Why some SPECS ask pump operation to the left of the BEP? 1

[billbusy]

PER API 610, 70%-120%of BEP for prefered operation range. But in our company's spec, it is preferred pump operation to the left of the BEP which means 70%-100%.

Any body can explain a little bit? Thanks.

MSc. Mechanical Engineering;
5 years EPC experience;
Oil & Gas industry in Canada.

 

[PumpSmart]

Reliability goes up between 70-120% BEP.
Hydraulic and vibration, seals, bearings problems decrease in this range.

That is because design of pump ocurrs at BEP.

I hope this helps.

 

[Artisi]

Selecting a pump to operate slightly left of BEP can be a good move if the calculated head has had a margin added "just to be sure", the over estimation of head will result in lower head moving the operating point to the right and closer to BEP. Or, if and it usually happens, the operators / owners want increased capacity it will mean that the new duty point will not move too far right of BEP, or staying left of BEP usually means NPSHa is less and any increase in flow doesn't impact so much on NPSHa or, someone doesn't know what they are doing.

Why don't you ask the spec. writer WHY? That should solve your problem.

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]

It is both for maintenance and a better possibility of accomodating future capacity increase.


Independent events are seldomly independent.

 

[PumpSmart]

mmm, In case of accomodating future capacity increase, i think it is better to try to estimate this value to know impact on pump.

 

[BigInch]

It's simply saying don't design it at 100-120%. Its not saying that it can't operate there ever. So the future capacity estimate is around +20% max. Most of that comes nearly free anyway.

Independent events are seldomly independent.

 

[rotw]

Any more info on the type of API pump we are talking about ?

ps: For Waste water submersible pumps (so not API), it is very common that the pump is selected to operate at left of the curve (50- 60% of BEP).

 

[1gibson]

It will also reduce head rise to shutoff.

Be careful with the terms "operate" and "design." If you tell a pump vendor to design for left of BEP, you might not have the NPSH or motor HP covered for flows higher than BEP. Which defeats the purpose, if the intent of the spec was to have flexibility for future flow increase with the equipment.

Operation left of BEP is what you say the spec says, that's fine, pick a slightly larger pump. But "Preferred operating region" (OP said range, I assume it was meant to be region) is a term that has a definition in API. Paraphrasing, it is the flow range that the pump must pass base limits of vibration at test (there are higher limits for "allowable operating region.")

The range of BEP that is used when selecting a pump is 80-110%. This is specified in API, but does not have a firm definition. It sounds like the spec limits this to 80-100%. That is what it means.

Even if everyone understands the intent, one word can change a lot in a specification.

 

[Softedge]

in addition to the reasons stated above, a pump will run with greater stability and predictability when operated left of the bep, than to the right of bep. now here's something to consider; as the pump wears it will operate left of where it operated when new. if you operate just to the right of bep when new, as the pump wears you will move left on the curve and pass through bep. here's the next problem; most designers do not understand the systems they are designing well enough to calculate the actual heads the pump will see at the design flow rate, so they apply factors to friction losses, factors to system requirements, factors for pump performance and then factors for motor horsepower. all of these factors result in the recommendation to run left of the bep. what we should be doing is taking the effort to understand the systems we are designing to calculate as close as possible to the actual conditions and selecting a pump to run on or just right of bep. the only place we need to apply a factor is motor horsepower.
regards,
arthur stack
softedge=innovation