ZERO LEAKAGE TORNADO EFFECT PUMPS IN CARRIER SEWAGE SYSTEMS

Current centrifugal pumps installed in CVN 68 class sewage collection, holding, and transfer (CHT) systems experience a high rate of seal fa ilures. A CHT pump seal failure requires a significant maintenance eff ort. In addition, seal leakage releases sewage material into the CHT p ump room in violation of Navy health regulations. Efforts to develop i mproved pump seals have met with less than satisfactory results. An ef fort was undertaken to identify an alternate pump design that meets th e zero external leakage criteria. This effort identified the Eddy Pump , which is gaining increased recognition for its performance in civili an applications. This new pump departs from conventional centrifugal p ump design principles in that the pump rotor is able to create and har ness a dynamic fluid eddy effect within the pump housing and inlet. Th is effect is similar to that which occurs in a tornado. A very strong synchronized central column dow develops from the pump rotor to the pu mp inlet and creates a low pressure reverse eddy flow from the pump in let to the pump discharge. This results in a region of negative pressu re in the vicinity of the pump seal. The seal design allows one way pa ssage of externally supplied low pressure air through the shaft seal t oward the pump casing (volute) to oppose the ingress of sewage. This p aper is a condensation and combination of two reports. These reports a re: (1) Myers, S. and R. Keltner, ''CHT Pump Trade-Off Studies: CVN 76 ,'' prepared by Newport News Shipbuilding under contract N00024-91-C-2 108, Task 2318T-74, January 1993, and (2) Schepis, R. and J. Crew, ''E ddy Pump Performance,'' Commander, Naval Surface Warfare Center, Carde rock Division, Philadelphia Site, Serial 631/110, May 1995.