So, what about the BEP?
So, what about the BEP?
(OP)
We have been running a lot of centrifugal pumps (liquid nitrogen service) through the repair shop. I began reading up on centrifugal pumps and discovered the BEP (best efficiency point). I also learned how a pump can be damaged if one strays too far to either side of this point. Here are a couple of questions.
How close should one stay to the BEP to avoid damage? Is the safe range symmetrical about the point (assuming efficiency vs. flow is on a separate curve)?
To satisfy my curiosity, I took a pump curve with me to the field and watched part of a transfer. The suction gauge read 15 psi and the discharge read 35. My curve had a statement on it "Shut down pump if differential pressure drops below 23 psi." I mentioned this to one of the techs. Let's just say he was skeptical.
I do think people are right when they say most pump problems are due to bad operating practices. I plan to suggest some changes to operating procedures, but I have a feeling I'll run into quite a bit of resistance.
How close should one stay to the BEP to avoid damage? Is the safe range symmetrical about the point (assuming efficiency vs. flow is on a separate curve)?
To satisfy my curiosity, I took a pump curve with me to the field and watched part of a transfer. The suction gauge read 15 psi and the discharge read 35. My curve had a statement on it "Shut down pump if differential pressure drops below 23 psi." I mentioned this to one of the techs. Let's just say he was skeptical.
I do think people are right when they say most pump problems are due to bad operating practices. I plan to suggest some changes to operating procedures, but I have a feeling I'll run into quite a bit of resistance.





RE: So, what about the BEP?
Going the Big Inch!![[worm] worm](https://www.tipmaster.com/images/worm.gif)
http://virtualpipeline.spaces.msn.com
RE: So, what about the BEP?
provided that the gauge readings are reasonably accurate, the fluid properties are near design conditions, the pump rpm is near design condition, & the pump impeller diameter is at design conditions, then operating that pump with that low of differential implies a higher flow (i.e. operating point to right of bep). thus, a higher requirement of npsha for the pump to operate without cavitation. what sort of damage has been done to these pumps?
a website to aid in your diagnosis and educate you, other than this one is at:
http://w
the author has many articles that you may find helpful.
like BigInch states, operating the pump outside of the mfg recommended flow range (i.e. min/max continuous flow range) is not healthy at all.
good luck and we'll be glad to further assist you.
-pmover
RE: So, what about the BEP?
RE: So, what about the BEP?
Going the Big Inch!![[worm] worm](https://www.tipmaster.com/images/worm.gif)
http://virtualpipeline.spaces.msn.com
RE: So, what about the BEP?
In addition to what has been said concerning instability effects (vibration, hydraulic thrusts, shaft deflection, resulting in premature bearing and mechanical seal failures) when working away from the BEP, one can also consider that since this is cryogenic service operating close to the boiling point of nitrogen, any loss of efficiency would probably induce vaporization and vapor binding and even separation cavitation.
Beside the non-symmetrical forces appearing when working to the right or left of the BEP, thermal expansions and contractions may affect the internal dimensions of the moving and stationary pump components. Thus, many users prefer to operate within 80 to 110% of BEP for optimum performance.