Difference between revisions of "Powder Pumps"

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[[Image:Jet_pump.jpg|thumb||right|A jet pump]]
[[Image:Jet_pump.jpg|thumb||right|A jet pump]]
[[Image:Lysholm_screw_rotors.jpg|thumb|upright|Screw pump]]
[[File:220px-Rotary_vane_pump.svg.png|thumb|Rotary vane 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.
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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.


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 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.
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]]
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 Positive Displacement Pumps =====
===== Rotary Positive Displacement Pumps =====
[[File:220px-Rotary_vane_pump.svg.png|thumb|Rotary vane pump]]
 
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.  


'''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.
'''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.
'''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.




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