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Old 12-13-2013, 03:52 PM   #11
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Originally Posted by Michiel View Post
Your vacuum doesn't increase by a digital gauge. Its easier to monitor your vacuum but it isn't necessary. It does make the job easier.
Absolute pressure readings see the actual pressure of the day so to speak. From one day to the next, inputs such as barometric can offset the reading on an analog gauge or standard gauge reading.

With a Absolute pressure reading your able to know what is real from one day to the next without assumptions that your laminate and pump are as deep in hg as required.

Perhaps Cliff from Vacmobiles can chime in and make it more clear than I?
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Old 12-14-2013, 12:34 AM   #12
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Originally Posted by Worldwealth View Post
Absolute pressure readings see the actual pressure of the day so to speak. From one day to the next, inputs such as barometric can offset the reading on an analog gauge or standard gauge reading.

With a Absolute pressure reading your able to know what is real from one day to the next without assumptions that your laminate and pump are as deep in hg as required.

Perhaps Cliff from Vacmobiles can chime in and make it more clear than I?
Yes I know, but a gauge isn't going to change your deepest vac. You can see the actual difference but you can't pull more vac then your pump can handle.
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Old 12-14-2013, 05:46 PM   #13
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Yes I know, but a gauge isn't going to change your deepest vac. You can see the actual difference but you can't pull more vac then your pump can handle.
Correct, the form of gauge will not increase your pumps maximum vacuum. But the original poster is asking if going by Absolute pressure helps and the answer is Yes if you like to know your true vacuum.

An absolute vacuum gauge will also benefit you when used to test your vacuum pump to see if the oil is in need if changing or general seal condition.

Analog gauges are are at best a roughing test.
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Old 12-15-2013, 12:39 AM   #14
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But the ts hasn't told us what his pump is. So we don't know if it even can reach an absolute pressure. Thats why I asked for the pump, but he didn't mention it. You also have a big difference in analog gauges, there are quility ones that are more accurate then a lot of digital ones. But I totally agree it's better and easier to use a digital, but it isn't necessary.
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Old 12-15-2013, 09:51 AM   #15
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But the ts hasn't told us what his pump is. So we don't know if it even can reach an absolute pressure. Thats why I asked for the pump, but he didn't mention it. You also have a big difference in analog gauges, there are quility ones that are more accurate then a lot of digital ones. But I totally agree it's better and easier to use a digital, but it isn't necessary.
The main point here, I believe, isn't whether his pump CAN reach 29.92 inhg or not, but what is his pump ACTUALLY is delivering from day to day?

Michael says it isn't needed. I choose to say it is for my needs/requirements and consistant outcome and timing.

I have three Wallace & Tiernan absolute analogue gauges that I'm about to phase out simply due to the need to re-calibrate somewhat often at $250.00us a pop! When they were spot on, non of the myriad of cheaper gauges were correct or consistant.

I'll retire them all for roughing gauge read out only.

I'm going to try and replace them with digital which does not require re-cal because of its newer type of sensor.

I guess the less important the required duplicate result, the less accuracy comes into play.
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Last edited by Worldwealth; 12-17-2013 at 10:47 AM.
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Old 12-17-2013, 10:27 AM   #16
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Congratulations for being a glider pilot ........ aah and for the beautiful porsche as well ........... umbelievable craftsmanship .....
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Old 12-24-2013, 11:48 PM   #17
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With regard to absolute pressure gauges and the reasons for using them for infusion type applications, please feel free to check out the following technical notes: http://www.vacmobiles.com/absolute_pressure.html and http://www.vacmobiles.com/vapour_pressure.html.

Note that water vapour can be a significant cause of voids in high quality composites. Without a good quality absolute pressure gauge you will not be able to detect this problem.

For further information, please email me: info@vacmobiles.com
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Old 01-06-2014, 05:52 AM   #18
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Default Absolute pressure gauge

With an absolute pressure gauge you can check if your vacuum pump is able to reach the vacuum level necessary to perform a high quality infusion which should take place in an absolute pressure range below 20 mbar (or 0.59inHG). In regards to the discussion above I`d like to give some further information. Relative pressure measured by a standard analog dial gauge (manometer) is the pressure difference between the atmospheric pressure (which is affected by changing environmental conditions such as weather or altitude) and the in-bag pressure. This pressure difference is the force which pushes the resin into the laminate. The greater the pressure difference the greater the distance resin is able to travel. The absolute pressure value measured by an absolute digital pressure gauge (or barometer) reads the pressure difference between the absolute zero of pressure (perfect vacuum) and the in-bag pressure. The formula describing that is Patm = Prel + Pabs or Prel = Patm - Pabs. The greater the atmospheric pressure Patm and the lower the absolute pressure Pabs the greater the relative pressure Prel thus the driving force for the resin. Since absolute zero is fixed the absolute pressure value is not affected by changing environmental conditions which means that you know exactly what is going on inside the bag. Also with a barometer you are able to measure Patm and Pabs. A perfect vacuum for high quality vacuum infusion usually takes place in an absolute pressure range below 20 mbar (or 0.59inHG). At sea level and standard weather conditions a relative pressure gauge should read Prel = Patm - Pabs = 29.9inHG - 0.59inHG = 29.31 (or 1013mbar - 20mbar = 993mbar). The analog dial gauges, usually mounted on resin catch pots or vacuum pumps, are by far to imprecise to indicate tiny pressure changes. Another point is that the digital gauge really helps to shorten the time to set up the infusion system because it indicates in an instant and with a resolution of 1 mbar if you are successful in finding leaks.

Last edited by designbikes; 01-07-2014 at 12:50 AM.
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Old 01-06-2014, 10:19 PM   #19
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One thing to add:

I once saw a dial gauge, some 6" in diameter, which had a logarythmic scale. That was really neat. Was 1200 euro, though...
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