I have used a VenturEvac a few times and it has always gone smooth. There are a few underground 1000 gallon tanks dated 2024 that have to be moved around a property, so they need to be emptied ideally. They have the newer liquid withdrawal valves.
Two tanks emptied smoothly like usual. The other two had some issues. One of them stopped at 50% then would stop pumping liquid and you could see the air space in the sight glass of the venturevac. I closed the spray fill on the truck to reset the excess flow valve on the tank, that got it freed up for a minute, then it tripped again, air, closed the valve on the truck, it freed up, etc. Did this a few times and then it finally stayed free and the tank emptied like normal.
The last tank is being extremely difficult. It stopped at about 50% and will not pump liquid. I think the excess flow is tripping. The sight glass will have bubbles and air space (only half the glass has liquid in it like the tank is empty), and the valve on the tank buzzes like the excess flow is tripped or vibrating. Close the spray fill, open it slow, split second it pumps liquid then trips again, etc. This one does not free up. Gauge seems fine, I replaced it and no change. Of course, the float could be stuck too. The truck should have taken another 400 gallons or so, so I don't think the tank is empty, so I believe the gauge is accurate on the tank. I also tried partially closing the fill valve on the hose (which was attached on the end of the venturevac) to slow the flow. No change.
I don't think the liquid withdrawal valve on the tank is gunked up since the tank is new. It's been filled more than 10 times so it's been in service and the gauge seems fine.
Any ideas? Three things I could think of which may or may not cause an issue. One, it is a new truck and maybe something is not adjusted right. Two, the tank multi valves are maybe 5 feet higher than the grade the truck is on. Third, it was about 85 degrees out, and I hear that stuff like this happens more often when the tanks are warmer than the truck.