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Pressure gauge accuracy

 
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Cristian



Joined: 17 May 2011
Posts: 1

PostPosted: Tue May 17, 2011 7:54 am    Post subject: Pressure gauge accuracy Reply with quote

Hi,

Few weeks ago the main tube of my Lagoon 1 kayak developed a small tear of about " at the outside edge of tube #1, near the seam. This looked like being the effect of some overinflation but this is strange as I always used a Sevylor Pressure Gauge (owned from a previous kayak) to measure the pressure.
I suspected that the Sevylor Gauge was not correctly indicating the inflating pressure so I purchased AE's Inline Valve Adaptor with Gauge.
As expected the 2 gauges indicated different pressures: the Sevylor lower pressure / the AE Gauge higher pressure.
I thought of a method to evaluate the accuracy of the indications.
I remembered what I learned in school about pressure: I used a 6ft hose filled with water curved in a U shape - in equilibrium the water level is the same. Than I fit the pressure gauge at one end and raised the other end of the hose in order to create pressure difference.
According to the physics law the pressure p=rho*g*h where rho is water density (constant), g=gravitation acceleration (constant), h=height (variable, equal to the difference of water level in the two ends of the tube). Pressure is independent of the hose section.
By solving the equation, p=2psi is achieved when h=4.6ft.
I checked both gauges and surprisingly both showed inaccurate values!
A 2psi pressure was indicated as 1.8psi by Sevylor and as 2.5psi by AE.
The other way round, a gauge indication of 2psi was in reality 2.3psi for Sevylor and 1.6psi for AE.

After this long description comes the question: how sensitive is the tube to pressure variations? Is it better to underinflate in order to avoid tube seam failures?
Any feedback is welcome!
Cristian
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PJohanson



Joined: 01 Jun 2007
Posts: 620
Location: Vancouver Island, Canada

PostPosted: Wed Jun 08, 2011 4:53 pm    Post subject: Reply with quote

I have an older version of the Lagoon, and I'm happy underinflating it. The kayak floats and rides fine 90% full. This leaves a little room for the air to expand on a sunny day, even though the cold water keeps it pretty cool.
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evgenk



Joined: 25 Apr 2011
Posts: 38
Location: Toronto, ON, Canada

PostPosted: Thu Jun 09, 2011 8:05 am    Post subject: Reply with quote

I never thought that gauge was terribly accurate ... I would also imagine that accuracy would vary from gauge to gauge even if it's from the same manufacturer.

I've been using inflatables for a while and have never had any issues with over inflation or have never observed that the air chambers would be extremely sensitive to air pressure variations. In regular inflatables the PVC hull would also expand in the sun along with the air inside it thus somewhat compensating for the higher air pressure.

However, the above is probably not the case with Advanced Elements kayaks since the PVC air chambers are enclosed in a nylon tube which does not really expand, which means that higher air chamber pressure would put extra load on the nylon tube skin which in turn could cause it to rip at the seams.

I don't think there would be a clear answer on how sensitive this nylon skin is to air pressure variations as it would greatly depend on the quality of the seam, previous wear on the seam and the size of the main tube. Larger tubes would have much larger surface areas and the pressure would be distributed more equally thus making it more tolerable of higher pressures. It's possible there simply was a weak spot in the seam where it has ripped.

These are just my observations - AF people, please correct me if I am wrong.

I use the AE double action pump with gauge and always inflate the main tubes to around 2.5psi knowing that I'd lose some air while unscrewing the pump from the valve and due to the water cooling the air down a bit. This is on an AF Convertible btw.
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vsj



Joined: 30 May 2012
Posts: 10

PostPosted: Wed Mar 02, 2016 12:44 pm    Post subject: Reply with quote

I have used an AF1 for about 4 years. Not having owned a pressure gauge I've always inflated the main chambers to the point where they, in my opinion, feel comfortable on water and "firm to touch" like it says in the manual.

Today I got a new Expedition and the AE hand pump with a pressure gauge. Although I've always known that I'm probably somewhat overinflating, I was quite surprised by at how low pressure the gauge measures 2 PSI! Perhaps I would've been better off now knowing :D I've been paddling happy with a firm AF1 without any problems but now I hesitate to even test how high the gauge goes if I fill the new Expedition's chambers up as much as I'd like to.

Anyway... happy to read Cristian's post about the AE gauge indicating a lower-than-actual pressure. Maybe I can pump an extra .5 in there without blowing up my new rather expensive (after VAT and shipping) kayak during its first summer. :)
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JCOOLEY
Site Admin


Joined: 20 Feb 2007
Posts: 913
Location: Benicia, CA

PostPosted: Thu Mar 03, 2016 10:48 am    Post subject: Reply with quote

A little extra won't hurt anything. A lot extra will.
I cold conditions I put in a little more to compensate for the cold temperature outside or in the water because it will lose some pressure.
On Hot days, I stay closer to the recommendation because the pressure will increase with the sun beating down on it.

If I leave it resting on shore on a hot day, I make sure to let out some air.

2.5 psi will be perfectly fine.
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