| (a) Velocities.
(1) A force main must be a minimum of 4.0 inches in
diameter, unless it is used in conjunction with a grinder pump station.
The executive director may approve pipes with a diameter less than
4.0 inches where grinder pumps are used, on a case-by-case basis in
writing.
(2) For a lift station with two pumps, the minimum
velocity is 3.0 feet per second with one pump in operation.
(3) For a lift station with three or more pumps:
(A) the minimum velocity in a force main is 2.0 feet
per second with only the smallest pump operating at full speed; and
(B) a minimum flushing velocity of 5.0 feet per second
or greater must occur in a force main at least twice daily.
(4) The engineering report must certify that a pipeline
with a velocity greater than 6.0 feet per second can withstand high
and low negative surge pressures in the event of sudden pump failure.
(b) Detention Time.
(1) Force main detention time calculations must be
included in the engineering report.
(2) Force main detention time calculations must be
performed using a range of flow rates that represent the flows expected
to be delivered to a force main by an upstream pump station during
any 24-hour period.
(c) Water Hammer. A force main design must include
effective surge control measures to manage pressure due to water hammer
that may exceed the working strength of a force main pipe.
(d) Connection to Gravity Main.
(1) A force main must terminate at a collection system
manhole or at a manhole or preliminary treatment unit at a wastewater
treatment facility.
(2) The discharge end of a force main inside a manhole
must be restrained to prevent movement and must produce non-turbulent
flow.
(3) A collection system receiving wastewater from a
force main must be designed to accept the maximum pump discharge from
the force main without surcharging.
(e) Pipe Separation. A separation distance between
a force main and any water supply pipe must meet the minimum separation
requirements established in §217.53(d) of this title (relating
to Pipe Design).
(f) Odor Control.
(1) A force main must terminate such that the flowline
of the force main entering the manhole matches the flowline of the
gravity pipe leaving the manhole.
(2) A force main must be designed to abate anticipated
odor. An owner shall implement odor control measures necessary to
prevent a collection system from becoming a nuisance.
(g) Air Release Valves in Force Mains.
(1) Any high point along the vertical force main alignment
must include an air release valve or a combination of air release
and air vacuum valves.
(2) An air release valve must have an isolation valve
between the air release valve and the force main.
(3) An air release valve must be inside of a vault
that is at least 48 inches in diameter and has a vented access opening
of at least 30 inches in diameter.
(4) An air release valve must be made of corrosion-resistant
material.
(h) Valves. A force main must have valves spaced at
no more than 2,000 foot intervals to facilitate initial testing and
subsequent maintenance and repairs.
(i) Fatigue Life. The engineering report must include
calculations that show the strength of the force main pipe at the
end of the 50-year design life. The calculations must consider the
fluctuations between a pressurized and depressurized operating state.
(j) Alignment Changes.
(1) Bending a segmented pipe is prohibited, unless
the pipe joints are welded or heat-fused.
(2) Force main alignment changes must be accomplished
using manufactured bend fittings.
(3) Force main pipe joints must include mechanical
joint restraints or thrust blocks at all bends unless pipe vibration
calculations justify the absence of a joint restraint or thrust block.
|
