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  1. vanstoja

    Pump Shaft Failure Possibility

    For an extensive discussion of the estimation of minimun operating flows for centrifugal pumps see vanstoja and others' replies in Thread407-104691.
  2. vanstoja

    Removal of Impeller

    You shouldn't remove either impeller stage if you can avoid it because you may be faced with difficult shaft radial or axial loading and rotordynamics rebalancing problems. The first stage is more important because it is usually designed to meet the cavitation design needs whereas the 2nd stage...
  3. vanstoja

    Cooling tower Fan failures

    For airfoil blades of this huge diameter the blade support system appears to be about as flimsy as I have ever seen and presuming that bolts are holding down the two U-shaped brackets for each blade, it is no wonder that they might easily be overstressed by even ideal flow conditions over the...
  4. vanstoja

    Centifugal pump with water and air

    With a suction pressure of 120 psig and a pump head of about 86.6 psi(200 ft.) giving a discharge pressure of 206.6 psig you would need a guillotine pipe break in either the suction or discharge piping to allow any significant entry of ambient air to the piping system. If a guillotine break...
  5. vanstoja

    Pump Minimum Flow - mechanical protection

    Recirculation flow in a centrifugal pump inlet at off-design (particularly low) flowrates is akin to stall on an airplane wing when the flow incidence angle becomes too high. Most airfoil shapes stall with incidence angles of about 12 to 18 degrees. Heatup cavitation effects are only likely when...
  6. vanstoja

    Inlet and outlet of Meridional Velocity on radial impeller design

    Beta 2 and b2 are actually independent variables in the iterative design process employing Stepanoff's method. The example I cited calculated design parameters for 7 impeller blades with b2 in 0.2 inch increments from 1.8 to 2.4 inches and Beta 2 in 1 degree increments from 18 to 23 degrees...
  7. vanstoja

    Inlet and outlet of Meridional Velocity on radial impeller design

    The two books you cite are probably referring to different methods of design which may be individually consistent but not comparable for specific design parameters. The method employing suction and discharge capacity constants Km1 and Km2 is the specific speed impeller design approach originally...
  8. vanstoja

    Air Cooled vs Water Cooled

    Water cooled motors are either of the "wet-winding" or "canned" design configuration both of which are designed to withstand the water environment with the former type probably more likely to be employed for power ratings in the megawatt range. Canned motor designs are generally limited to...
  9. vanstoja

    Radial flow and Mix flow diffuser vane layout design

    The books by the three authors you mention probably provide the best "layout" treatment of impeller and diffuser blade/vane design among the pump design books published since the 1950's. Lazarkiewicz and Troskolanski's book may be in this same class. Recent blade/vane design procedures used in...
  10. vanstoja

    SPEED LIMITATIONS BY VFD

    The cubed increase in motor power with rotating speed cited by hydrae also applies (nearly) to motor current assuming a constant power factor. Since heat input to the motor winding varies as I^2*R where I is current and R is winding resistance, doubling of speed causes winding conductor heat...
  11. vanstoja

    rotodynamics books: anyone knows some of these?

    For a more comprehensive list of rotrodynamics textbooks see www.xlrotor.com/booklist.htm by Brian Murphy which lists sources of available books. The Tondl book #4 is listed there and I reviewed it many years ago. It is not a basic text by any stretch. Tondl is probably the world's best...
  12. vanstoja

    Minimum straight length requirements before suction nozzle

    For further discussions of of the criticality of centrifugal pump and adjacent component suction and discharge pipe spacing see vanstoja and others replies in the following related threads: thread407-106384 thread378-78272 thread407-129352 thread378-109206
  13. vanstoja

    Pumps sealing

    Impeller flow leakage around the outside of the impeller represents a loss that degrades pump hydraulic efficiency and possibly head. Impeller seals near the impeller OD in axial leakage flow passages are usually of the plain annular or labyrinth teeth configuration. Inboard, at the impeller...
  14. vanstoja

    Shut off Pressure / Design Pressure Ratio

    Steepness of centrifugal pump head-flow curves generally depends on pump specific speed with axial flow pumps of high specific speeds having the steepest curves and the highest shutoff to design flow head ratios which might approach or even exceed 2.0. See Stepanoff's plots for various head-flow...
  15. vanstoja

    NPSH Curve

    jjpellin's description is generally correct for a closed, pressurized system NPSH test described in the Hydraulic Institute Standard or ASME Power Test Code, but "pinching down on the pump suction" is a rather vague term for the process of stepwise reduction in suction pressure to the pump. When...
  16. vanstoja

    Axial Load

    Axial hydraulic thrust measurements in centrifugal pumps with rolling element bearing motors have been made with axial load cells and sometimes strain gaged beam structures installed in direct contact with the rolling element bearings. This requires special modifications to motor end caps to...
  17. vanstoja

    Pump Vibration Range

    The most recent Hydraulics Institute Standard I have seen gives for vertical pumps with piggyback mounted motors of 5 feet or less height at 710 RPM a displacement limit of 5 mils peak-to-peak at the top motor bearing (Fig.77). For vertical non-clog pumps the limit is about 8 mils p-p at 710 RPM...
  18. vanstoja

    Non-seal Pump

    In canned motor pumps rated up to 1000 horsepower, conventional circuit breakers are employed for protection against locked rotor and current overload conditions. Locked rotor trip protection is usually based on rotor bar temperature rise time limits which may be of the order of ten seconds or...
  19. vanstoja

    Ball Bearing Stiffness (horizontal and vertical)

    Because of the geometric symmetry of ball bearings, I would expect the quadrature stiffness (perpendicular to load and axial directions) to be about the same as the load direction stiffness. The maximum difference should be equal to the loading in the load direction and may be influenced by the...
  20. vanstoja

    Run-out condition

    To achieve best efficiency conditions, a centrifugal pump should normally be operated within a range of about plus or minus 15% of rated (design point) flow. Beyond that range, impeller inlet flow incidence angles generally become too great for smooth, undistorted flow through the impeller...

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