The functions of a pressure tank are to:
(1) protect and prolong the life of the pump by preventing rapid cycling of the pump motor;
(2) provide water under pressure for delivery between pump cycles; and
(3) provide additional water storage under pressure to assist the pump in meeting the total demands of a system if the pump or well is incapable of supplying the required capacity.
Selecting a Pressure Tank
When selecting a pressure tank, certain information must be known:
(1) system demand;
(2) pump capacity; and
(3) well capacity.
The system demand is a function of water usage and location, expressed as gallon(s) per minute (gpm) and pound(s) per square inch gauge (psig), respectively. Usage or flow (gpm) can be determined using one of several methods (refer to Table IV.1.1 for typical demands):
a) The fixture method determines the system demand by totaling the number of fixtures in the home, including outside hose bibs, and multiplying this number by 1 gallon per minute (gpm). For example, 10 fixtures x 1 gpm = 10 gpm.
b) The peak demand method determines system demand considering that more than one fixture will be in use under peak demand. The number of fixtures being used at the same time is determined and multiplied by 3 gpm. For example, 4 fixtures x 3 gpm = 12 gpm.
c) An alternate method determines system demand by calculating the number of bathrooms (half baths are considered as 1) and multiplying by 4 gpm. For a home with 2 � bathrooms, multiply 3 x 4 gpm = 12 gpm.
Use the largest system demand determined by the above methods.