Priming event peak pressures in liquid propulsion systems

An experimental study was conducted to evaluate pressure transient levels in unrestricted and restricted liquid monopropellant propulsion system configurations and propellant manifolds generated by water hammer effects resulting from a priming event. This was accomplished through the development of a priming event experimental setup using distilled water as a propellant simulant for hydrazine. Multiple test elements were evaluated using different internal diameters, line lengths, manifold layouts, and flow control valves at atmospheric, subatmospheric, and low-pressure pretest pressure levels. The goals of the research were to determine the influence of restrictions in a liquid propulsion system, as well as the propellant manifold design, in the mitigation of the priming event maximum pressure levels. Based upon experimental results, it was determined that the internal diameter, line length, valve flow coefficient, and pretest pressure level all contributed to the pressure magnitude of the priming event. It was also observed that peak water hammer pressure levels might be significantly minimized and equally distributed throughout a propulsion system manifold using an inline cavitating venturi and manifold layout promoting free flow of the fluid, which was independent of the line geometry, the valve flow coefficient, and the valve opening response time.