Heating, Ventilation and Air Conditioning (HVAC) systems keep the environments of houses, buildings and vehicles bearable. Often these systems maintain temperature and humidity by heating and cooling water. When steam returns to water it is called "condensate" and the steam-to-water part of an HVAC system is called the condensate loop. The pump that moves condensate back from the condensate loop into the rest of the HVAC system is called the condenser water pump.
Condensate Pump Basics
Condenser pumps do not run continuously. They are usually connected to a tank into which steam condenses into water. There is a float in this tank that tells the condenser pump when to turn on and when to turn off. When there is enough water in the condensation tank (the float is high enough) the pump turns on. When there is very little water in the condensation tank (the float is low) the pump turns off. Some tanks have two floats or a single float that registers two levels. At the first level the pump starts, but the second level is reached and the entire HVAC system is closed down. When the second level is reached it means something is blocking the functioning of the condenser water pump.
Nonreturn Condensate Pumps
Usually condenser pumps return water to the HVAC system, but there are occasions where this is not desirable. For example, there may be only a small amount of condensate--enough to be a problem but not enough that its recovery was really needed by the system--and it would be better for the system if it were simply expelled. Nonreturn condensate pumps for small quantities may not have a storage tank of their own, they may simply have a float in a condensation tray. Another reason for nonreturn condensate pumps is that sometimes the condensate from furnaces becomes increasingly acidic over time and would eventually pose a problem for the boiler. Nonreturn condensate pumps have a special problem: the tube that expels the water must not become clogged or the system will not work. Because the expulsion system is to the outside world it can become clogged with dirt. In cold environments it is important that the expulsion tube not retain any water, because if it freezes, that can block the tube.
Deaereating Condensate Pumps
Deaereating condensate pumps are used In a large steam power plants. They are often found on large ships like ocean liners or military war ships. The system is designed to remove dissolved oxygen from the condensate. These systems always have two pumps. The output of the condensate pump supplies input to the feedwater pump, which sends the water back to the boiler to start the cycle all over again. The two pumps working together prevent cavitation--the formation of bubbles caused when the pressure in a flowing liquid is less that its vapor pressure. Cavitation will weaken and eventually destroy a steam-operated system. The pair of pumps working together prevent cavitation and prolong the life of the system.