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FIGURE 11 Positive displacement pump with constant discharge head

FIGURE 10 Comparison of adjustable-speed and constant-speed pressure and power characteristics for a typical centrifugal boiler-feed pump

FIGURE 11 Positive displacement pump with constant discharge head

-FIGURE 12 Thirteen fluid drives driving reciprocating pumps on a coal pipeline. The fluid drive absorbs a large percentage of the pulsations created by the reciprocating pumps and controls their speed to provide proper pipeline flow (American Davidson).

reservoir. Some special marine couplings utilize quick-dumping valves, but these are seldom, if ever, used with pump drives.

Obviously the speed at which the scoop tube is moved is also significant. Large polar moments of inertia (WK2 values) of the driven equipment will increase response time.

The scoop-trimming coupling offers the best overall response characteristics of the hydrokinetic drives, and standard catalog machines have normal fill times ranging from 10 to 15 s. They will accomplish 90% of a 10% step speed change in the 40 to 100% speed

FIGURE 13 Cutaway view of vertical fluid drive suitable for operation with vertical pumps. Note the NEMA P pump flange and output shaft (American Davidson)

FIGURE 14 Fluid drive of Figure 13 mounted on a vertical-shaft pump (American Davidson)

FIGURE 13 Cutaway view of vertical fluid drive suitable for operation with vertical pumps. Note the NEMA P pump flange and output shaft (American Davidson)

FIGURE 14 Fluid drive of Figure 13 mounted on a vertical-shaft pump (American Davidson)

range in 7 to 20 s if coupled to a "normal load inertia." Special units are in operation where this change is accomplished in 2 to 6 s.

Hydrodynamic and Hydroviscous Drive Both hydrodynamic and hydroviscous couplings respond very quickly to a change in demand for torque output. Both require a mechanical motion (change in valve position or change in spacing between disks) followed immediately by a change in pressure or in film thickness.

In most cases, the torque available for speed change and the WK2 values involved are of such a magnitude that the major portion of the response time is caused by inertial effects rather than by the time required to change torque. This is particularly true in the deceleration of centrifugal pumps. Unless auxiliary brakes are built-in, none of the hydro-kinetic, hydrodynamic, or hydroviscous drives can provide dynamic braking. On a demand to decrease speed, they can at best reduce driving torque to zero. Under these circumstances, the only retarding force to slow the inertia of the driven machine is the load it developed. In the case of centrifugal pumps on fixed systems, this load would fall off as the cube of speed, and below 40% of full speed, such pumps have an almost insignificant braking effect.

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Survival Treasure

This is a collection of 3 guides all about survival. Within this collection you find the following titles: Outdoor Survival Skills, Survival Basics and The Wilderness Survival Guide.

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