sediments in suction pipe 1

[Prototyp]

7 pumps are supplied by a common DN500 suction pipe (figure). Medium is a slurry of oil and small metal scarfs. What happens to the pumps if the size of the common suction pipe is reduced due to sediments in the pipe?

 

[Artisi]

It could lower the available NPSH to a dangerous low level resulting in pump inlet cavitation, however there is insufficient information available for anyone to start any discussion.

A full hydraulic engineering study is required to come up with any meaningful answer.



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.)

 

[LittleInch]

I'd go with that.

Clearly there is also a risk that a chunk of the "sediment" will break off and enter the pumps as a block or completely block the inlet line to the pumps.

There is also the issue that the resistance to flow to the further pumps becomes out of balance compared to the pumps nearest the entrance pipe and hence the pump flow could become unbalanced.

Also note that the individual inlet lines are top flat with reducers and hence the inlet lines themselves could become blocked with sediment from header up to reducer....

Those valve handles look difficult to operate while we're at it.

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

 

[cvg]

if you are trying to pump the scarfs, than design your system with higher velocities. otherwise, provide a sump where you can collect them and remove periodically.

 

[JJPellin]

We see this in our decoking water pumps. Built up solids can be sucked into the pump, lodging in impellers, causing imbalance and high vibration. In one system, we have a time based task to flush the suction line to a lower pressure sump at high velocity. In another system, we back-flush the line with fire water to dislodge the accumulated solids.

Johnny Pellin

 

[georgeverghese]

Agreed, rather than reducing the common feed manifold pipe dia, why not install a few timer activated live drain full bore metal seated 3/4inch control valves at the bottom of this DN500 manifold to flush out the settled metal bits?

 

[Prototyp]

Thanks for comments so far.

The pumpes are especially made for slurries and quipped with wear resistant ducted impellers. So they should be capable to take a hit from loose breaking sediments. If sediment builds up the flow velocity will increase anyway due to decreased cross section of the DN500 pipe. My main concern is cavitation caused by a higher inlet velocity.

A drain in the manifold could be an approach. Changing the hole arrangement would be very expensive. Are there any information available how such a hydraulic study is done?

 

[Artisi]

do you currently have a problem or are you pre-empting anticipated problems?

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.)

 

[Prototyp]

It is a new facility which is operating right now with apr. 10% of its capacity. Currently there are no problems concerning this piping. But sedimentaion is rather a process that might happen in the long run. I am trying to estimate the risk that this will happen.

 

[bimr]

With a pipe manifold like you are describing, it is common practice to neck down the size of the manifold as the manifold proceeds past the pump inlets.

 

[SandCounter]

You could run a loop from one of the pump discharges to a small line within the manifold toward the bottom with orifices or nozzles to agitate the sediment. Valve it and add a flush regimen to your process.

I used to count sand. Now I don't count at all.

 

[mk3223]

Agreed with SandCounter, a close loop of the suction flush could be helpful for the potential sediment problem.