7 replies to this topic

[farid.k]

hye all,

 

 

I don’t know whether this has been discussed or not before. But I did searched and I didn’t find what I really want and I don’t know the keyword to write. This is regarding to the positive displacement pump working philosophy. As we know, for the positive displacement pump running theoretically will be independent of discharge pressure which means that the pump will keep on pumping and the pressure will keep on increasing if there is any blockage at the discharge until the relief valve pop-up or any internal parts of pump or discharge system failed. Am I correct?

 

The questions are:

 

What parameter need to check if existing positive displacement pump need to be relocated to a new location and there is a very significant pump discharge piping modification which is additional 300 meter piping length. Does the pump will be adequate to deliver liquid at new location? Based on the working philosophy above, it should be adequate to do so isn’t?

 

What happened if due to the significant additional pipe length, the pressure drop increased and exceed the discharge pressure stated in the pump datasheet AND also the set pressure of relief valve?

 

For centrifugal type, it is common to see the minimum flow line. For the PD pump, normally don’t have the minimum flow line isn’t? If yes can I know why or what is the reason?

[breizh]

http://www.pumped101...cs_displacement

 

You may find what you are looking for reading the documents attached.

Good luck.

Breizh

[latexman]

Check the backpressure at pump discharge and motor size.

 

Increase line size or relocate pump or change to new pump or add a second pump.

 

A centrifugal pump operates on it's pump curve from minimum flow to end of the curve.  Some call it a (relatively) constant head machine.  A PD pump is a constant volume machine.  That is very different.

[farid.k]

Check the backpressure at pump discharge and motor size.

 

Increase line size or relocate pump or change to new pump or add a second pump.

 

A centrifugal pump operates on it's pump curve from minimum flow to end of the curve.  Some call it a (relatively) constant head machine.  A PD pump is a constant volume machine.  That is very different.

Dear latexmen,

 

The backpressure is remain same. The pump is actually for the firewater foam injecting the foam to the fire water line via balanced pressure proportioner device. The issue is the new additional pipe routing is quite long and it is about 300 meter additional. I trust that it will cause a quite significant additional pressure drop. What say you?

[latexman]

I get the feeling I do not understand your application.  There is an additional 300 meters of discharge pipe, but the backpressure does not increase!  I do not understand that for a PD pump.  Maybe a sketch or more details can help us help you.

[farid.k]

I get the feeling I do not understand your application.  There is an additional 300 meters of discharge pipe, but the backpressure does not increase!  I do not understand that for a PD pump.  Maybe a sketch or more details can help us help you.

dear latexmen,

 

i mean back pressure from fire water will remain same. yea i do agree with you that "build-up" back pressure will increase due to additional piping. sorry for the error. will upload the sketch asap.

[farid.k]

I get the feeling I do not understand your application.  There is an additional 300 meters of discharge pipe, but the backpressure does not increase!  I do not understand that for a PD pump.  Maybe a sketch or more details can help us help you.

dear latexmen,

kindly refer sketch

Attached Files

•  20150921103640.pdf   18.94KB   23 downloads

[latexman]

I see now.  If you calculate the pump can deliver the design flow rate of foam concentrate to the IBP's, considering recirculation back to the foam concentrate tank (i.e. backpressure at pump discharge is not excessive), then the new location and pipe and fittings size is okay.