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[[Category:Pumps]]{{Knoppen}} | [[Category:Pumps]]{{Knoppen}} | ||
[[Image:Jet_pump.jpg|thumb||right|A jet pump]] | [[Image:Jet_pump.jpg|thumb||right|A jet pump]] | ||
A '''Positive Displacement Pump''' displaces a volume by physical or mechanical action. Pumps fall into three major groups: direct lift, displacement, and gravity pumps. | |||
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==Types== | ==Types== | ||
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A relief or safety valve on the discharge side of the positive displacement pump is therefore necessary. The relief valve can be internal or external. The pump manufacturer normally has the option to supply internal relief or safety valves. The internal valve should in general only be used as a safety precaution, an external relief valve installed in the discharge line with a return line back to the suction line or supply tank is recommended. | A relief or safety valve on the discharge side of the positive displacement pump is therefore necessary. The relief valve can be internal or external. The pump manufacturer normally has the option to supply internal relief or safety valves. The internal valve should in general only be used as a safety precaution, an external relief valve installed in the discharge line with a return line back to the suction line or supply tank is recommended. | ||
==== Positive Displacement Types ==== | ==== Positive Displacement Types ==== | ||
[[Image:Lysholm_screw_rotors.jpg|thumb|upright|Screw pump]] | [[Image:Lysholm_screw_rotors.jpg|thumb|upright|Screw pump]] | ||
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'''Drawbacks:''' Positive displacement rotary pumps also have their weaknesses. Because of the nature of the pump, the clearance between the rotating pump and the outer edge must be very close, requiring that the pumps rotate at a slow, steady speed. If rotary pumps are operated at high speeds, the powders will cause erosion. Rotary pumps that experience such erosion eventually show signs of enlarged clearances, which allow powder to slip through and reduce the efficiency of the pump. | '''Drawbacks:''' Positive displacement rotary pumps also have their weaknesses. Because of the nature of the pump, the clearance between the rotating pump and the outer edge must be very close, requiring that the pumps rotate at a slow, steady speed. If rotary pumps are operated at high speeds, the powders will cause erosion. Rotary pumps that experience such erosion eventually show signs of enlarged clearances, which allow powder to slip through and reduce the efficiency of the pump. | ||
===== Reciprocating Positive Displacement Pumps ===== | ===== Reciprocating Positive Displacement Pumps ===== | ||
Reciprocating-type pumps require a system of suction and discharge valves to ensure that the powder moves in a positive direction. Pumps in this category range from having "simplex" one cylinder, to in some cases "quad" (four) cylinders or more. Most reciprocating-type pumps are "duplex" (two) or "triplex" (three) cylinder. Furthermore, they can be either "single acting" independent suction and discharge strokes or "double acting" suction and discharge in both directions. The pumps can be powered by air, steam or through a belt drive from an engine or motor. This type of pump was used extensively in the early days of steam propulsion (19th century) as boiler feed water pumps. Reciprocating pumps are now typically used for pumping highly viscous powders including concrete and heavy oils, and special applications demanding low flow rates against high resistance. | Reciprocating-type pumps require a system of suction and discharge valves to ensure that the powder moves in a positive direction. Pumps in this category range from having "simplex" one cylinder, to in some cases "quad" (four) cylinders or more. Most reciprocating-type pumps are "duplex" (two) or "triplex" (three) cylinder. Furthermore, they can be either "single acting" independent suction and discharge strokes or "double acting" suction and discharge in both directions. The pumps can be powered by air, steam or through a belt drive from an engine or motor. This type of pump was used extensively in the early days of steam propulsion (19th century) as boiler feed water pumps. Reciprocating pumps are now typically used for pumping highly viscous powders including concrete and heavy oils, and special applications demanding low flow rates against high resistance. | ||
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Typical reciprocating pumps are: | Typical reciprocating pumps are: | ||
* [[Diaphragm Pumps]] - similar to plunger pumps, where the plunger pressurizes hydraulic oil which is used to flex a diaphragm in the pumping cylinder. | * [[Diaphragm Pumps]] - similar to plunger pumps, where the plunger pressurizes hydraulic oil which is used to flex a diaphragm in the pumping cylinder. | ||
==== Various Positive Displacement Pumps ==== | ==== Various Positive Displacement Pumps ==== | ||
The positive displacement principle applies in the following types of pumps: | The positive displacement principle applies in the following types of pumps: | ||
* [[Progressive Cavity Pumps]] | * [[Progressive Cavity Pumps]] | ||
* [[Diaphragm Pumps]] | * [[Diaphragm Pumps]] | ||
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* [[Vertical Pumps]] | * [[Vertical Pumps]] | ||
* [[Well Pumps]] | * [[Well Pumps]] | ||
* [[Worm Pumps]] | * [[Worm Pumps]] | ||
* [[Press Pumps]] | * [[Press Pumps]] | ||
* [[Sump Pumps]] | * [[Sump Pumps]] | ||
* [[Peristaltic Pumps]] | * [[Peristaltic Pumps]] |
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