26 September 2006, 18:27   #1
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Tube Pressure.

Might seem like a stupid question but how do you tell, if you haven't got an indicator, if your tubes are the correct pressure ?

I prefer really firm tubes (oooer) but often wonder if these pass too many stresses to the rest of the boat.

As temperatures are now beginning to cool I've noticed the tubes are a bit flaccid.

Would I be correct in pumping them up hard or leaving a bit of give in them.

?
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Old 26 September 2006, 18:34   #2
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normal tube pressure is aprox 6 PSI.
when it gets cold the air in the tubes contract so the tubes get soft so go ahead and re pump the tubes with the foot / electric pump...... not like a local dive club who used their dive bottle and burst the tubes.
Most modern ribs have safety overpressure valves that will open if the tubes are over pressurised.
Saw a rib tube gauge on ebay last week for small money. When I locate it again I will post the link here

Sparkey.
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Old 26 September 2006, 18:40   #3
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Wouldnt' having slack tubes pass more stresses on to certain areas and less onto others? I can visualise more stress on extremities for example-and more stress on the hull/tube joins as there would be more of a tearing effect by the tubes as you landed/hit waves etc-something like having a flat tyre?

Correct me if I'm wrong here-it's just a theory.
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Old 26 September 2006, 18:48   #4
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Nos,

Dunno the answer to your reply. But if you haven't got a gauge how do you know if you've got 6 PSI Sparkey. Is that hard or very hard or not quite so hard.
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Old 26 September 2006, 18:52   #5
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Quote:
Originally Posted by Nos4r2
Wouldnt' having slack tubes pass more stresses on to certain areas and less onto others? I can visualise more stress on extremities for example-and more stress on the hull/tube joins as there would be more of a tearing effect by the tubes as you landed/hit waves etc-something like having a flat tyre?

Correct me if I'm wrong here-it's just a theory.
Yes Nos2r4 , I follow your thinking.
if the tubes are correctly inflated then any impacts or stress will be distributed across a bigger surface area.
Also the rib will be easier to handle and safer as well as dryer to use as the hard tubes will deflect any spray out and down

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Old 26 September 2006, 18:53   #6
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Quote:
Originally Posted by sparkey
normal tube pressure is aprox 6 PSI.

it's not that high is it? I've never had a gauge but heard 2-4psi bandied about as normal. Always just pumped mine up hard enough that you just get that satisfying 'boing' sound when you slap them with a palm.
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Old 26 September 2006, 19:00   #7
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But would tubes that wobble about when making progress be too soft. They aren't overly soft but nonetheless they ain't rock hard. Can we assume that rock hard to the touch are the best condition to have your tubes.
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Old 26 September 2006, 19:04   #8
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Quote:
Originally Posted by Biggles
But would tubes that wobble about when making progress be too soft. They aren't overly soft but nonetheless they ain't rock hard. Can we assume that rock hard to the touch are the best condition to have your tubes.

I'd guess that wobbling is bad-though I'd have to inflate mine to more than my pump would allow to stop them moving completely.

I think we need Paul Tilley here.
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Old 26 September 2006, 19:30   #9
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I'm sure the experts reply would be of value to all of us.
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Old 26 September 2006, 19:57   #10
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Quote:
Originally Posted by sparkey
normal tube pressure is aprox 6 PSI.
when it gets cold the air in the tubes contract so the tubes get soft so go ahead and re pump the tubes with the foot / electric pump...... not like a local dive club who used their dive bottle and burst the tubes.
Most modern ribs have safety overpressure valves that will open if the tubes are over pressurised.
Saw a rib tube gauge on ebay last week for small money. When I locate it again I will post the link here

Sparkey.

We haved dived for years with a leaky old Osprey 5.5 that goes down so fast, dive bottles are the only way to get the lost Volume in (just don't go daft) we have even made a connection for system-sorting the leak would obviously be better but it's turned into a bit of a game.
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Old 26 September 2006, 20:58   #11
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6.5 psi seems a little high to me. We usually run about 3.5 -4 psi. you can get a gauge with an adapter that you put in the tube filler valve for about $5 that gives you an accurate reading.
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Old 26 September 2006, 22:32   #12
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IIRC the label on the console of my Humber says 0.2 bar which is 3psi....

