Differential Pressure

[YoYo2000]

I received a datasheet with suction pressure the same as minimum, rated, and maximum. However the discharge pressure is different for all the min/rated/max pressure. For the same fluid and shaft speed, can the differential pressure be different?

 

[LittleInch]

For a centrifugal / axial pump Yes, but only within a certain range - approx 20% from max to min, but could be more for different types of pumps.

You've "received" it. For what purpose?

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[YoYo2000]

Sorry, not received, but I have a pump datasheet which had this information on it. Why would there be a little difference with the discharge pressure if we dont increase or decrease the suction pressure?

 

[1gibson]

Change in flow

 

[LittleInch]

Basically cetrifugal pumps are "constant" pressure pumps whereby the discharge pressure, based on a fixed inlet pressure only varies a small amouunt for quite a wide variety of flow. Search on "pump curve" on this forum to see what I mean.

Positive Displacement Pumps (piston, screw, diapharm etc) are essentially "constant" flow pumps whereby the flowrate only vares a small amount for quite a wide variaiton in outlet pressure.

Centrifugal pumps work on differential head so if the inlet pressure goes up, the discharge head goes up by a simialr amount for the same flowrate.

If you posted the data sheet we might be able to help you a bit more, but I hope this gives you something to work with as it's a pretty vague question at the moment.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Artisi]

On your data sheet, what are the flow rates corresponding to the different discharge pressures??

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[Pumpsonly]

You did not mention it is a process data sheet of mechanical data sheet. The process data sheet is prepared by the process engineer. It just specified what is the process requirement on the flow and discharge/diff. pressure under different conditions. The mechanical engineer/pump engineer will select/propose the suitable pump type to meet the requirement.
If the difference in the DP is very wide range, a positive displacement pump or a centrifugal pump with VFD may be selected.

 

[BigInch]

If you received it on a data sheet, it is probably your job to determine what pump can provide the required differential heads for the entire envelope of operating conditions. There is no reason that, if the pump can do the worst case, it would not be able to encompass the other operating conditions within its entire operating envelop.

Independent events are seldomly independent.