When should the transfer valve be switched to Volume (parallel)?

• A. When you expect to pump more than 50% of the pump's rated capacity
• B. When you are pumping less than 10% of capacity
• C. When you are drafting from a static source
• D. When you are using foam proportioning

Answer: (A)

Switching to Volume (parallel) is about maximizing flow. In a two-stage pump, the transfer valve controls whether the two pump stages operate in series to boost pressure or in parallel to increase overall flow. When you set it to Volume (parallel), both stages contribute to the same discharge, raising the total gallons per minute you can deliver. This mode is most effective when your anticipated demand is substantial—roughly more than half of the pump’s rated capacity—because the gain in flow from using both stages outweighs the drop in pressure. If you expect only modest flow, staying in the pressure/series mode preserves higher pressure with fewer pumps contributing, which is appropriate for long or smaller-diameter lines. Drafting from a static source or using foam proportioning doesn’t by itself mandate a switch; those scenarios relate more to supply stability or nozzle/foam system requirements, whereas volume mode specifically addresses higher flow needs.