Reliability Analytics Corporation
Previous | Next      Search Home

First 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 Last

First 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 Last

Previous | Next      Search Home

10.7 FAILURE RATE MODEL FOR PUMP CASING, XCA The pump casing is normally a very reliable component. Defined as kCA, the casing failure rate will have a greater effect on total pump reliability from the standpoint of how it affects other less reliable components. For instance, for an ANSI pump, the casing may have an average life expectancy of 10 years where a seal or bearing may have only one or two years. However, the type of casing used in the pump can have a large effect on the lifetime of the bearings and seals. This is due to differing loads placed on the pump shaft by the fluid flow pattern. The fluid flow patterns are a function of the casing design. The failure rate of the pump casing (ACa) itself can be estimated at 0.01 failures/million hours. 10.8 FAILURE RATE MODEL FOR FLUID DRIVER, AFD All pumps require some vehicle to move the fluid from the intakes and expel it through the volutes and output ports to the exhaust opening. The means by which pumps do this is what differentiates most of today's numerous types of pumps. The reliability of these fluid drivers will vary from pump to pump. Impellers will wear out long after the seals. Pump gears for rotary gear pumps will have a lower reliability than impellers due to the nature of the contact between gears and the speed they attain. Piston-plunger displacement pumps will generally have greater wear rates for the piston walls and rings than for the impellers of centrifugal pumps. The average failure rates in Table 10-4 have been determined from data base information developed from various failure rate data sources. The equations that describe the fluid driver wear rate may vary drastically since the fluid driver varies greatly in design and application. Other chapters of this Handbook can be used to estimate the failure rates for slider-crank mechanisms, mechanical couplings, valves and other components and parts unique to the particular pump design. In a centrifugal pump, the net positive suction head (NPSH) varies as a function of flow determined by pressure. In a positive displacement pump NPSH varies as a function of flow determined by speed. Reducing the speed of a positive displacement pump reduces the NPSH. NPSHA is the actual NPSH and NPSHR is the required NPSH obtained from the pump manufacturer. Depending on the pump design a NPSHA / NPSHR margin of 1.1 to 2.5 should be obtained. The failure rate of a pump fluid driver can be estimated from the following equation: kFD - kFD B CPF CPS Cc CSF (10-3) Pumps 10-10 Revision C

Toolkit Home

Reliability Analytics Corporation
reliabilityanalytics.com