Centrifugal pump casing

Volume 1 explains that pumps ean be classified as either positive-displacement or kinetie. The same is true for compressors. In a positive displacement compressor the gas is transported from low pressure to high pressure in a device that reduces its volume and thus inereases its pressure. The most common type of positive displacement eompressors are reeiprocating and rotary (serew or vane) just as was the ease for pumps. Kinetic compressors impart a veloeity head to the gas, which is then converted to a pressure head in accordance with Bernoulli s Law as the gas is slowed down to the velocity in the discharge line. Just as was the case with pumps, centrifugal compressors are the only form of kinetic compressor commonly used. 

Erosion corrosion of pump impellers, casings and wear plates can be very troublesome. Positive-displacement pumps create much less turbulence than centrifugal or axial-flow pumps and should be used where possible in critical... 

All types of equipment, exposed to fluids in motion, are subject to the erosion-corrosion phenomena. This can include pipeline networks (particularly curves, elbows and T-squares), floodgates, pumps, centrifugal fans, helixes, wheels of turbine, tubes of intersections of heat exchangers and measuring devices. In many cases, failures due to erosion-corrosion occur in a relatively short time.16 Most metals are susceptible to erosion-corrosion in the liquid phase under specific conditions. Resistance of metals depends on the physical and chemical properties of the corrosion product and/or the... 

As in the case of pumps, centrifugal (and for lower heads with higher... 

I have read that pump cavitation is typically accompanied by the sound of nuts and bolts ratcheting around in a metal bucket. Much of the time this is not true. I typically cannot identify a large centrifugal pump in hydrocarbon service that is cavitating by the sound of the pump. If the pump discharge pressure is erratically low, this is a more reliable indication of cavitation than sounds omitted from the pump s case. Erratically low motor driver amperage also indicates pump cavitation. 

A centrifugal pump, in its simplest form, consists of an impeller rotating within a casing. The impeller consists of a number of blades,... 

The fuel. skid. This could contain a gas compressor if the fuel gas pressure is low and a knockout drum for any liquid contamination that the gas may have. The requirement of fuel gas pressure is that it should be operated at a minimum of 50-70 psi (3.5-4.83 Bar) above the compressor discharge pressure. The compressor and its motor drive fall under the drive level hierarchy. In the case of liquid fuels, the skid may also contain a fuel treatment plant, which would have centrifuges, electrostatic precipitators, fuel additive pumps, and other equipment. These could be directly controlled by the D-CS system, which would then report its readiness to the gas turbine controller. 

If still greater force is required, a positive pressure in excess of atmospheric can be applied to the suspension by a pump. This motive force may be in the form of compressed air introduced in a montejus, or the suspension may be directly forced through a pump acting against the filter medium (as in the case of a filter press), or centrifugal force may be used to drive the suspension through a filter medium as is done in screen centrifuges. 

If the suspension is fed to the filter with a reciprocating pump at constant capacity, filtration is performed under constant flowrate. In this case, the pressure differential increases due to an increase in the cake resistance. If the suspension is fed by a centrifugal pump, its capacity decreases with an increase in cake resistance, and filtration is performed at variable pressure differentials and flowrates. 

Pump and Downstream Equipment - A PR valve is required for a pump when the shutoff pressure of the pump is greater than the design pressure of the discharge piping, downstream equipment, or pump casing. Positive displacement pumps normally require such protection, while in most cases centrifugal pumps do not. 

In the true gravity case, pumps are not used. If, however, the liquid is highly viscous, to achieve efficient operation, pumps are required to force the fluid through the pressure filters. The pump can be considered essentially as a press with a plate-and-frame filter. The plate-and-frame filter consists of a series ot frames over which the filter medium is stretched. A centrifugal basket of fine mesh is another method of particulate removal. 

Figure 3-6. Cross-section horizontal two-stage horizontal split case centrifugal pump. (Courtesy Ingersoll-Rand Co.)...

Figure 3-9. Vertical multistage centrifugal pump with barrel casing. (Courtesy Allis-Chalmers Mfg. Co.)...

Centrifugal pumps with diffusion vanes are called diffusion pumps or, more recently, vertical turbine pumps. Those pumps with volute casings are called volute pumps. 

Centrifugal pumps require a rigid foundation that prevents torsional or linear movement of the pump and its baseplate. In most cases, this type of pump is mounted on a concrete pad or pedestal having enough mass to securely support the baseplate, pump and its driver. The following general mles apply to foundation design. 

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