Tubes pressures - Page 2

Scary Des · 23 November 2005, 10:35

Quote:

Originally Posted by jwalker

Anyone know what pressure blow-off valves blow off at?

Seems like any pressure from 1psi to 10 psi Look at this

Been thinking about these myself and I can’t decide if I need one in every chamber

My thinking is that if I start inflating at the front of the boat the inter-chamber cones point rearwards so by the time it get to the rear chamber on one side it is a cone smaller than its total size so any expansion can take place into the chamber before it. Does this make sense or am I missing the point

Des

Tim M · 23 November 2005, 10:37

I used to have a quicksilver SIB. You had to seriosuly inflate that if you followed the instructions. From memory the tubes were about 2.5 and the floor was even more, possibly 4. Codders can correct me as he has this boat.

Jackwabbit · 23 November 2005, 10:40

Quote:

Originally Posted by roycruse

Are you sure it wasnt just the floor that was supposed to be at 2.5 PSI and not all the tubes.

I used to have a Metzeler SIB that had a honey comb deck and it had to be at a much higher pressure than the tubes.

No! their quote to me was "pump the keal as hard as you can get it & the rest of the tubs to 2.5psi"

Nate · 23 November 2005, 10:45

I was thinking about fitting these to my tubes and approached Henshaw Inflatables. Supplying them was no problem as they're a stock item, but when I spoke to Kevin, the factory manager, he reckoned that they're not worth fitting in our climate, and could even be less than useful inasmuch as they'd release pressure on a hot day, but if left unattended, the boat would end up being underpressured when the temperature dropped. He also said that although the P22 should be pumped to 2psi, the tubes are designed to be happy when things heat up and the pressure rises to as much as 3.5psi.

Perhaps someone with an Avon should speak to the factory for their advice?

jwalker · 23 November 2005, 11:31

Quote:

Originally Posted by Scary Des

Seems like any pressure from 1psi to 10 psi Look at this

Been thinking about these myself and I can’t decide if I need one in every chamber

My thinking is that if I start inflating at the front of the boat the inter-chamber cones point rearwards so by the time it get to the rear chamber on one side it is a cone smaller than its total size so any expansion can take place into the chamber before it. Does this make sense or am I missing the point

Des

Ta. It looks as though I need to find out the spring colour. Your second link here

also had a PDF which gave the list of spring colours against pressures from 0.5 - 13.4psi.

With the tube baffles I work from the rear inflating both sides. The cones will be pushed forward, the next will also be pushed forward as will the next. Finally, I inflate the front section to be harder than I'd made the others. This will pressurise all the other sections to the same pressure by forcing the cones back toward their respective sections. It also allows a bit of deflation of any section whilst keeping all the pressures the same because the cones can move to compensate.

Jono · 23 November 2005, 11:42

Quote:

Originally Posted by jwalker

..
With the tube baffles I work from the rear inflating both sides. The cones will be pushed forward, the next will also be pushed forward as will the next. Finally, I inflate the front section to be harder than I'd made the others. This will pressurise all the other sections to the same pressure by forcing the cones back toward their respective sections. It also allows a bit of deflation of any section whilst keeping all the pressures the same because the cones can move to compensate.

There ya go again, JW... thinking things through properly... you'll wear your brain out at this rate.... I intend making my brain last as long as possible, by treating it gently....

Scary Des · 23 November 2005, 11:45

Quote:

Originally Posted by jwalker

......With the tube baffles I work from the rear inflating both sides. The cones will be pushed forward, the next will also be pushed forward as will the next. Finally, I inflate the front section to be harder than I'd made the others. This will pressurise all the other sections to the same pressure by forcing the cones back toward their respective sections. ........

So with one pressure relieve valve in each of you rear chambers you could de-pressurise all your chambers by the volume of the inter-chamber cones

Or am missing something

roycruse · 23 November 2005, 11:51

Quote:

Originally Posted by Scary Des

So with one pressure relieve valve in each of you rear chambers you could de-pressurise all your chambers by the volume of the inter-chamber cones

Or am missing something

There not actually cones though are they ? They are flat baffles - which means the additional volume available will only be the amount that that baffle can deform - which i would imagine would only allow or a few litres - or in other words a very small percentage of the total volume of a chamber.

