Rotary pumps displacement

The most widely used pumps in the oil and gas industry are reciprocating displacement pumps (in particular piston plunger type), the rotary displacement pump, and the centrifugal dynamic pump. Only these pumps will be discussed in detail. 

Operating chart, 385 Operating range, 386 Performance curve, 386 Rotary displacement pump, 397 Rotary lobe blowers, 390, 392, 394 Rotary lobe performance curves,... 

Kreiselpumpen und rotierende Verdrangerpumpen hermetischer Bauart (Hermetic pumps and rotary displacement pumps). 

While the difficulties encountered to date have been relatively minor mechanically, the presence of plutonium makes any equipment change difficult. The transfer and fast fuel addition pumps were originally gear pumps, but failure to self-prime led to their replacement by rotary displacement pumps. Tliese latter pumps have teen successful, ... 

Positive Pumps. Positive pumps employed by the food industry have a rotating cavity between two lobes, two gears that rotate in opposite directions, or a crescent or stationary cavity and a rotor. Rotary positive pumps operate at relatively low speed. Fluid enters the cavity by gravity flow or from a centrifugal pump. The positive pump also may use a reciprocating cavity, and may be a plunger or piston pump. These pumps are not truly positive with respect to displacement, but are used for metering product flow. 

Positive-displacement pumps may be of either the reciprocating or the rotary type. In all positive-displacement pumps, a cavity or cavities are alternately filled and emptied of the pumped fluid by the action of the pump. 

Rotary Pumps In rotary pumps the liquid is displaced by rotation of one or more members within a stationary housing. Because internal clearances, although minute, are a necessity in all but a few special types, capacity decreases somewhat with increasing pump differentia pressure. Therefore, these pumps are not truly positive-displacement pumps. However, for many other reasons they are considered as such. 

A strainer should be used in the pump suction line temporarily for a centrifugal pump and permanently for the rotary positive displacement pump. For the permanent installations, a Y-type strainer with an austenitic stainless strainer basket should be used. The cross-sectional... 

Other positive displacement pumps, such as rotary, gear, and diaphragm pumps, normally require PR valve protection for both the pump and downstream equipment. PR valves for all positive displacement pumps should have a capacity at least equal to the pump capacity. 

Pumps may be classified as reciprocating, rotary, or centrifugal. The first two are referred to as positive-displacement pumps because, unlike the centrifugal type, the liquid or semiliquid flow is broken into small portions as it passes through the pump. 

Figure 6-50. Typical rotary displacement vacuum pump, oil sealed, single-stage. By permission, Kinney Vacuum Co.

The reciprocating and rotary positive displacement pumps primary characteristic is that they have a nearly direct relationship between the motion of the pumping... 

If a centrifugal is not suitable, select a rotary positive displacement pump. The design usually selects itself. 

Performance of a rotary positive-displacement compressor can be evaluated using the same criteria as a positive-displacement pump. As constant-volume machines, performance is determined by rotation speed, internal slip, and total back-pressure on the compressor. 

Since changes in pump speed affect volumetric output, some pumps are rated by their displacement. Pump displacement is the amount of fluid the pump can deliver per cycle or complete rotation. Since most pumps use a rotary drive, displacement is usually expressed in terms of cubic inches per revolution. 

Positive-displacement pumps can be divided into two major types rotary and reciprocating. All rotary pumps use some form of rotating element, such as gears, vanes, or lobes to increase the discharge pressure. Reciprocating pumps use pistons or wobble plates to increase the pressure. 

Rotary Locations of measurement points for rotary positive-displacement pumps should be based on the same logic as in-line centrifugal pumps. The primary (X-axis) radial measurement should be taken in the plane opposite the discharge port. The secondary (Y-axis) radial should be at 90° to the primary and in the direction of the rotor s rotation. 

Since most rotary positive-displacement pumps have inlet and outlet ports in the same plane and opposed, there should be relatively little axial thmsting. However, an axial (Z-axis) measurement should be acquired from the fixed bearing, oriented toward the driver. 

Reciprocating and rotary positive displacement pumps are commonly used where moderately low vacuum is required, about 10 mmHg (0.013 bar), at moderate to high flow rates such as in vacuum filtration. 

A slurry is being filtered at a net rate of 10,000 gal/day by a plate and frame filter with 15 frames, with an active filtering area of 1.5 ft2 per frame, fed by a positive displacement pump. The pressure drop varies from 2 psi at start-up to 25 psi after 10 min, at which time it is shut down for cleanup. It takes 10 min to disassemble, clean out, and reassemble the filter. Your boss decides that it would be more economical to replace this filter with a rotary drum filter using the same filter medium. The rotary filter operates at a vacuum of 200 mmHg with 30% of its surface submerged and rotates at a rate of 5 min/rev. If the drum length is equal to its diameter, how big should it be ... 

For the most part, positive displacement pumps can be classified either as rotary pumps or as reciprocating pumps. However, pumps do exist which exhibit some of the characteristics of both types. 

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