3 replies to this topic

[krishnamurthy]

when the outlet of the centrifugal pump is closed, the pump cannot develop more pressure. while in case of positive displacement pump when the outlet valve is closed the pump can develop more pressure so PSV is required to protect the downstream piping and pump. 

 

How the centrifugal pump cannot develop more pressure while positive displacement pump does when the outlet valve is closed? Please explain in detail, i searched online but still i am not clear with this.

[fallah]

when the outlet of the centrifugal pump is closed, the pump cannot develop more pressure. while in case of positive displacement pump when the outlet valve is closed the pump can develop more pressure so PSV is required to protect the downstream piping and pump. 

 

How the centrifugal pump cannot develop more pressure while positive displacement pump does when the outlet valve is closed? Please explain in detail, i searched online but still i am not clear with this.

 

Hi,

 

In brief, the centrifugal pumps at dead head conditions are subject to internal recirculation then cannot develop the discharge pressure more than shut off value; while in positive displacement pumps there is no room for internal recirculation at dead head conditions and there would be pressure increment per each stroke...

[farid.k]

Actually the answer is at the pump name itself. The name of the pump tells the concept of how they transfer the fluid.

 

Centrifugal- using centrifugal force. This centrifugal force will develop when impeller rotate and caused the fluid to collide with pump casing, and caused the pressure developed. Configuration of the centrifugal pump has some hollow space in between impeller and pump casing. So if the discharge is closed, the impeller is still running but the fluid will be move backward as there is hollow space in between impeller and pump casing. We call it as pump running at shut off pressure.

 

for positive displacement- i.e. piston pump, the pump operate by displace a specific amount of fluid and if you look at the configuration, there is no chance for the fluid to move backwards as there is no space in between piston and casing. If there is some backflow, the flow is very2 small (negligible). That is why the pressure will keep build up as the piston move (as there is no chance the fluid to move backward as the piston move, that specific amount will be forced to move to the front).

 

So this is from my understanding only. Appreciate others to comment/add

[samayaraj]

Hi krishnamurthy,

 

see this link where i explained your question earlier...

 

http://www.cheresour...mps/#entry83433

 

 

#Samayaraj