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Old 16 January 2010, 11:21   #11
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OK, "druck" may be a British term....I have never heard that term before....what kind of pump is that...a low pressure water pump? What kind of application is a "druck" used for?
Drucks the make of the pump.
I wouldn't bother messing about with it to be honest. You can buy a new gauge cheaper than you could get one calibrated.
If you bounce it about then it could be out of cal again.
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Old 16 January 2010, 15:21   #12
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Just a suggestion but could both gauges be telling the truth - but giving you slightly different info. A pressure gauge is essentially measuring a pressure difference between the test side (in your case the boat) and some reference point. One of your gauges may be measuring against a sealed reference point and the other relative to atmospheric pressure. A 1 psi pressure fluctuation is consistent with atmospheric changes.
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Old 16 January 2010, 15:44   #13
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Just a suggestion but could both gauges be telling the truth - but giving you slightly different info. A pressure gauge is essentially measuring a pressure difference between the test side (in your case the boat) and some reference point. One of your gauges may be measuring against a sealed reference point and the other relative to atmospheric pressure. A 1 psi pressure fluctuation is consistent with atmospheric changes.
Wouldn't a gauge that measured between two pressures be a differential pressure gauge.
The gauge he's using will have a sealed bourdon tube in it which moves a quadrant and then the pointer.

He's using one gauge and then the other so he won't have an atmospheric pressure change over the time he's using it.
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Old 16 January 2010, 17:02   #14
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Wouldn't a gauge that measured between two pressures be a differential pressure gauge.
no all pressure gauges are measuring a pressure difference. A "differential pressure gauge" is a bit more complicated and has connections to two different systems.

However the general concept of the bourdon tube is that it measures a pressure difference between the pressure inside the tube and outside it (inside usually connected to the test system, and the outside is often open to atmosphere). It is measuring pressure relative to current atmospheric pressure. Sometimes more correctly referred to as gauge pressure, written as psig (or Barg).

But it is also possible to have a sealed environment on the otherside of the tube that contains a reference pressure (this might be a vacuum, a chosen pressure, or whatever the atmospheric pressure when the device was made and sealed), if the reference pressure is vacuum, or known, then the pressure measured can be absolute, but the scale can be 'offset' so that it appears to read gauge pressure.
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Old 16 January 2010, 17:23   #15
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no all pressure gauges are measuring a pressure difference. A "differential pressure gauge" is a bit more complicated and has connections to two different systems.

However the general concept of the bourdon tube is that it measures a pressure difference between the pressure inside the tube and outside it (inside usually connected to the test system, and the outside is often open to atmosphere). It is measuring pressure relative to current atmospheric pressure. Sometimes more correctly referred to as gauge pressure, written as psig (or Barg).

But it is also possible to have a sealed environment on the otherside of the tube that contains a reference pressure (this might be a vacuum, a chosen pressure, or whatever the atmospheric pressure when the device was made and sealed), if the reference pressure is vacuum, or known, then the pressure measured can be absolute, but the scale can be 'offset' so that it appears to read gauge pressure.
Thanks for explaining my own job to me, did you google the above?
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Old 16 January 2010, 17:50   #16
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Thanks for explaining my own job to me, did you google the above?
nope
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Old 17 January 2010, 20:20   #17
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Inside a Pressure Gauge

Being a pressure gauge fan, thought that buying more expensive suppossed state of the art gauges will give precise readings, will not mention brands, although bigger, more accurate and easy to read than small ones, some can have up to 0.5 psi innaccurracy differences. It's a real shame that manufacturers don't pass a strict a lab test before sending units to clients.

The only way to test accurracy would be to buy 2 of the same brand, inflate an air mat, keel to 3.0 PSI with one and test the other and compare readings. Opting for rocket science and having lot's of gauges, went to a digital pressure lab, a tank was filled with controled 3.0 psi, tested 3 different gauges one of them read 3.0 exact, it's the master gauge, now can compare the reading of any gauge that will be given with sibs/ribs to the master reading and see their + / - 3.0 psi innaccurracy.

Most of the inflatables gauges on the market uses burdon tubes for measuring air pressure, the problem is located where the tube is solded to the gauge body, the slightest tube angle innaccurate left/right soldering position will give innaccurate readings, see pic for understanding.

Happy Sibbing
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Old 17 January 2010, 22:28   #18
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Thanks for explaining my own job to me, did you google the above?
I bet Polwart subscribes to pressure gauges monthly, though the reply does look very "Googled".
Polwart knows everything about everything dont you know, he would have put the Oracle at Delphi to shame..........
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Old 18 January 2010, 04:28   #19
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It's a real shame that manufacturers don't pass a strict a lab test before sending units to clients.
if you need accuracy you buy a calibrated gauge (or pay someone to calibrate it) if you need a pressure indication then this is probably wasted money; if I remember rightly you were promoting gauges which cost less than 10 dollars.

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The only way to test accurracy would be to buy 2 of the same brand, inflate an air mat, keel to 3.0 PSI with one and test the other and compare readings.
won't really tell you anything about accuracy though. it will simply show that either the two gauges disagree (which is more accurate ?) or that they agree (but both may be innacurate by the same amount) - you need to compare to a calibrated gauge if you want to understand accuracy.
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Old 18 January 2010, 04:33   #20
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I bet Polwart subscribes to pressure gauges monthly,
I seem to have missed that one from my subscriptions list... ...but I did used to read "vacuum and coating technology" for a while.
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