Maintenance-free pulse jet mixers (PJMs) consisting of a jet pump pair (JPP), gas ballast, and mixing nozzle are applicable for mixing hazardous liquid-solid mixtures that are radioactive, corrosive, and/or toxic. Currently, two problems need to be resolved to realize the potential application of PJMs in hazardous environments. The first problem is the detection of the maximum and minimum fluid levels in the gas ballast, which is independent of any electric components and/or mechanical moving parts directly in contact with a hazardous fluid. The second is how to inhibit the leakage of compressed air during the compression phases of the gas ballast. A novel method for detecting the maximum and minimum fluid levels in the gas ballast was proposed based on the Venturi principle and the sharp variation in the differential pressure signal, respectively. To inhibit the leakage of compressed air, a vortex diode was combined with the JPP, which was proven to be effective. A completely maintenance-free PJM was used to investigate the mixing performance in a water-glycerine-quartz sand mixture. The experimental results showed that the mixing performance improved with increases in the static pressure of the compressed air and the compression time, but decreased with increases in the liquid viscosity and fluid level in the storage tank. (C) 2012 Elsevier B.V. All rights reserved.