If you are a Commercial Plumbing Contractor you probably know that building redundancy into your mechanical systems is a good thing. In fact in many states the building codes requires a duplex pumping system for wastewater pump systems.
Some states, like Wisconsin, go as far as specifically requiring a pump and basin sizing formula. This formula essentially insures that the proper size equipment is used in order to meet the demand of the inflow based on the water that supplies the plumbing fixtures.
The SSPMA (Sump & Sewage Pump Manufacturing Association) also has a set of standards or “best practices” that guide the Plumber and Plumbing Designer on what will work too. In many cases the individual state codes have incorporated the SSPMA’s tried and true methods into their plumbing requirements.
The link below will get you to the SSPMA sizing guide lines power point and will fill you in on general pump system sizing terminology and methods.
As far as Wisconsin plumbing codes goes, the Pro’s at Jim Murray, Inc. actually have a State of Wisconsin DSPS continuing education class where both simplex and duplex sizing is covered.
The Pro’s at Jim Murray, Inc. can also help you reverse engineer a pump system in the event that and existing pump data or information due to age is not available.