Are there issues with operating a pump barely above its minimum flow? (see attached pump curve)

[pa5tabear]

Are there problems with operating near the "minimum required flow for safe pump operation"? I assume that below this level you start getting into the dead-head regime. Is there also lesser risk with operating near the minimum, but above?

We are debating whether or not to add a small size pump to our multi-pump setup. The energy savings do not justify its cost, so I'm wondering if there are other lifetime costs to consider.

Link

 

[DubMac]

Yes

 

[BigInch]

Plenty of issues. Ideally you would not want to operate below 50% for extended periods of time (only during start up or shut down). Expect maintenance costs to increase the farther you go outside of the 70-80-100% range.

Independent events are seldomly independent.

 

[Artisi]

A "roto jet" pump is a completely different animal to a centrifugal pump as there is no impeller subject to varying radial loads as the pump moves away from from BEP, therefore the constraints of a centrifugal pump operating either left or right of BEP do not comply.
Not my field of expertise but from what I understand the minimum flow line is the minimum allowable flow, therefore operating above minimum line should be OK.
Why not check with the manufacturer, surely this should be the first phone call to sort your concern.

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.)

 

[BigInch]

Minimum flow is where going under that flowrate tends to cause recirculation within the pump and resultant heating/overheating/vaporization of the fluid. Maintenance difficulties can begin very far above that.

Independent events are seldomly independent.

 

[TenPenny]

As noted above, this is a Roto Jet pump, so anything said in reference to centrifugal pumps is quite likely not applicable.

Other than walking past several of them, I haven't had much to do with rotojets, so I suggest you keep hunting for someone with some practical experience.

 

[BigInch]

Is there some reason that all of a sudden some are talking about rotojet pumps? I missed that.

Independent events are seldomly independent.

 

[BigInch]

Got it "Link". I figured that was some "Linked-In" URL and thought the OP forgot to post the curve. Sorry.

Independent events are seldomly independent.

 

[ccfowler]

Is the existing system an arrangement of several RotoJet pumps in parallel, or is this RotoJet being considered for the proposed low flow duty? If there are already several RotoJets in parallel, then the system must have an astounding turn-down ratio for operation if it can't be satisfied by going from several pumps at full flow to only one at minimum flow.

I've never dealt with multiple RotoJets in parallel, but given their manner of operation, I would want to verify that all are sharing the total flow in their proper proportion. My thinking is that just one pump operating at the minimum system flow condition may not be as severe a problem as initially anticipated. The accuracy with which the minimum and maximum flows are known seems to be the key to resolving this question.

Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.