There shall be two identical pumps, one of which is a standby, and each pump shall be capable of handling the maximum flow. The pump-motor units shall be of the submersible nonclog or the submersible grinder type, close-coupled, extra heavy duty units, designed to pump raw sewage.
A mixed-pair arrangement consisting of a submersible nonclog pump and a submersible grinder pump is prohibited.
The submersible nonclog pump shall be capable of passing three-inch-diameter solids. The impeller shall be dynamically balanced. The cutter and/or cutting implement(s) for submersible grinder pumps shall be made of hardened stainless steel.
Although low speed pumps (1,800 rpm and below) are generally preferred for the sake of reducing wear and extending bearing and seal life, higher rpm pumps are acceptable when there are no low speed pump alternatives available.
The motor shall be suitable for continuous duty with moisture resistant, Class F insulation rated for a minimum 55°C temperature rise. The motor shall have a minimum service factor of 1.25 for one-half to one horsepower motors, and a minimum service factor of 1.15 for motors rated above one horsepower. Power and signal cables shall be of the SO type construction suitable for submersion in sewage and of adequate length. Strain relief shall be provided at each entry into the pump unit. The cables shall be provided with cable supports of the wire braid sleeve type with attachment tails for connection to the access hatch frame.
The pump shall have two mechanical seals at the impeller shaft to prevent water from entering the motor. The pump units shall be equipped with moisture sensors to indicate water leakage beyond the lower mechanical seal. The pump units shall also be provided with bimetallic heat sensors embedded in each phase winding of the motor (normally closed contacts) connected in series with leads brought out. The moisture sensor (through a relay) and the heat sensors shall be wired to the pump control circuitry for protection.
The pump unit shall be suitable for use in Class I, Division 1, Group D locations as defined by the National Electrical Code.
The pump units shall be of the type easily removable and reinsertable, without entering the wetwell, by the use of a guide rail system. The guide rail system shall be of stainless steel, mounted in place from the bottom of the wetwell to a point close to the access hatch. A bracket on the pump unit shall mate with the guide rail. The pump discharge flange shall fit to the discharge pipe by means of a quick-disconnect sealing type flange.
A portable hoist of adequate capacity which can be inserted in a socket embedded or anchored in the top slab of the wetwell shall be provided to remove the pumps for inspection or servicing. A truck-mounted crane also may be used to lift the pumps out of the wetwell. Adequate space for this operation shall be provided near the wetwell. Ventilation equipment shall be so located as not to obstruct this operation.
Acceptable submersible nonclog pump manufacturers: Fairbanks Morse, Flygt, Hydromatic, and KSB.
Acceptable submersible grinder pump manufacturers: F.E. Meyers, Flygt, Goulds, and Hydromatic. (Design Guideline DG-08 § 5.7.)