mystery with gauge GDH 200-14

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#1

Today, I wanted to make an integrity test over a little crack I have in one mold wich did not look very suspicious, I made a small square bag that could cover the crack sealed and pulled vacuum, much to my surprise, my brand new Greisinger GDH 200 14 showed a very small drop, it took 3-4 minutes to show the next number in the absolute pressure reading, after trying to improve the seal of the small square bag, just to get the same pressure drops, I isolated with two very reliable clamps the piece of vacuum tube that only contained a T connector and the gresinger gauge, and much to my surprise, it showed the same very small vacuum drop proving in my opinion that the gauge itself was the cause of the leak :confused:¿¿¿???

Can this be possible, that the absolute pressure gauge produces (or needs it do its job) a small leak ???

I repeated the experiment with the gauge connected straight to a tube going to the vacuum pump and after vacuum pulled, clamped the tube 2 meters away from the gauge leaving then just the gauge with two meters of tube under vacuum and again got the same results, so it has to be the gauge …

I was expecting off course, the gauge to show almost unlimited vacuum retention for a long while in such an absolutely simple set up.

Has anyone else seen this happening, it would certainly suprise me for this to be normal behaviour of the gauge …

#2

It is possible your clamp doesn’t clamp off completely. It is hard to clamp off 100% and maybe impossible. This depends on the clamp and the hose.

#3

My Clamps are all DD compound´s clamps, they where very strongly closed, well aligned with the tube and I very much doubt they could be the reason for the leak, but I will not say, your theory is impossible …

but I would also find impossible that a gauge made for measuring low vacuum levels could introduce a leak by itself, unless off course the gauge is faulty, something that would also be hard to believe because it is made by a reputable german manufacturer and is what many professionals use …

#4

I am sure it are not the clamps, if they are closed they are closed :smiley: Or have you closed them to hard that you damaged te hose?
Most times I had that it was the connection to the Greisinger, seal it with tacky. Also the connectors can be the reason, seal them also with tacky. If it is still there it may be the bagging film or the tacky tape. Long time ago I had a tacky tape that was not completely airtight.

#5

I already had done that, packing with tacky yellow tape all the joints, so I believe is the Greisinger unit that came faulty from factory, I only had it for maybe one month …

#6

Did you change the hose? I have 15mm thick foam glued enveloping mine after dropping it twice the first day I got it :slight_smile: oops… great value…

#7

I can not believe that it is the Greisinger, but nothing is impossible. Check it just with a piece of hose connected to the vacuum pump and than clamp the hose.

#8

I will try that today, but a dutch friend told me that he has seen a few units that leaked …

#9

Haven’t had any problems with mine. My first guess would be the hose tail on the meter might be damaged or not sealing.

#10

Hi ASB, the connecting hose with the gauge is new, and it was sealed from the outside with tacky tape … the loss, is not much, today we measured it after clamping some 20 cm of 10 mm hose that connected to the thinner one that connected to the gauge, it needed in that conditions 15 minutes to loose 4 mb of vac.

It is not that the gauge is unusable, it does provide very accurate measures and we all like it, but considering its price and purpose in my opinion should not have any leak of any kind,

We still can cover the thin hose that goes to the gauge with some tacky as well, just to cover the rare even of this hose having the leak …

I will do that and post the results here …

#11

I’m having the same problem since it was new. Any suggestions?

#12

Yes, send it back. I bought one myself and had the same problem, leaking. Sended it back and never bought a new one.

#13

We have about 15 of them and no one has that problem. What I am wondering, if you clamp direct to the gauge I can understand that maybee a very small leak can have an effect, but even on a small part you should not realize a pressure drop then because the volume is much bigger. What it can be is moisture that starts to vapourize, the pressure drop will then stop at about 20mbar. But you will always have gas diffunding through your materials.

#14

Are there other brands someone could suggest me to buy?

#15

Testo has a absolut pressure gauge too.

#16

Dominik, could you please explain the process of the vaporizing moisture?
Thanks.

#17

Vacmobiles explains it well: http://www.vacmobiles.com/vapour_pressure.html

#18

NOW it’s all clear to me! Yesterday the pump has been pumping the air out from the bag as normal until (as soon as the bag begun to tighten) I had a sudden increase of absolute pressure and less pumping action. Just as I got a puncture on the bag. I then inflated the bag (it was a small one) with compressed air to check for leaks, but I discovered the bag was OK.
The link explained me perfectly what happened. Thanks a lot.