Horizontal liquid reducers are always eccentric, top flat (unless on control set, same as PV, TV, HV, LV) or (pipe rack), which prevents the build up of air bubbles in the system. Eccentric reducers are used at the suction side of pumps to ensure air does not accumulate in the pipe. The gradual accumulation of air in a concentric reducer could result in a large bubble that could eventually cause the pump to stall or cause cavitation when drawn into the pump.