Non-condensable gasses:

Condensers generally have a series of baffles which redirect the steam to minimize direct impingement on the cooling water tubes. A bottom area of the condenser is the hotwell, as displays in Figure. This is whereas the condensate collects and the condensate pump takes its suction. Vacuum will decrease and the saturation temperature at which the steam will condense increases if noncondensable gasses are permitted to build up in the condenser.

Non-condensable gasses also blanket the tubes of the condenser, therefore decreasing the heat transfer surface area of the condenser. That surface area could also be decreased if the condensate level is permitted to rise over the lower tubes of the condenser. A decrement in the heat transfer surface has the similar effect as a reduction in cooling water flow. A reduction in the effectual surface area results in difficulty managing condenser vacuum if the condenser is operating near its design capacity.

The temperature and flow rate of the cooling water by the condenser controls the temperature of the condensate. That in turn controls the saturation pressure (vacuum) of the condenser.

To prevent the condensate level from rising to the lower tubes of the condenser, a hotwell level control system might be employed. Varying the flow of the condensate pumps is one technique used to accomplish hotwell level control. A stage sensing network controls the condensate pumps pump or speed discharge flow control valve position. Other method employs an overflow system which spills water from the hotwell while a high level is reached.

Condenser vacuum should be managed as close to 29 inches Hg as practical. This permits maximum expansion of the steam, and thus, the maximum work. It would be necessary only to condense the steam and remove the condensate to create and maintain a vacuum if the condenser were perfectly air-tight (no air or noncondensable gasses present in the exhaust steam). A sudden reduction in steam volume, as it condenses, would manage the vacuum. Pumping the water from the condenser as fast as it is established would manage the vacuum. It is, therefore, impossible to avoid the entrance of air and other noncondensable gasses within the condenser. Further a few methods must exist to initially cause a vacuum to exist in the condenser. This requires the use of an air ejector or vacuum pump to build and help manage condenser vacuum.