I dont know for sure - but my guess would be that this would not supply sufficient protection.

jwalker · 23 November 2005, 12:01

Quote:

Originally Posted by roycruse

There not actually cones though are they ? They are flat baffles.

I wouldn't bo too adamant about that, if I were you.

roycruse · 23 November 2005, 12:06

Quote:

Originally Posted by jwalker

I wouldn't bo too adamant about that, if I were you.

I wasnt - note the question mark - I was actually asking a question !!!

jwalker · 23 November 2005, 12:09

Oh, sorry. I thought you said they are flat baffles and therefore could only displace a few litres. My mistake.

Jackwabbit · 23 November 2005, 12:19

Quote:

Originally Posted by roycruse

There not actually cones though are they ? They are flat baffles - which means the additional volume available will only be the amount that that baffle can deform - which i would imagine would only allow or a few litres - or in other words a very small percentage of the total volume of a chamber.

I dont know for sure - but my guess would be that this would not supply sufficient protection.

The ones in our Avon were defiantly cones; well after it went bang they were more like funnels.

roycruse · 23 November 2005, 12:30

Quote:

Originally Posted by jwalker

Oh, sorry. I thought you said they are flat baffles and therefore could only displace a few litres. My mistake.

Ahh - i did say that - One of the disadvantages of talking in text - intonation is lost...

Ill try to clarify what i meant to say.

I am of the opinion that in my boat the baffles are flat - for no other reason than how they behave when i lower the pressure in one chamber. But I could be wrong - hence i said "are they" and put a question mark on the end.

I then went on to say - that being flat I thought they would not offer sufficient cross chamber protection for the purposes of pressure relief.

If however they are cones - i would still question their ability to sufficiently depressurise the adjacent chamber in an over pressure situation.

I was not trying to pick a fight - just trying to learn something by throwing in some comments.

jwalker · 23 November 2005, 12:34

Quote:

Originally Posted by roycruse

Ahh - i did say that ...

Andy Gee · 23 November 2005, 13:36

Quote:

Originally Posted by Nate

he reckoned that they're not worth fitting in our climate, and could even be less than useful inasmuch as they'd release pressure on a hot day, but if left unattended, the boat would end up being underpressured when the temperature dropped.

He wants to selltubes though

. They do work and once this year mine let out some air.....it was the day we had 29d. I doubt that they would let enough out to make the boat underpressured, as you would have topped them up by that time

codprawn · 23 November 2005, 13:50

Quote:

Originally Posted by Tim M

I used to have a quicksilver SIB. You had to seriosuly inflate that if you followed the instructions. From memory the tubes were about 2.5 and the floor was even more, possibly 4. Codders can correct me as he has this boat.

Yes quite right.

As to pumping up the tubes in sequence I am very carefull not to put too much air into any one chamber before getting them all pretty much even - then just top them up to final pressure.

I like the comment about sticking a pin in a balloon - obviously the higher the pressure the more likely it is to burst suddenly.

Someone made a valid point about the tubes flapping around etc if not inflated enough which could cause damage. I would say the opposite is true. If the tubes are so hard they don't deform a little then surely MORE stress will be applied to the bonded fixing???

Tim M · 23 November 2005, 23:54

THe quicksilver is heat welded together and I dont think is very prone to coming apart; I burst the bow on mine and the back stayed infalted. I think the baffles in the bow face the stern so in theory if the seams had been weak the hole boat would have blown.

Hugh Jardon · 24 November 2005, 00:49

on fitting pressure release valves i think it may depend on the tube colour to an extent, ie black tubes will draw more heat than white tubes so fitting the valves on darker tubes is what the tubing guys seem to advise, also on quicksilver the main tubes are 2.5 or so (cant remember exactly as it is on the pump gauge) but the floor is nearer 10 on the airdeck model i have

wavelength · 24 November 2005, 10:18

we have pressure relief valves in all our boats-black boats and yellow ones. Wouldnt be without 'em. I can run the tubes nice and hard without worry and I can leave them without watching for the sun all the time. Many years ago a certain lifeboat station left a pumped up "D" class out in the sun while they rattled the collecting tin-and split it !