Difference between revisions of "Pumps"

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[[Image:Lysholm_screw_rotors.jpg|thumb|upright|Screw pump]]
[[Image:Lysholm_screw_rotors.jpg|thumb|upright|Screw pump]]
A '''pump''' displaces a volume by physical or mechanical action.  Pumps fall into three major groups: direct lift, displacement, and gravity pumps.
A '''pump''' displaces a volume by physical or mechanical action.  Pumps fall into three major groups: direct lift, displacement, and gravity pumps.
==Types==
==Types==
===[[Positive Displacement Pumps]]===
===[[Positive Displacement Pumps]]===
A positive displacement pump causes a powder to move by trapping a fixed amount of it and then forcing (displacing) that trapped volume into the discharge pipe.
A positive displacement pump causes a powder to move by trapping a fixed amount of it and then forcing (displacing) that trapped volume into the discharge pipe.


Some positive displacement pumps work    using an expanding cavity on the suction side and a decreasing cavity  on  the discharge side. powder flows into the pump as the cavity on the    suction side expands and the powder flows out of the discharge as the    cavity collapses. The volume is constant given each cycle of  operation.
Some positive displacement pumps work    using an expanding cavity on the suction side and a decreasing cavity  on  the discharge side. powder flows into the pump as the cavity on the    suction side expands and the powder flows out of the discharge as the    cavity collapses. The volume is constant given each cycle of  operation.
==== Positive Displacement Pump behavior and safety ====
==== Positive Displacement Pump behavior and safety ====
Positive    displacement pumps, unlike centrifugal or roto-dynamic pumps, will in    theory produce the same flow at a given speed (RPM) no matter what  the  discharge pressure. Thus, positive displacement pumps are constant  flow  machines. However due to a slight increase in internal leakage  as the  pressure increases, a truly constant flow rate cannot be  achieved.
Positive    displacement pumps, unlike centrifugal or roto-dynamic pumps, will in    theory produce the same flow at a given speed (RPM) no matter what  the  discharge pressure. Thus, positive displacement pumps are constant  flow  machines. However due to a slight increase in internal leakage  as the  pressure increases, a truly constant flow rate cannot be  achieved.
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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 ====
A positive displacement pump can be further classified according to the mechanism used to move the powder:
A positive displacement pump can be further classified according to the mechanism used to move the powder:
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* '''Rotary-type''' positive displacement: internal gear, screw, shuttle block, flexible vane or sliding vane, circumferential piston, helical twisted roots (e.g. the Wendelkolben pump) or powder ring vacuum pumps.
* '''Rotary-type''' positive displacement: internal gear, screw, shuttle block, flexible vane or sliding vane, circumferential piston, helical twisted roots (e.g. the Wendelkolben pump) or powder ring vacuum pumps.
* '''Reciprocating-type''' positive displacement: piston or diaphragm pumps.
* '''Reciprocating-type''' positive displacement: piston or diaphragm pumps.
* '''Linear-type''' positive displacement: Rope pump|rope pumps and chain pumps.
* '''Linear-type''' positive displacement: rope pumps and chain pumps.
 
===== Rotary Positive Displacement Pumps =====
===== Rotary Positive Displacement Pumps =====
Positive    displacement rotary pumps are pumps that move powder using the    principles of rotation. The vacuum created by the rotation of the pump    captures and draws in the powders.  
Positive    displacement rotary pumps are pumps that move powder using the    principles of rotation. The vacuum created by the rotation of the pump    captures and draws in the powders.  


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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]]

Latest revision as of 22:50, 3 January 2013


Screw pump

A pump displaces a volume by physical or mechanical action. Pumps fall into three major groups: direct lift, displacement, and gravity pumps.

Types

Positive Displacement Pumps

A positive displacement pump causes a powder to move by trapping a fixed amount of it and then forcing (displacing) that trapped volume into the discharge pipe.

Some positive displacement pumps work using an expanding cavity on the suction side and a decreasing cavity on the discharge side. powder flows into the pump as the cavity on the suction side expands and the powder flows out of the discharge as the cavity collapses. The volume is constant given each cycle of operation.

Positive Displacement Pump behavior and safety

Positive displacement pumps, unlike centrifugal or roto-dynamic pumps, will in theory produce the same flow at a given speed (RPM) no matter what the discharge pressure. Thus, positive displacement pumps are constant flow machines. However due to a slight increase in internal leakage as the pressure increases, a truly constant flow rate cannot be achieved.

A positive displacement pump must not be operated against a closed valve on the discharge side of the pump, because it has no shut-off head like centrifugal pumps. A positive displacement pump operating against a closed discharge valve will continue to produce flow and the pressure in the discharge line will increase, until the line bursts or the pump is severely damaged, or both.

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

A positive displacement pump can be further classified according to the mechanism used to move the powder:

  • Rotary-type positive displacement: internal gear, screw, shuttle block, flexible vane or sliding vane, circumferential piston, helical twisted roots (e.g. the Wendelkolben pump) or powder ring vacuum pumps.
  • Reciprocating-type positive displacement: piston or diaphragm pumps.
  • Linear-type positive displacement: rope pumps and chain pumps.
Rotary Positive Displacement Pumps

Positive displacement rotary pumps are pumps that move powder using the principles of rotation. The vacuum created by the rotation of the pump captures and draws in the powders.

Advantages: Rotary pumps are very efficient because they naturally remove air from the lines, eliminating the need to bleed the air from the lines manually.

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-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.

These positive displacement pumps have an expanding cavity on the suction side and a decreasing cavity on the discharge side. powder flows into the pumps as the cavity on the suction side expands and the powder flows out of the discharge as the cavity collapses. The volume is constant given each cycle of operation.

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.

Various Positive Displacement Pumps

The positive displacement principle applies in the following types of pumps: