Section 58.01.08.547 - HYDROPNEUMATIC TANK SYSTEMSHydropneumatic tanks may be used to regulate pump cycling and to absorb pressure surges (water hammer). Hydropneumatic tanks may not be used for storage for PWSs serving more than one-hundred-fifty (150) connections unless otherwise approved by the Department.
01.Design of Hydropneumatic Systems. Tanks must:a. Be located above normal ground surface and be completely housed.b. Have bypass piping to permit operation of the PWS while the tank is being repaired or painted. Exterior surfaces and accessible interior surfaces are to be provided with protective coatings and shall be maintained in good condition. Supports beneath tanks must be structurally sound.c. Be sized to limit pump cycles to not more than six (6) per hour unless a pump manufacturer's warranty specifically supports more frequent cycling. The number of pump cycles may be increased in PWSs with multiple pumps if a means to automatically alternate pumps is provided. The Franklin Electric AIM manual, referenced in Subsection 002.02, Chapter 11 of the Washington State Department of Health Water System Design Manual, referenced in Subsection 002.02, or manufacturer's recommendations may be used as guidance in calculating the size of hydropneumatic tanks.d. Conform with the American Society of Mechanical Engineers (ASME) specifications code for unfired pressure vessels when they are of greater than one-hundred twenty (120) gallons volume. Tanks of less than one hundred twenty (120) gallons volume must meet the ASME code or be certified by a nationally recognized testing agency to be capable of withstanding twice the maximum allowable working pressure.02.Requirements Specific to Conventional Hydropneumatic Tanks. Conventional tanks are those with a direct air to water interface and require periodic air recharge to compensate for absorption of air into the water. a. Each tank must have an access manhole, a drain, and control equipment consisting of a pressure gauge, water sight glass, automatic or manual air blow-off, means for adding air that is filtered or otherwise protected from contamination, and pressure operated start-stop controls for the pumps. If tank size allows, the access manhole will be at least twenty-four (24) inches in diameter.b. The gross volume of tanks in PWSs served by variable speed pumps may be less than that required for PWSs served by constant speed pumps. Design volumes will be approved by the Department on a site-specific basis.03.Requirements Specific to Bladder Tanks. Bladder tanks have a membrane that separates air and water inside the tank. a. Bladder tanks must be pre-charged with air to a pressure of five (5) psi below the setting at which the pump turns on (the low operating pressure for the PWS).b. Each manifold assembly must have a pressure gauge and pressure operated start-stop controls for the pumps.c. The procedure for sizing bladder tanks is to determine the number of a selected size of tanks that are needed to provide pump protection. Reduced tank volume in PWSs served by variable speed pumps will be approved by the Department on a site-specific basis.Idaho Admin. Code r. 58.01.08.547