Sorry shopteacher, but those transmitters won't turn a pump on and off by themselves. They will show the temp and also put out a signal (4-20ma). If the transmitter is ranged for 0 thru 100 degrees, then at 0 it would put out 4ma, at 50 degrees or 50% it puts out 12ma, and 100 degrees or 100% it puts out 20ma.
You can get trip units which you can set to say trip at 50%. Then when your RTD is a 50 degrees it will close a set of contacts that you could wire to trip a larger current relay that in turn would turn your pump on. Then your transmitter and trip unit would work as a loop and serve the same function as a house thermostat and give you on/off control of the pump.