When I first got my boat and was leaving it moored to a pontoon I used to just run it "as it was on the day" which since I left it soft to be on the safe side when the sun came out (big black boarding wear patches which heat up!) meant it was rather wobbly.

Since having it out of the water over the winter and pumping it up each time before I launch, I have to say the boat feels much much better with correctly inflated tubes than when running them a bit soft. Having thought about it a bit I came to the same conclusion as Nos4r2 - that having them too soft puts a lot of stress on certain areas with the tubes flapping around and wrenching at certain points, especially where they go on to the transom which seemed to take a real hammering.. I just wish I had PRV's so I could leave them hard all the time

An ATV quad bike tyre runs about 3psi and it will deform with a firm poke of the finger but only by a couple of inches so the "poke test" is the yardstick I have used when inflating mine recently - hope it is not too far out!

When I deflated mine to do some repairs I reinflated them with the mains compressor in my garage (100psi) but only till they were almost back into their normal shape then finished off with the tube pump to be on the safe side. Didn't half save some time though!

I looked at a tube pressure gauge from Polymarine here but it was over £30 which seemed a lot to me!
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Old 26 September 2006, 22:34   #13
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Quote:
Originally Posted by Biggles
But would tubes that wobble about when making progress be too soft. They aren't overly soft but nonetheless they ain't rock hard. Can we assume that rock hard to the touch are the best condition to have your tubes.
On a RIB with the tubes clear of the water not really - look at a balloon - when is it easier to burst - when it's blown up tight as a drum or when it's a bit wrinkly???
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Old 26 September 2006, 23:13   #14
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Quote:
Originally Posted by codprawn
On a RIB with the tubes clear of the water not really - look at a balloon - when is it easier to burst - when it's blown up tight as a drum or when it's a bit wrinkly???
I suspect Biggles's tubes are at the happy medium between the two-same as mine. Hard enough to keep shape and not wobble all over the place but soft enough to deform in a bad stuff so they don't pop.
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Old 27 September 2006, 05:47   #15
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Quote:
Originally Posted by Nos4r2
I suspect Biggles's tubes are at the happy medium between the two-same as mine. Hard enough to keep shape and not wobble all over the place but soft enough to deform in a bad stuff so they don't pop.
Interestingly when I was looking at pressure relief valves recently (still no answer about my design for a screw on one - lazy gits!) one of the benefits given was to prevent overpressure in extreme rough conditions or collisions.

I think this is probably marketing tosh though - if you wallop something hard enough to pop a Hypalon tube, you surely ain't going to get a significant volume of air out through a half-inch hole in the timescale needed (probably about 1 second) to make any difference?!
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Old 27 September 2006, 05:52   #16
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I agree, although fitting multiple PRV's is sometimes the answer. PRV''s are usully fitted to prevent over pressure in hot climates/conditions.
Standard pressure for a tube should be 3.0 PSI, the PRV's that we fit open at 4 PSI.
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Old 27 September 2006, 07:42   #17
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Quote:
Originally Posted by BogMonster
Interestingly when I was looking at pressure relief valves recently (still no answer about my design for a screw on one - lazy gits!) one of the benefits given was to prevent overpressure in extreme rough conditions or collisions.

I think this is probably marketing tosh though - if you wallop something hard enough to pop a Hypalon tube, you surely ain't going to get a significant volume of air out through a half-inch hole in the timescale needed (probably about 1 second) to make any difference?!
Exactly - they are there for gradual pressure release due top weather conditions etc. It would be a bit like expecting a tyre valve to pop off to save your tyre when you hit a pothole!!!
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Old 27 September 2006, 15:08   #18
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Quote:
Originally Posted by BogMonster
Interestingly when I was looking at pressure relief valves recently (still no answer about my design for a screw on one - lazy gits!) one of the benefits given was to prevent overpressure in extreme rough conditions or collisions.

I think this is probably marketing tosh though - if you wallop something hard enough to pop a Hypalon tube, you surely ain't going to get a significant volume of air out through a half-inch hole in the timescale needed (probably about 1 second) to make any difference?!
Stephen,

What they possibly mean is that the tubes wouldn't already be overpressure before any incident, not that they would release air on impact. ie the tubes would already be at an optimum pressure, not rock hard ready to pop!
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