System curve- Screw Pump

[Lan123]

I am curious to find out how I could draw a system curve for a screw pump. Let’s say at a wastewater treatment plant there is an archimedes screw pump that transfer sludge between two sumps. So the static head will be the difference in sludge levels at the two sumps. Then what about the friction head? How do I calculate this?

Thanks

 

[DubMac]

Hey Lan123,

The system curve is independent of the pump that is used; other than velocity head change (usually very minimal).

It is made up of 2 main components: Static head and Friction losses.
Static head would be comprised of 2parts: elevation change and Pressure difference between supply point and delivery point.

Friction losses are comprised of actual friction losses in piping system. They also are comprised of entrance and exit losses, and difference in velocity heads between pump suction and discharge. For most cases the velocity head portion can be ignored as they are typically very minimal.

The static head in your case looks like it would just be elevation.

The friction losses in the system can be calculated using any of the many published "friction loss" tables for all piping, valves, other components in the system.

A very good approximation is usually found by assuming the friction losses increase as the square of the increase in flow. and can be plotted as thus.

Curve would start at 0 flow on X axis and at the static head value on the Y axis. From there, head increases as the square of the flow increase.

Remember this is a close approximation, and to be perfectly accurate, you really should go through the exercise of calculating the actual friction losses using tables and actual piping/ components.

Since this is sludge, you will need information as to the approximate viscosity and other fluid characteristics of the sludge since the friction tables are generally based on water. Sure you can find this in a water/wastewater publication somewhere.

 

[Pumpsonly]

From my understanding ,an archimedean screw pumping installation will perform only static lift. It does not pump through a piping system and so do not have friction losses for the system curve.
The pump mechanically lift the sludge by the rotating action of the screw blades from a lower to high level.

 

[Strong]

Here is a link to information that may help:

http://www.water.siemens.com/en/pro.../screw_pumps/Pages/microfloc_internalift.aspx

I have worked on these machines.

Walt