Impellers Enclosed

The Kennedy extractor (Fig. 18-87), also requiring little head-room, operates substantially as a percolator that moves the bed of solids through the solvent rather than the conventional opposite. It comprises a nearly horizontal line of chambers through each of which in succession the solids being leached are moved by a slow impeller enclosed in that section. There is an opportunity for drainage between stages when the impeller lifts sohds above the liquid level before dumping them into the next chamber. Solvent flows countercur-rently from chamber to chamber. Because the solids are subjected to mechanical action somewhat more intense than in other types of... 

Increase the diameter of the eve of enclosed impellers. This reduces Hi. 

With the pump di.sa.ssemblcd in the shop, with open impellers, the damage is seen on the leading edge of the impeller blades toward the eye of the impeller, and on the blade tips toward the impeller s OD. With enclosed impellers, the damage reveals itself on the wear bands between the impeller and the volute casing. See the illustration (Figure 3-2). 

This condition cannot be corrected on pumps with an enclosed impeller. You need to relax the restricted discharge flow on the pump. The problem could be a clogged downstream filter, a closed discharge valve, an over-pressurized header (back-pressurizing the pump), or a... 

Totally enclosed impellers are designed with the blades between two support shrouds or plates. These impellers are for totally clean liquids because tolerances are tight at the eye and the housing, and there is no room for suspended solids, crystals or sediment, see Figure 6-18. 

The scratch marks on the circumference of these close tolerance rotary parts will correspond to. scratch marks on close tolerance stationary parts at approximately 60 around the volute from the cutwater. These marks will be vi.sible on the back plate with open impellers, or on the wear rings of pumps with enclosed impellers, or the ID bore of the restriction bushing at the bottom of the seal chamber where the shaft pa.sses through, or the ID of the seal chamber bore at the back end of the mechanical seal (Figure 9-6 and Figure 9-7, next page). 

The wear hands on pumps with enclosed impellers. 

Linnecessary noise, these should be cleaned regularly. Imbalance, whether due to dirt or to other causes, should be corrected by adjustment. Detective bearings should be adjusted or replaced. Struts and sharp edges in front of an impeller should be avoided. Impact noise insulation should be introduced between fan room and floor structure and between fan room and connecting ducts. The fan unit should be enclosed, with satisfactory airborne sound insulation as the objective. 

Enclosed Type Impeller Hydraulically Balanced for Reduced Thrust Load... 

Figure 3-2. Cut-a-way section of single-stage pump. Part 1 (above) enclosed type impeller. Part 2 (lower left) open type impeller. (Courtesy Peerless Pump Div. FMC Corp.)...

Enclosed double-suction Impeller with sealing rings on both sides. (Courtesy The Deming Co.)... 

Semi-open or seml-enclosed impeller. (Courtesy Goulds Pumps Inc.)... 

Circulates by radially directed centrifugal force using enclosed impeller stators. Circulation very good. 

Power is the external measure of the mixer performance. The power put into the system must be absorbed through friction in viscous and turbulent shear stresses and dissipated as heat The power requirement of a system is a function of the impeller shape, size, speed of rotation, fluid density and viscosity, vessel dimensions and internal attachments, and posidon of the impeller in this enclosed system. 

Figure 12-46D, Part 1. View toward inlet of 4 Vj-in. diameter brazed aluminum impeller. Note Regardless of the metal of manufacture, enclosed impellers with back-leaning blades are extremely useful in applications requiring a steep head-volume characteristic and the highest attainable efficiency. Applications include parallel operation with other compressors or boosting of another compressor s output. The power-volume curve will show a self-limiting feature at higher volumes. This feature is very beneficial when the driver has limited power available but operation throughout the full capacity range is required. (Used by permission A C Compressor Corporation.)...

Impellers can be further classified with regard to their physical design a closed impeller has shrouds or sidewalls enclosing the fluid flow, an open impeller has no shrouds or sidewalls, and a semiopen impeller is a mix of the closed and open design. 

The pinion shafts are typically a cantilever-type design that has an enclosed impeller on one end and a tilting-pad bearing on the other. The pinion gear is between these two components. The number of impeller-pinions (i.e. stages) varies with the application and the original equipment vendor. However, all bullgear compressors contain multiple pinions that operate in series. 

IMPELLER, hydraulically balanced — double suction enclosed type for better performance under critical suction conditions. 

Unless otherwise approved by the purchaser, impellers shall be of the fully enclosed type and constructed as single piece castings. Fabricated impellers require the purchaser s specific approval. 

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