Section Env-Wq 704.07 - Details of Design and Construction of Force Mains and Pressure Sewers(a) Force mains for constant speed pumps shall be sized to yield a cleansing velocity of 3 feet per second or greater at design pump capacity.(b) Force mains for variable speed pumps shall be sized to yield a velocity of 2 feet per second or greater at average daily design flow.(c) Force mains shall be 4 inches or larger in nominal diameter.(d) Pressure sewers shall be 1.5 inches or larger in nominal diameter.(e) Minimum allowable pressure sewer pipe sizes and corresponding flow rates shall be as set forth in Table 704-3, below: Table 704-3: Minimum Pipe Size and Flow Rate for Pressure Sewers
Number of Connections Served | Estimated Peak Flow, gpm | Minimum Pipe Size, inches |
1 to 3 | 15 | 1.5 |
4 to 10 | 20 | 2 |
11 to 30 | 30 | 3 |
31 to 150 | 90 | 4 |
(f) Pressure sewers for grinder pumps shall be sized to yield a velocity of 2 feet per second or greater at design pump capacity.(g) To prevent air locking, force mains shall be provided with an automatic air relief valve at each high point, installed within a manhole structure that meets the design requirements of Env-Wq 704.12 through Env-Wq 704.17.(h) Force mains shall enter the gravity sewer system at the flow line of the receiving manhole.(i) Force mains shall be provided with a drainage blow-off at each low point that: (1) Has a properly valved connection for a vacuum truck or other suitable containment device; and(2) Is installed within a manhole structure that meets the design requirements of Env-Wq 704.12 through Env-Wq 704.17, with sufficient space for handling the displaced waste without danger of pollution or health hazard.(j) Force mains shall be designed in accordance with Env-Wq 704.07, constructed with materials as specified in Env-Wq 704.08, and tested as specified in Env-Wq 704.09.(k) Pressure sewers shall be designed in accordance with Env-Wq 704.07 and Env-Wq 704.20, constructed with materials as specified in Env-Wq 704.08, and tested as specified in Env-Wq 704.09.(l) Thrust blocks made from inorganic, corrosion-resistant material shall be placed at all bends, elbows, tees, and junctions.(m) Force mains shall be designed to withstand instantaneous hydrostatic pressures of at least 2.5 times the design total dynamic head or at least 100 psi, whichever is greater.N.H. Admin. Code § Env-Wq 704.07
(See Revision Note at chapter heading for Env-Wq 700) #8590, eff 3-25-06
Amended byVolume XXXIV Number 46, Filed November 13, 2014, Proposed by #10693, Effective 10/15/2014, Expires10/15/2024.