Pneumatic pulse jet pumps are air-powered, low-maintenance devices useful for delivering hazardous liquids. A key component in these pumps is the reverse-flow diverter (RFD), consisting of a nozzle and a diffuser. Despite several decades of practical application, no clear guidelines exist for RFD design during the reverse-flow portion of the pumping cycle. We experimentally investigated the effects of diffuser entrance/nozzle exit area ratio, suction gap length, and diffuser divergence angle on RFD flow and pressure. The results were used to derive two dimensionless performance coefficients (zeta(M) = 0.50(phi)(0.38) and q = A + B . exp[-Eu-out/(C . Eu-0)] + D . exp[-Eu-out/(E . Eu-0)]) and to develop a series of design guidelines for RFDs in reverse-flow mode.