1. (a) Velocities.

   1. (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. (2) For a lift station with two pumps, the minimum velocity is 3.0 feet per second with one pump in operation.

   3. (3) For a lift station with three or more pumps:

      1. (A) the minimum velocity in a force main is 2.0 feet per second with only the smallest pump operating at full speed; and
      2. (B) a minimum flushing velocity of 5.0 feet per second or greater must occur in a force main at least twice daily.
   4. (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.

2. (b) Detention Time.

   1. (1) Force main detention time calculations must be included in the engineering report.
   2. (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.
3. (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.

4. (d) Connection to Gravity Main.

   1. (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. (2) The discharge end of a force main inside a manhole must be restrained to prevent movement and must produce non-turbulent flow.
   3. (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.
5. (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).

6. (f) Odor Control.

   1. (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. (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.

7. (g) Air Release Valves in Force Mains.

   1. (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. (2) An air release valve must have an isolation valve between the air release valve and the force main.
   3. (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. (4) An air release valve must be made of corrosion-resistant material.
8. (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.
9. (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.

10. (j) Alignment Changes.

    1. (1) Bending a segmented pipe is prohibited, unless the pipe joints are welded or heat-fused.
    2. (2) Force main alignment changes must be accomplished using manufactured bend fittings.
    3. (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.

Source Note:The provisions of this §217.67 adopted to be effective August 28, 2008, 33 TexReg 6843; amended to be effective December 4, 2015, 40 TexReg 8254.