Circulator or pump?

You already have circulators, and will replace with another

A circulator is a specific type of pump designed for use in closed-loop systems, primarily for moving fluids like water in hydronic heating, cooling, or hot water recirculation systems.  While technically a pump, a circulator is specialized for low-pressure, high-flow applications where the primary goal is to maintain continuous fluid movement rather than to lift fluid against gravity or generate high pressure.  Unlike general-purpose pumps that may need to overcome significant static head (elevation changes), circulators operate within a pressurized system where the fluid is already at the required elevation, so they only need to overcome friction losses in the piping. this means that you already have Taco circulator pumps that circulate water in a closed system. All circulators are pumps, however, not all pumps are circulators. here are some pumps that do not circulate and can develop much higher pressure than a circulator:

As far as changing an existing circulator pump on your system, you are often better off replacing like for like as @GGross mentioned unless someone specified an incorrect circulator pump for your needs. This does not seem to be the case here. I have often found that you can purchase a new circulator pump of the same model number, and just replace the motor housing and impeller cartridge without needing to take the pump casing off of the connected piping. This saves time and labor hours.

technically the pump at a gas station is down under ground inside the tank and the thing you see is just a meter and valve.

"Circulator" is a specialty term; I have never seen it outside the heating industry. But no matter — within the trade, everyone (pretty much!) knows what you are talking about!

I have never seen a "circulator" which wasn't a centrifugal pump — which doesn't mean they don't exist, thought I have never run into one. Like all centrifugals, they will have a characteristic pump curve which relates the pressure difference devloped across the pump to the flow through the pump, and these curves can be quite different for different models. It's necessary to be at least vaguely aware of this in choosing a particular pump.

Now where things get slightly flaky is that that curve is determined at a specific rpm. When you change the rpm, the curve moves — and this is why critters like ECM pumps can be used for a wide variety of applications, and how delta T or delta P pumps are controlled. They are all still centrifugals, but the motor rpm is changed as needed.

Back in the bad old days we did the same sort of thing with throttling valves on the output — but that wastes energy (sometimes a lot of it!), since it is quite difficult to change the rpm of a typical small to medium AC motor — and since physically commutated motors (sometimes for the old timers referred to as "universal motors" since they run equally well on AC or DC current) (which are easy to change the speed on) are a maintenance nightmare.