Dead head pressure when the density is not water

[ER_Azza]

Hi All

A bit rusty with pump stuff. Any rotating equipment guru out there if can help me I appreciate it.

I am looking at centrifugal pump curve (Dead head at 85m)
Based on water.
However, the system I am looking at has slurry. SG at 1.25.

I remember the head don't change, pressure do. (p = 0.0981 x h x SG)

Theoretically, does that mean the dead head pressure will increase, assuming using the same motor?

 

[TugboatEng]

The dead head pressure will increase with fluid density. You may not be able to use the same motor because the power demand will also increase.

 

[Artisi]

Pump duty power will increase by atleast 25%, therefore supply current will need to be considered as well.

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.)

 

[ER_Azza]

Thanks all for the quick response.

In my case, I am looking for possible impeller re-sizing to reduce the pressure (dead head).
So using the same motor.

Current pressure is sufficient but quite near to the limit of a bursting disk after a vessel.
(Disk burst on rare occasions but did occur).

I am trying to relate the pressure on the pump curve (based on water) and to the current process which has a SG of 1.25

 

[pierreick]

Hi,
What is the issue, viscosity or density? The title of the thread is misleading.
If the issue is density, Power=Q*Ro*g*H i.e Power requirement is at least + 25%.
Please clarify.
Pierre

 

[ER_Azza]

Sorry for the wrong title thread.
The fingers were faster than the brain then.

It should be the DENSITY.

 

[LittleInch]

You have the formula in your OP.

Just re arrange to calculate head from pressure.

Viscosity does have an impact on pump performance but you usually need to ask the vendor for what that is.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

From that head curve you can calculate pressure at any point by multiplying head x density.

Power at any point = density flow rate x head.
Divide by pump efficiency to get motor power on the shaft.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[pierreick]

Hi,
To add to my previous reply to your query a handbook for pumping slurry.
Pierre

 

[Rputvin]

That looks like a pump-flo (software) curve. The sizer should have the ability to change the fluid properties to match your slurry, and then your selection and datasheet info will have information that relates directly to your application.

Not that knocking the dust off that part of the brain isn't good practice, but I'd rather convert everything over in the software vs. relying on information/methods I don't use every day.

 

[ER_Azza]

Thanks ALL

Truly appreciate the assistance & guidance.
It is slowly coming back to me.

Cheers.

 

[georgeverghese]

Bursting discs are not suitable for cases where max operating pressure is greater than 80-85% or so of BD set pressure. If so, you may have to replace the BD with conventional PSV or may be even a pilot operated PSV.
This pump curve is quite flat over the flow range around the BEP going back up to dead head / min flow, so are you saying this pump, even at normal operating flow ( which is presumably somewhere between min flow and BEP flow), produces much more pressure than you need ? A VFD can also be used to deliver less pressure at lower speed.