Turning the crank on the Heat Pump exhibit pumps heat from one copper coil to another. Visitors crank a small refrigerator compressor and compare the temperature of the two coils, one hooked to the high pressure output of the compressor, the other to the low pressure input. As more work is done, the high pressure coil becomes warm and the low pressure coil becomes cold. Leakage from the high pressure side to the low pressure side can be regulated with a valve.