Current through August 31, 2023
Hydropneumatic tanks use compressed air to regulate pump
cycling and to absorb pressure surges (water hammer). These tanks do not
provide true storage. Systems serving more than one-hundred-fifty (150) homes
are generally better served by providing reservoir storage, as set forth in
Sections 544,
545 and
546. (3-24-22)
01.
General Design of Hydropneumatic
Systems. (3-24-22)
a. Tanks shall be
located above normal ground surface and be completely housed.
(3-24-22)
b. Tanks shall have
bypass piping to permit operation of the system while the tank is being
repaired or painted. Exterior surfaces and accessible interior surfaces shall
be provided with protective coatings and shall be maintained in good condition.
Supports beneath tanks shall be structurally sound. (3-24-22)
c. Tanks shall 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 systems 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. (3-24-22)
d.
Tanks of greater than one-hundred twenty (120) gallons volume shall conform
with the American Society of Mechanical Engineers (ASME) specifications code
for unfired pressure vessels. Tanks of less than one hundred twenty (120)
gallons volume shall meet the ASME code or be certified by a nationally
recognized testing agency to be capable of withstanding twice the maximum
allowable working pressure. (3-24-22)
02.
Requirements Specific to
Conventional Hydropneumatic Tanks. Conventional tanks are those that
have a direct air to water interface and require periodic air recharge to
compensate for absorption of air into the water. (3-24-22)
a. Each tank shall 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 shall be at
least twenty-four (24) inches in diameter. (3-24-22)
b. The gross volume of tanks in systems
served by variable speed pumps may be less than that required for systems
served by constant speed pumps. Design volumes shall be approved by the
Department on a sitespecific basis. (3-24-22)
03.
Requirements Specific to Bladder
Tanks. Bladder tanks have a membrane that separates air and water inside
the tank. (3-24-22)
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 system).
(3-24-22)
b. Each manifold assembly
shall have a pressure gauge and pressure operated start-stop controls for the
pumps. (3-24-22)
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 systems
served by variable speed pumps shall be approved by the Department on a site
specific basis. (3-24-22)
