Impellers or wheels

The general operation of a centrifugal compressor is like a centrifugal pump, except that the fluid is compressible. Theoretically, the head developed by a centrifugal impeller or wheel is the same regardless of the characteristics of the... 

P[3 = P[ = fan input power D = fan size (impeller or wheel diameter) N = fan speed Nj = fan specific speed p = fan air density Q = fan flow rate Kp = compressibility coefficient L, = sound power level Pjt = fan total pressure Pjy = fan velocity pressure Pj-s = fan static pressure... 

By considering the flow as stopped but the turbine casing full of liquid, it is intuitively obvious that to rotate the wheel or impeller in either direction power will have to be put in. As the flow increases... 

An expander-eompressor unit must be meehanieally tested and all meehanieal tests should be witnessed by the owner-purehaser or his representative. If the manufaeturer does not have the eapability of testing with the fully bladed eontraet rotor, a dummy wheel may replaee the eompressor impeller. This dummy wheel is a disk with no blades, designed to duplieate the weight, eenter of gravity, and moment of inertia of the aetual eompressor wheel. 

The maximum speed of a compressor is fixed by mechanical or structural limiting of the peripheral velocity of the impeller wheels. The required velocity is established by the head to be developed. The capacity of the machine at suction conditions is a function of the individual wheel designs and the diameter. ... 

At any constant or steady speed of operation of a compressor, the head-capacity and efficiency curves are characteristic of the impeller and casing design only. These curves that are determined by test can be translated to other reasonable speeds and conditions of operation of the wheel-casing combination of the affinity laws. The operation of the compressor must meet or establish the desired point on the head-capacity-system curve, which requires a combination of controls. 

Figure 12-121. Single-width wheel (or impeller) with forward curved blades. (Used by permission The Howden Fan Company.)...

Figure 12-151. Large size 8E blower performance chart, running at 3,570 rpm, up to 32 in. dia. wheel (or impeller), producing static pressure = 90 in. WG at 6,000 cfm, and higher cfm at lower sp. (Used by permission Bui. FI-411C, 1988. The Howden Fan Co.)...

Parts or process plant machines marine main-turhine gears centrifuge drums fans assembled aircraft gas-turbine rotors fly wheels pump impellers machine-tool and general machinery parts electrical armatures. 

Gear Pumps When two or more impellers are used in a rotary-pump casing, the impellers will take the form of toothed-gear wheels as in Fig. 10-54, of helical gears, or of lobed cams. In each case, these impellers rotate with extremely small clearance between them and between the surfaces of the impellers and the casing. In Fig. 10-54, the two toothed impellers rotate as indicated by the arrows the suction connection is at the bottom. The pumped liquid flows into the... 

Blasting. Using this procedure, scale is removed by high-velocity particles impelled by an air blast or by a high-velocity wheel. Blast materials usually consist of sand, or sometimes of steel grit, silicon carbide, alumina, refractory slag,... 

Rotary positive displacement pumps. These have two or more impellers in the form of toothed gear wheels or lobed cams which rotate with an extremely small clearance between each other and the pump casing. They have to be primed and they produce a pulsed output. 

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