the right hand side of the sheet in solid lines such a layout may be found in the nfpa engine driven fire pump manual in fig3 engine 30 is represented with a cooling pump 32 which is driven directly from the engine and is built into the engine the cooling loop contains the engine coolant which generally will be an ethylene glycol water mixture and the coolant circulates through the water cooled tube and shell heat exchanger 33 where its heat is discharged as the coolant is circulated in coolant tubes inside the heat exchanger water from the primary water supply line 34 which is water shunted or tapped off the discharge from the fire pump 36 as it is being driven by the engine this water circulates around the coolant tubes and is dumped down the drain 35 rather than being recirculated the fire pump 36 may supply water directly to fire hoses to put out fires and also may provide additional sprinkler system water usually this source of water is from the municipal water supply and as the fire pump is turned on in response to an emergency the automatic valve 37 is opened indicating valves 38 and 42 are to be open at all times so that when the fire pump begins operation and is driven by the engine the automatic valve 37 opens by a signal from the fire control panel so that water will flow through the line 34 to the heat exchanger 33 the water that flows though valve 38 at this time has also traveled through union 46 strainer 47.