Air venturi question

Does the gauge on the tank measure line pressure or tank pressure, Just want to rule out the line pressure gauge dropping to 0. It should when bled of pressure. Some newer tanks have a gauge to measure both independently. Said another way, are you sure the tank is empty?? If so, and this is gonna sound like a 'duh' moment... then the tank valve isn't closing.

Not a lot of mechanical stuff in between. I did once have a tank valve handle that failed. It would screw out (open) but would spin/slip when screwing in (close).




 
The gauge on the AV tank reads tank pressure that’s why you need to put a dead head on the tank hose to check tank pressure, turn tank valve on read tank pressure, close tank valve, vent tank hose, then when you connect tank to compressor you let compressor build up pressure to match what you had in the tank and when the compressor gets to what the tank pressure was you open the valve on the tank and fill to 4500 psi then close tank valve when compressor shuts down and turn off the compressor switch and let the cooling fan run while you vent line pressure from the compressor vent on the compressor and let the cooling fan run for a few more minutes then shut cooling switch off.

Ive had my AV compressor for a year and fill both a 90ci tank and my 74cf tank and I’ve never had a issue except the one time I was turning the tank valve the wrong way and of coarse filling a 90ci tank is different then filling a 74cf tank or any big tank, I just filled my new 88 cf tank yesterday and it took 1hour 18 min from zeropsi to 4500psi.
 
Its not just the tank line emptying. It is also the compressor with the line. It sounds like a lot but it is only the backed up tank line and compressor air bleeding. Same thing i thought when i first used my av compressor and av 98 cf tank. I only bleed the compressor after shutting off the tank. It is faster and also bleeds the tank line.
 
I have a towel around my compressor bleeder valve to catch any water and contaminants that blow out, keeps the mess in the towel not all over the floor.

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Thank you all for the help provided. Chuck it up to newbie nerves.

Now I know how to use that dead head. Had me wondering why I needed the thing.

I think there are/were a few of us that suffered from the Newbie Nerve syndrome when we got our 1st tank or our 1st Compressor so your not alone and if you have questions just ask, that’s what this forum is for, better safe then sorry as they say. You should of seen how nervous I was when I tetherd my 1st tank to a external regulator then to my HMx airgun yikes, but it was so simple I just over thought it just like when I had the air flow issue with my tank when I filled it up and then vented the compressor and lost all my air, yep just being nervous and over thinking it.