Shaft deflection

Shafts. Shafts shall he suitable for hook-type sleeve. Shaft material shall he (SAE 1045 steel on Duron and 316 stainless steel pumps) or (AISI 316 stainless steel on CD-4MCu pumps and 20 stainless steel pumps). Shaft deflection shall not exceed. 005 at the vertical centerline of the impeller. 

Straight-Lobe Type This type is illustrated in Fig. 10-79. Such units are available for pressure differentials up to about 83 kPa (12 Ibf/in ) and capacities up to 2.549 X lO mvh (15,000 ftVmin). Sometimes multipfe units are operated in series to produce higher pressures individual-stage pressure differentials are limited by the shaft deflection, which must necessarily be kept small to maintain rotor and casing clearance. 

Note The shaft deflection should not be more lhan 11% of the air gap between the stator and the rotor. For loads that exert more force and torsional stress on the motor shaft and bearings than is permissible, due to the larger width of pulleys which may shift the... 

Sometimes, as a result of an unbalanced magnetic field, causing an air gap eccentricity or excessive shaft deflection, the motor is not able to maintain the small air gap between the rotor and the stator and this may lead to failure. 

Fig. 28.8. Exaggerated drawing of the deflections that occur in the loaded drum. The shaft deflects under four-point loading. This in turn causes the end plates to deflect out of plane, creating tensile (-r) and compressive (-) stresses in the weld.

The other ease is when there is too niiieh flow through the pump. The pump is operating to the right of the BEP on its eurve (Figure 9-8). The same problem oceurs, but now in the other direction. With the severe increase in velocity through the pump, the pressures tall dramatically in the H-F-G-H arc of the volute circle (Bernoulli s Law-says that as velocity goes up, pressure comes down). Now the shaft deflects, or even breaks in the opposite direction. .. at approximately 240° around the volute from the cutwater. 

Shaft deflection is the result of an external radial load. The external radial loading originates with the pump operator or proee.ss when the pump runs away from its best effieieney point on the curve. The resistance to deflection is a function of the shaft s overhang length and its diameter. The deflection resi.stanee, also called the flexibility laetor, is known as the L/D laetor. 

If you suspect, or know, that you have a deflected shaft, or know that standard operating procedure in your plant requires controlling the flow in the pipes by opening and closing valves, then you have three options to reduce shaft deflection ... 

An intensive radial load is created when operating near the shut-off head and the shaft deflects at about 60° from the cut-water. This concept is explained in Chapter 9 Shaft Deflection . The pump will be noisy, will vibrate and maintenance on seals, bearings and shaft sleeves is expected. 

The previous equation shows that when lu < uj ,8r is positive. Thus, when operating below the critical speed, the system rotates with the center of mass on the outside of the geometric center. Operating above the critical speed (lu > LUn), the shaft deflection 8r tends to infinity. Actually, this vibration is damped by outside forces. For very high speeds (lu >> LUn), the amplitude 8r equals —e, meaning that the disc rotates about its center of gravity. 

Nf. = critical speed, rpm < = siatic shaft deflection L, = L ravitational constant... 

Critical speed the mixer shaft speed which matches the first lateral natural frequency of the shaft and impeller system. Excessive vibrations and shaft deflections are present at this speed. 

Steady Bearing a bearing located at the bottom of the shaft of a top entering impeller to minimize shaft deflection and vibration. It is immersed in the fluid being mixed. 

The mixer manufacturer should always be consulted for proper mechanical features design and strength characteristics, such as horsepower, gear rating AGA, shaft diameter, shaft deflection, critical speeds, bottom steady bearing, and side shaft bearings. 

Rotational speed of shaft and peripheral speeds of seal. Mechanical limitations—dimensions of space required versus space available, shaft deflection and whip, shaft end play, shaft diameter, and maintenance. Miscellaneous factors—cost, allowable by-pass or out-leakage, allowable contamination of gas with air, inert gas, oil, and other fluid. 

The overhung design of the rotor (i.e., no outboard bearing) increases the potential for radical shaft deflection. Any variation in laminar flow, volume, or load of the... 

Most turbines have relatively long bearing spans and highly flexible shafts. These factors, coupled with variations in process flow conditions, make turbine rotors highly susceptible to shaft deflection during normal operation. Typically, turbines operate in either the second or third mode and should have narrowbands at the second (2x) and third (3x) harmonics of shaft speed to monitor for mode shape. 

The following parameters are monitored in a typical predictive-maintenance program for fans aerodynamic instability, running speeds, and shaft mode shape, or shaft deflection. 

A narrowband window should be established to monitor the fundamental (lx), second (2x), and third (3x) harmonic of shaft speed. With these windows, the energy associated with shaft deflection, or mode shape, can be monitored. 

A second radial (Y-axis) measurement point should be positioned at 90° to the primary in a plane that captures secondary shaft deflection. For the pump illustrated in Figure 44.21, the secondary (Y-axis) radial measurement point is located on top of the pump s bearing cap and oriented downward. Since the pump has a clockwise rotation, back-pressure in the discharge piping forces the shaft both downward and horizontally toward the front of the picture. 

A clear understanding of the mode shape, or shaft deflection, of a machine s rotating element is a valuable diagnostic tool. Both broadband and narrowband filtered energy windows can be used at each measurement point and orientation across the machine. The resultant plots, one in the vertical plane and one in the horizontal plane, provide an approximation of the mode shape of the complete machine and its rotating element. 

The Spencer blower in this example provides air to a drying process in a metal-coating line. Its configuration includes an end-suction inlet that is in-line with the shaft and a horizontal discharge that is perpendicular to the shaft. In this particular example, the source of the shaft deflection observed in the mode plot is aerodynamic instability. 

The problem is eliminated by restricting the discharge air flow from the blowers. By increasing the backpressure, the blowers are able to operate within their normal envelope and the shaft deflection disappears. 

Figure 44.32 Horizontal narrowband (lx) mode shape indicates shaft deflection...

Lubrication pressure feed critically important, required flow is large, susceptible to damage by contaminants and interrupted lubricant flow Quiet operation Moderate tolerance of shaft deflection... 

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