Author Topic: Pressure Gauges and Wings  (Read 471 times)

Fishman

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Pressure Gauges and Wings
« on: May 21, 2020, 05:14:18 PM »
 Lately I've seen some blown out wings. I can't help but wonder if the wings were over inflated. I'd hate to have my wing blow out because i trusted a bad pressure gauge. I already suspected my pressure gauge was off' so i figured id test it to find out for sure.

 I bought some new gauges, and had a couple lying around the shop. I put together a little testing rig to see what i can see. It turned out my pump gauge was way off and even the new "better" gauges came with issues. Below is the results of testing the 4 new gauges.
( I tested some older small air filled gauges that were waaay the hell off, but i did not include them because they weren't new.)



A) My wing pump "air filled" gauges was off by a little more that 4.0 PSI. It said 11 PSI when actually it was at 7 PSI
It's a small diameter 0-30 psi Gauge. So yeah my first few times out on the wing i was under inflated.

B) I had a new 2 1/2" 0-30 PSI oil filled in the shop so i tested it  It said 5 PSI when it was at 7 psi
(*** that was the un-vented reading. There is a vent plug on oil filled gauges that is suppose to be opened before use, but the way this one is sold you have no way of knowing that so i tested it as is. Once it was vented to your Atmosphere it was very close, maybe a 1/2 PSI off at 7 PSI)

C) I bought A new oil filled 0-15 PSI it said 7 PSI when it was at 7 PSI. Yep it was spot on. Even at 1 PSI it was spot on
https://www.amazon.com/dp/B00G008GHS/ref=cfb_at_prodpg This one had a sticker on it telling you to vent the gauge before use. Before venting it would have been 2 psi below actual reading. IMO This is a really nice gauge for wings and the perfect range for accuracy.

D) Digital PSI gauge it said 4.5 PSI when it was 7 psi.
*** This one was a mystery because it was way off at first, 3.5 psi. It would not start to read any pressure until 3.5 PSI.
While i was testing i cycled it through the function button one more time and low a behold, It became spot on. ???  From 0.25 psi up to 8 PSI it was absolutely perfect !.   https://www.amazon.com/gp/product/B07CXMBXRP/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1

My testing was a rig i built that i could hook all the gauges up to it at the same time so all gauges were exposed to the same pressure (in parallel).
For accuracy i used a water column for reference 27.07"= 1 psi  18' tall so max i measured was 8 PSI. 

I ended up using both the 0-15 oil filled, and the digital gauge together teed onto my air pump. It's overkill but for me there's some peace in knowing that I know I didn't put too much air in.
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Dwight (DW)

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Re: Pressure Gauges and Wings
« Reply #1 on: May 21, 2020, 06:34:39 PM »
There are multiple problems we cannot solve. Wings have check valves. This backflow prevention makes getting an accurate reading near impossible.

Even expensive pressure gauges foul so easy. I have filter protection on my vacuum pump gauge and they still go bad after about a year. Just replaced another one on my vac pump. Kite pump gauges are worse.

Itís really just a wild ass guess with these gauges. Feel and years of kiting experience help.

A few wings have blown up here. Some brands are not using the same seam construction/sewing method on the center strut, that is used on the leading edge. That is a huge screw up. The center struts have blown on every wing Iíve seen fail. My buddy has had two center struts re-sewn that were showing a bulge, indicating Seam failure was coming soon.


PonoBill

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Re: Pressure Gauges and Wings
« Reply #2 on: May 21, 2020, 10:00:47 PM »
My current pump doesn't have a gauge--the last two did, and I can only assume they are working accurately wherever they are and whoever is using them. I'm actually more comfortable using the gauge-less one since it gets really hard to pump at about 8 psi (I tested it). Ignorance is bliss.
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

Solent Foiler

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Re: Pressure Gauges and Wings
« Reply #3 on: May 21, 2020, 10:09:55 PM »
Really interesting experiment! Thanks for putting in the effort and sharing. Take away is that they generally read under - but not surprising given the check valve as DW said. If in doubt go over!

The manufacturers really should offer some advice here - some indicators that wing pressure is ballpark right (Gong is the only one I've seen so this so far)

Presumably you removed and reattached the valves a few times each, and your reported values are the consistent readings? Interested to know about the variability of the readings per gauge and whether that's an issue too.
« Last Edit: May 21, 2020, 10:11:26 PM by Solent Foiler »
I'm 5'10", 65kg riding:
Naish Hover Crossover 120
Gong Catch 5'3"
on Naish foils (1250 & 1650).
Gong Plus wings - 4m, 5m

Fishman

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Re: Pressure Gauges and Wings
« Reply #4 on: May 22, 2020, 11:11:31 AM »
Back in the day reading pressure gauges in the pneumatic shop at Delta Airlines is what i did for a living. 15 years of that embedded in me the verify and trust your readings approach to all things air. So for me trusting myself feeling the wing, over a gauge reading is NOT something i can do, maybe in time that will change.

 I can see where a lot of things could influence your readings on a big ole kite catching the fluctuating wind, check valve... The stock gauge that comes with some pumps are just  not good IMO. Even if it is steady it hard to get a good read on it. I can say that with larger 0-15 oil filled you will get a much easier more accurate read. My reading on the wings i use with the digital gauge is very close to accurate. I'd say less than 5% off, which to me is acceptable. The few last strokes of the pump smooth and slow can bring it from a fairly steady 7.9 to a steady 8.0 psi on the digital.

Solent foiler,   it's funny you mention Bear's video. It was his air pump that was off by over 3.5psi. I can definitely see trusting the feeling over the gauge in that case. That pump was off by over 40%. My 8 psi reading was only 4.5 psi. It's a small, hard to read, inferior gauge. Being that off It was even obvious to me that my wing was on the low side. When i was testing the gauges it was NOT on a wing (that would not give a good reading and not relevant to the accuracy gauges) i used a small sealed canister/tank to pressurize. All gauge were attached to the tank at the same time [/b][/b]
 :)

Dwight,   You might want to try a Oil filled vacuum gauge. The oil fill gauges we use on our commercial aquarium systems last 5-10 X longer than the non oil filled (air filled). I usually get about 5 years out of them under constant water pressure where the non oil gauge don't make it a year. I'd guess corrosion is the main culprit killing gauges life. In the atmospheric controlled environment at Delta our large analog gauges were over 30 years old, calibrated ( Verifying accuracy) about every 6 months. When we finally switched over to digital accuracy improved accuracy a good amount, more than it needed to be for the FAA, but those old analogs were still working pretty good when we got rid of them.


 
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