Force mains.

A. Force mains serving sewage lifting devices, such as grinder pumps and pump stations, shall be designed in accordance with § 257-25. Additional design requirements are:(1) Force main pipe material shall be:(a) Polyvinyl chloride (PVC) plastic pipe. Pipe shall conform to ASTM D2241. Materials used in the manufacture of PVC pipe shall meet ASTM C1784. The minimum wall thickness shall be SDR-21. Fittings shall conform to ASTM D2241. Joints and gaskets shall conform to ASTM D2241, D1869, F477.(b) Other pipe materials. Other pipe materials require prior written approval of the Commissioner of Public Works and/or Chief Plant Operator and/or Superintendent of Sewers before being installed.(2) Trenching, bedding, and backfilling shall be in accordance with § 257-30. (3) Joint preparation and assembly shall be in accordance with the manufacturer's written instructions.(4) Anchorages, concrete blocking, and/or mechanical restraint shall be provided when there is a change of direction of 7 1/2° or greater.(5) Drain valves shall be placed at low points.(6) Automatic air relief valves shall be placed at high points and at four-hundred-foot intervals, on level force main runs.(7) Air relief and drain valves shall be suitably protected from freezing.(8) When the daily average design detention time, in the force main, exceeds 20 minutes, the manhole and sewer line receiving the force main discharge or the sewage shall be treated so that corrosion of the manhole and the exiting line are prevented.

The corrosion is caused by sulfuric acid biochemically produced from hydrogen sulfide anaerobically produced in the force main.(9) The force main shall terminate, in the receiving manhole, at a PVC plastic sewer pipe T. The vertical arms of the T shall be twice the diameter of the force main. The upper arm shall be at least four feet long; the lower arm shall terminate in a PVC plastic sewer pipe 90° elbow in a flow channel directed to the manhole exit pipe. The T and its arms shall be securely fastened to the inside surface of the manhole wall using corrosion-resistant anchors.B. Force main testing.

All force mains shall be subjected to hydrostatic pressure of 150% of the normal operating pressure. The duration of the test, at pressure, shall be at least two hours. Before conducting the test, the pipe shall be filled with water and all air shall be expelled. During the test, water shall be added, as needed, to maintain the test pressure. The amount of water added shall be recorded so as to calculate leakage. Leakage shall not exceed 25 gallons per day per mile per inch nominal pipe diameter. During the test, the owner and the Commissioner of Public Works and/or Chief Plant Operator and/or Superintendent of Sewers or authorized official shall walk the route of the force main and examine the exposed pipe and the ground covering and backfilled pipe to discover leaks.

Leakage in excess of that specified above shall be corrected with new material, at the owner's expense, and the test repeated. Any observed leaks shall be repaired at the owner's expense. Each test section length shall be as approved by the Commissioner of Public Works and/or Chief Plant Operator and/or Superintendent of Sewers, but in no event longer than 1,000 feet.