Running pump in reverse flow

[keyhanafshar]

Hi There,

Have anybody experienced reverse flow in a running pump? I have been told by plant operator that once he finished unloading first compartment and remove the empty suction hose to next compartmnet there was product flowing back through pump suction and cause spill. Pump was unloading product from truck to above ground tank with 15meter height when this happened. Pumpe can make 16 meter head. Please somebody tell me how this back flow is possible while the pump is running??

 

[ione]

Never heard of check valves?

Nothing new under the sun. Centrifugal pumps may experience reverse flow in event of sudden power cut to the pump driver and where the check valve fails (or it’s not present at all) .
The pump speed reduces quite rapidly (low inertial force of rotating parts) until the pump is not capable to overcome the system head. It’s at that point the flow direction reverses and passing from discharge to suction side.

 

[hydtools]

The suction hose was not empty and the remaining product backflowed.

Ted

 

[waross]

I'll agree with hydtools.
Or the pump was not actually running. The size of the spill may be an indication. The lost volume of a suction line spill may be equal to the volume of a few feet of suction line. If the pump was actually off the spill volume will be greater and will be related to the volume of the discharge line up to the highest point.
Was this a centrifugal pump or a positive displacement pump?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[keyhanafshar]

Yes the pump was running as per truck unloading procedure, oonce a compartment is empty operator is disconnecting the hose from that compartment and connecting to next one, while doing this there was gravity back flow from higher pressure side ( 15 meter product head in the tank) toward lower pressure. My question is how liquid can pass through a running impeller and find its way to the suction hose and cause a spill. As i said this is the procedure used for more than 30 years. The only difference is the said pump is much smaller in size comparing to others. I am thinking of increased clearances between wear ring and eyelet possibly.

 

[stanier]

Search for "four quadrant" data. This will explain the state of a centrifugal pump that may need to be considered in any surge anaylsis. This includes reverse flow when the pump is running.

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

http://waterhammer.hopout.com.au/

 

[Artisi]

And the question was - Quote "Have anybody experienced reverse flow in a running pump?" unquote - not reverse rotation of the pump from reverse flow.



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.)

 

[Ziggypump]

Centrifugal pumps have what is called Net Positive Suction Head. Means pressure needs to be applied to the inlet of the pump for the pump to work. If this pressure is not met, then no matter how fast the impeller is spinning, fluid will not flow, and will flow back to balance the pressure in the pipe.

Check the NPSH and the elevation of the feeding pipe. If the NPSH is 2 ft head, then the pipe needs to be full a minimum of 2 ft to prevent back flow.

 

[BigInch]

Its not reverse flow, its "blowback". Hi pressure in the discharge can easily overcome pump friction when there is no or little forward rotational power.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus