Help With Zefon Air Sampling Pump?

I recently had all my mold inspection stuff stolen out of my vehicle. I bought a new/used pump on Ebay(see picture) and it seems to run great, however, it doesn’t want to go all the way to 15psi. I can twist the pressure knob and make the pressure/suction drop down to nothing but then when I twist it to go back up, it always stops at 10psi.

I really don’t want to waste the time or money on sending it back if there’s a way I can fix it myself.

Has anybody ever run across this problem? Is it possibly an adjustment setting causing it to stop at 10psi or is it some sorta defect within the pressure gauge?

The pump didn’t come with any directions or pump settings info so I was wondering if any of you might have some experience with these pumps?

Problem solved…

I took some parts of the pump apart and found that the little brass 90 degree elbow had some debris trapped in it. No matter how much I turned the pressure up, only 10psi was able to get past the elbow. It’s all cleaned out and sucking like a new vacuum cleaner.

The o ring on the back of the meter can go bad as well.