Time is of the Essence!


I thought I would continue with the math theme, as this is the most common area of concern for folks preparing for the State Treatment Operator exam. The exam is two weeks from tomorrow, so NOW is the time to study. As I suggested yesterday, promise yourself to spend just 20 – 30 minutes each day in preparation. If you do that, I bet you’ll do just fine. But start TODAY!
Today’s formula is the second of the five formulas you need to know to be successful on the math portion of the exam. We looked at the first formula in our April 6 blog. It is very helpful to realize that each of these five formulas has one unique variable. Height — or water depth — was the unique variable for the April 6 formula; Time is the unique variable today.
The real value of these unique variables is that you can tell at a glance which formula you will need to solve a math problem. If we needed to find the depth of water in a storage tank, the Volume = Area x Height formula is the ONLY one of our five key formulas that has Height in it. So the only way to solve the problem is with this formula.
For any problem that has Time as a critical element, today’s formula is the only path to success. Like each of our five key formulas, Volume = Flow Rate x Time has three variables, so we could solve three different kinds of problems with this one equation. But Time plays an essential role in each of them.
If we have a pump or some other situation where a flow rate is known, and the duration of the pumping is known, we can calculate the total volume of water moved in this operation. A typical situation would be that we have a 100 gallon per minute pumping (flow) rate for a period of 30 minutes. During that time period, 3000 gallons (100 gpm x 30 min) were pumped.
In the second scenario, we might drain (or fill) a known volume from a storage tank while we have our stopwatch going. In this case, we could calculate the flow rate going out of (or into) the tank. Let’s say 3000 gallons left the tank in 30 minutes. The flow rate leaving the tank is 100 gallons per minute (3000 gal / 30 min).
In the third situation, we know the volume of a vessel and the flow rate of the water moving through it. Here, we can determine how long it will take to drain a tank. If the tank holds 3000 gallons and we drain it at a rate of 100 gallons per minute, it will take 30 minutes (3000 gal / 100 gpm) to drain the tank.
As with all of our math problems, an essential precaution for you to take is to match your dimensions. What do I mean by this? Let’s look at the first example. If our flow rate is 100 gallons per minute and our pumping time is 30 hours, we wind up with a lot more water, don’t we? If the flow rate is gallons per minute, the Time must be in minutes — not hours, or seconds, or days.
This Flow Rate formula — or Time formula, if you prefer — is used very frequently on the Treatment test. For most treatment processes, the time that water spends in that process — the “Detention Time” — is very important to process performance. So expect to see many problems that use today’s formula.
I will be away from this blog over the weekend and on Monday, but I expect to be back next Tuesday. May 1 is tomorrow, and that means the final snow surveys of the season will be recorded. I’ll update you next week.

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