HI guys for some reason my pump doesn't seem to be pulling full vaccum, the flow indicator has stopped spinning but the gauge isn't quite at -30

You could have a sticking gauge or sealing problem at the catch pot.

I've gone all over the catch pot, it's not dropped vaccum over the last hour? 

Analogue gauges are quite inaccurate. If you connected a digital vac gauge you would likely find you are at full vac. The easiest way to tell is the tone of your pump, it's very easy to hear when the pump isn't under load any more and you will quickly learn the sounds of your pump. 

As Hanaldo said, pretty soon you'll not need to rely on the spinning indicator, as the absence of any crackling from the pump should tell you when no more air is being drawn through it

You might also find slight differences in your gauge reading depending upon the atmospheric conditions

Thanks for the replies I thought the tone of the pump had changed but thought I'd ask to make sure 

You also might want to check if your needle is still properly fixed to the pin. Mine came loose after multiple times degassing and swirling the pot around to pop the bubbles. Had the same issue and when I removed the plastic cover it appeared the needle slipped on the center pin. Fixed it with a tiny drop epoxy.

Hi Mattin,

Definitely doesn't look like something to worry about here: these are notscientifically calibrated gauges and should be used as a guide not a precisioninstrument.

Atmospheric pressure changes from day to day enough to mean that in differentconditions the needle might read slightly under 100% vac and then even slightlyover.

Even if you use the glycerine filled gauges that Fred's talking about then thiswill still be the case; glycerine is in there to stop the needle bouncing insituations where the pressure oscillates (not the case when you have acatch-pot acting as an air receiver) which can make the needle difficult toread. Glycerine filled gauges are much less prone to damage though andso are certainly not without merit.

Sometimes, you'll also find that you get a tiny amount of 'stiction' on theneedle and a gentle tap on the gauge can re-correct the needle slightly.

Anyone, the bottom line is that if you're ready about 99% on a basic gauge andyour project is holding vacuum then you're good to go.

All the best, Matt

Matt Statham
Easy Composites / Carbon Mods - Technical Sales

Thanks for that Matt