Hi guys, i have a bought a few meters of MTI hose and i’m told for me to get the desired results i have to make sure my system is operating @ absolute pressure and that needs a digital gauge instead of the normal analog vacuum gauge so what i need to know is , is everyone using a digital gauge during their infusion process if not what are you using to ensure that you system is @ absolute pressure.
with my pump i can only reach a max 27Hg’s and the pump is still brand new 
thanks
The gauge doesn’t change your vacuum, another vacuumpump will. The only thing is, one gauge displays more accurate then another. What kind of vacuumpump do you have and how many meters are you below or above see level ?
Hi Michiel, currently where i’m based i’m 3280 feet (1000 meters) above sea level.
Yes, a digital absolute pressure gauge is essential for vacuum infusing, and I highly recommend it. Vacmobiles sells a good one, thats what I use.
Here is one as well:
http://www.vacuumsystemen.com/toebehoren/vacuummeters/digitale-vacuummeter-1-1000-mbar.html
Which works OK, and can be used for logging as well.
Also the digital vacuum switch that I am working on displays the vacuum pressure digitally in 1 mbar increments, and probably turns out cheaper.
Look for Greisinger GDH 200-14. It is one of the cheapest and used by many professionals. I like it and use it.
I just read your dry spot thread. Have you meassured the vacuum direct at the pump? Maybe you have pores in your mould and thats why you also can not get perfect vacuum. Have you made a drop test?
Post pictures from the mistake and your pump. We will fix your problem.
Not quite sure why no one has mentioned this yet, but Vacuum is influenced by altitude. Max attainable Vacuum for 1000m is 28.9 inHg which is 96.6%.
Just so your aware of what is achievable where your located and the pump may be fine @ sea level!
Jim.
Hi DDCompound, how can i fix pores on the mold? i’m in the process of buying Greisinger GDH 200-14 and i hope it will be a worthwhile investment cos this is not cheap :(.
i will send pics later today.
I would like to know if it really is a necessary item, maybe to avoid surpassing the pressure of vapours of the resin ?? what is really its importance ? to avoid the mistakes induced by barometric pressure variations ??
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?
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.
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.
Congratulations for being a glider pilot … aah and for the beautiful porsche as well … umbelievable craftsmanship …
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
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.
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…