Rotary positive pumps

A homogenizer or rotary positive pump may be used as a timing or metering pump to provide a positive, fixed flow through the pasteurization system (Fig. 6). The pump is placed ahead of the heater and the holding section. Various control drives assure that the pasteurized side of the heat exchanger is at a higher (7 kPa (1 psi)) pressure than the opposite side. 

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. 

Rotary Positive Pump data sheet Equipment No. (Tag) Descript. (Func.) Sheet No. ... 

No priming is required with rotary positive pumps, and they are well adapted for pumping highly viscous fluids. A constant rate of delivery is obtained, and the fluid may be delivered at high pressures. Because of the small clearance that must be maintained, this type of pump should not be used with nonlubricating fluids or with fluids containing solid particles. 

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... 

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

This gives a target value to the pump supplier that is worst condition. In general, for cold water duty equation (32.16) can be used for the duty flow required. Equation (32.16) is employed for reciprocating and rotary positive displacement machines with allowance made for acceleration effects. 

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. 

Installation requirements for rotary positive-displacement compressors are similar to any rotating machine. Review the installation requirements for centrifugal pumps and compressors for foundation, pressure-relief, and other requirements. As with centrifugal compressors, rotary positive-displacement compressors must be fitted with pressure-relief devices to limit the discharge or inter-stage pressures to a safe maximum for the equipment served. 

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. 

The lowest pressure which can be achieved in a vacuum vessel. The so-called ultimate pressure Pgi j depends not only on the pump s suction speed but also upon the vapor pressure p j for the lubricants, sealants and propellants used in the pump. If a container is evacuated simply with an oil-sealed rotary (positive displacement) vacuum pump, then the ultimate pressure which can be attained will be determined primarily by the vapor pressure of the pump oil being used and, depending on the cleanliness of the vessel, also on the vapors released from the vessel walls and, of course, on the leak tightness of the vacuum vessel itself. 

Fig. 2.10 Operating cycie of a rotary piunger pump (for positions 1 to 9 of the plunger)...

A Roots vacuum pump (see Fig. 2.17) Is a rotary positive-displacement type of pump where two symmetrically-shaped Impellers rotate Inside the pump casing past each other In close proximity. The two rotors have a aoss... 

Vacuum is provided by a continuously running two-stage rotary vacuum pump (P). A three-way valve M) connects the bell jar either to the vacuum line or to the pressure line. Inserted into the vacuum line is a valve (N) which has a permanent bypass consisting of a coil of long, narrow steel tubing. In order to prevent the liquid in the cup from boiling, caused by too sudden fall in pressure, the system is evacuated first through the bypass with valve (IV) in the closed position. This valve is opened after a predetermined delay period. 

Process pumps are three types centrifugal, rotary positive displacement, and reciprocating. The outputs of all of them are controllable by regulation of the speed of the driver. 

Figure 5.6. Components of pneumatic conveying systems, (a) Rotary positive displacement blower for pressure or vacuum, (b) A rotary airlock feeder for fine materials (Detroit Stoker Co.), (c) A four-compartment receiver-filter (Fuller Co., Bethlehem, PA), (d) A two-stage cyclone receiver, (e) The Fuller-Kinyon pump for cement and other fine powders. Powder is fed into the aeration chamber with a screw and is fluidized with compressed air (Fuller Co., Bethlehem, PA).

On balance, centrifugal pumps always should be considered first in comparison with reciprocating or rotary positive displacement types, but those do have their places. Range of applications of various kinds of pumps are identified by Figure 7.14. 

Figure 7.19. Some rotary positive displacement compressors, (a) A two-lobe blower, (b) Performance of a two-lobe blower (Rools-Connersville Co.), (c) A screw pump with one power and two idle rotors (Kristal and Annett, 1940). (d) Performance of 3.5" screw pump handling oils at 1150 rpm against 325 psig (Kristal and Annett, 1940). (e) Principle of the liquid ring seal compressor (Nash Engineering Co.). (0 A sliding vane blower (Beaeh-Russ Co.).

Rotary positive-displacement pumps with no valve action gear pumps, lobe pumps, screw pumps, eccentric-cam pumps, metering pumps... 

Type of power supply. Rotary positive-displacement pumps and centrifugal pumps are readily adaptable for use with electric-motor or intemal-combus-tion-engine drives reciprocating pumps can be used with steam or gas drives. 

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