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Old 02 July 2020, 04:00   #1
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Pressure gauges

Morning all.

Been boating some years and never carry a pressure gauge with with on the boat, just the pump

As I'm using my Honwave T38 more I want to carry a pressure gauge so I can check the pressure quickly.

I'm a bit confused about hand held gauges, how do they check the pressure inside the tube is the don't push against the release valve? Without pushing the pin down, how do they get a pressure reading?

With a pump you get a reading on the gauge as you force the air in opening the diaphragm. But a hand held guage can't do this.

Maybe I am missing something
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Old 02 July 2020, 04:08   #2
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https://www.amazon.co.uk/Samfox-Pres...%2C143&sr=8-10

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Old 02 July 2020, 04:18   #3
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Originally Posted by Dydigital View Post

I'm a bit confused about hand held gauges, how do they check the pressure inside the tube is the don't push against the release valve? Without pushing the pin down, how do they get a pressure reading?

With a pump you get a reading on the gauge as you force the air in opening the diaphragm. But a hand held guage can't do this.

Maybe I am missing something
They *do* press against the valve to release the air. No other way to check if they don't do this.
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Old 03 July 2020, 03:59   #4
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My honwave T38 came supplied with a pressure gauge you connect to the valve. It does release a bit of air so you will lose pressure the more you test it.

An interesting point is that I have two electric bravo pumps (BTP 12 and GE 12). When these pumps cut off when the desired pressure is reached, and I double check with the honwave pressure gauge it displays a noticeable lower pressure than what the pumps think. Don't know which to believe.
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Old 03 July 2020, 07:58   #5
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Neither probably!

Make one that will be very accurate (any excuse to post this old link ):

https://www.rib.net/forum/f50/adapti...sib-42375.html
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Old 03 July 2020, 09:48   #6
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An interesting point is that I have two electric bravo pumps (BTP 12 and GE 12). When these pumps cut off when the desired pressure is reached, and I double check with the honwave pressure gauge it displays a noticeable lower pressure than what the pumps think. Don't know which to believe.
The act of compressing the air causes an increase in temperature. The heat then rapidly dissipates, causing the pressure to drop. (As air gets hot it tries to expand. If it's in an enclosed space, the pressure rises. As it cools, it contracts and the pressure drops.)

On the whole, I'd be more inclined to believe the second reading on a dedicated gauge than the initial reading on a gauge built into the pump, which is likely to be "only a guide".
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Old 03 July 2020, 10:23   #7
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>>> it displays a noticeable lower pressure than what the pumps think. Don't know which to believe.

How much lower... noticeable isn't always crucial??
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Old 03 July 2020, 12:35   #8
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The tubes inflated to 0.25bar on the pump usually read about 0.2 bar and the air floor at 0.8bar is usually about 0.5 bar on the gauge.

The tubes feel ok but i tend to have to overinflate the floor abit. It doesnt affect the boat performance that much
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Old 03 July 2020, 14:40   #9
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The tubes inflated to 0.25bar on the pump usually read about 0.2 bar and the air floor at 0.8bar is usually about 0.5 bar on the gauge.

The tubes feel ok but i tend to have to overinflate the floor abit. It doesn't affect the boat performance that much
So you're losing 20% of your positive pressure on the main tubes, and a bit more on the keel, which is the bit that is most exposed to the cold water.

I say 20% of your "positive pressure". However, you have to allow for the fact that when your pump shows 0.25 bar, there is enough air in the tube to fill it 1.25 times. All of that air is shrinking until there is only enough to fill it 1.2 times. The contraction is therefore about 4% which is well within the bounds of the effects of a temperature change.

Worry not. Inflatables are surprisingly robust. Unless you're after ultimate performance or going into extreme conditions, the boat will cope happily with this sort of variation. The pressure will vary that much on a summer's day.
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