Discrepancy between tank volume and sales amount

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oldnewbie
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Discrepancy between tank volume and sales amount

Post by oldnewbie » Sat Feb 15, 2020 6:26 pm

Hi;

I have a station where I regularly see a difference of 50-100 gallons/day between the amount of sales recorded by my Commander, and the difference in volume reported by my Veeder-Root. In other words, 50-100 gallons/day seems to be disappearing. I'm looking at gross volumes, not net. I see this both in the summer (which I expect, due to volume shrinkage as the gasoline cools in my UST's), and in winter, which I don't expect, since the delivered gas is typically cold, and slowly warms as it sits in the UST's. I have my dispensers calibrated twice a year, and they never need much adjustment (on average, they might need to be adjusted +/- 0.1%). My site typically does 6-7,000 gallons/day. The site has double-wall fiberglass tanks and piping, with interstitial sensors monitored by the Veeder-Root. Also, many years ago, the site's UST's leaked fuel with MTBE, so there are multiple monitoring wells around the site. The measurements from these monitor wells do not show any gasoline components - just the residual MTBE. So, in short, I'm confident I don't have a leak. Until several months ago, I had Wayne Vista dispensers, and now have Wayne Ovation 2 dispensers. There seems to be no difference between the magnitude of the issue between the Vista and the Ovation dispensers.

Does anyone have any ideas on where this discrepancy is coming from, and how I can get rid of it?

ZMiller
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Re: Discrepancy between tank volume and sales amount

Post by ZMiller » Sat Feb 15, 2020 9:02 pm

Is a monthly discrepancy reading a daily loss carrying through at the end of the month? Assuming you blend mid grade is one tank over and the other short? How many shift closing per day?
When you are dead it's likely you won't know it. It could be difficult for others. It's the same if you are stupid.
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dctech
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Re: Discrepancy between tank volume and sales amount

Post by dctech » Sat Feb 15, 2020 9:12 pm

Are you using BIR, or are you going by the POS readings vs. the inventory readings

oldnewbie
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Re: Discrepancy between tank volume and sales amount

Post by oldnewbie » Sun Feb 16, 2020 11:42 am

I'm going by the POS (Commander) sales readings vs the inventory (Veeder-Root) readings. I'm seeing the shortage in the regular gas, and am not seeing a corresponding overage in my premium gas readings. My mid-grade is mixed at the dispenser, but I only sell 200-300 gallons of mid-grade a day, so it's hard to see how this small amount of sales would lead to 50-100 gallons/day of shortages.
I should clarify that I only see these large shortages on days when I don't get a fuel delivery. On days when I do get a fuel delivery (in the winter), I typically see a small (0-30 gallon) overage, which I've assumed was due to the delivered gas being cold, and then expanding slightly as it warms up in my UST.
Also, I tabulated and graphed my shortages over the last 6 weeks on days when I didn't get a delivery. The data shows a correlation between the gallons I'm selling, and the gallons I'm short. The correlation coefficient is 0.49, which means that about half of the shortages can be correlated to gallons sold.
Now that I've seen this correlation, I'm going to go back and tabulate the gallons sold for each fuelling position, and see if gallons sold at any one fuelling position has a higher correlation to the shortages than the other fuelling positions do.

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POSDiddy
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Re: Discrepancy between tank volume and sales amount

Post by POSDiddy » Sun Feb 16, 2020 5:00 pm

It would help here to get an understanding of what exactly you're looking at for comparison. Without knowing what values you're using, I'd say walk them end:end in a spreadsheet:

- Totalizer readings from each fueling position at start of day (or shift) (No one dispensing) (Direct from dispenser - not the POS)
- Tank inventory at start of day (or shift) (No one dispensing) (Direct from tank gauge)
- Totalizer readings from each fueling position at end of day (or shift) (No one dispensing) (Direct from dispenser - not the POS)
- Tank inventory at end of day (or shift) (No one dispensing) (No one dispensing) (Direct from tank gauge)

From there, if you take ending totalizers minus start totalizers (and add those all up) does that number of gallons equal the starting inventory from the tank gauge minus the ending inventory? (If they equal - great, you can now start comparing to POS reports. If those aren't even within the variance you expect, then you can at least take the POS out of the equation. One thing that is unclear is how you know for certain that the volume you are getting from your gauge is precise. If over the course of time, someone changed the tank size, tilt, etc. - even slightly - that would cause values to be slightly skewed and add up over the course of time.)

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