Pump Cavitation
Pump Cavitation
(OP)
Hi,
We have a pump connected to a tank at our work place, the problem is, the pump's base is orinted such that an elbow is required to connect the pump to the tank. the pump is cavitating quite heavily. i believe there should be sufficient suction pressure available. but the pump is still experience cavitation. can the elbow alone be responsible for causing cavitation, due to uneven flow? Is the reason why elbows are not recommended at the suction end of a pump purely due to head loss, or can the shape of an elbow cause uneven flow or bubbles.
Thanks is advance
We have a pump connected to a tank at our work place, the problem is, the pump's base is orinted such that an elbow is required to connect the pump to the tank. the pump is cavitating quite heavily. i believe there should be sufficient suction pressure available. but the pump is still experience cavitation. can the elbow alone be responsible for causing cavitation, due to uneven flow? Is the reason why elbows are not recommended at the suction end of a pump purely due to head loss, or can the shape of an elbow cause uneven flow or bubbles.
Thanks is advance





RE: Pump Cavitation
You can purchase an elbow (or add to existing) turning vanes, but you are probably stuck with the configuration so I won't suggest correcting it. Google images "pipe elbow turning vanes."
RE: Pump Cavitation
Its a PD pump
RE: Pump Cavitation
A PD pump cavitating "quite heavily" would probably pulverize the pistons (in a plunger pump) or destroy the stator (in a PCP) within a few hours. Are you sure you don't mean "vibrating" instead of "cavitating"?
David Simpson, PE
MuleShoe Engineering
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"
RE: Pump Cavitation
Good luck,
Latexman
Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers
RE: Pump Cavitation
Johnny Pellin
RE: Pump Cavitation
You say you "believe" there is sufficient suction pressure. If you give us the fluid, its vapaour pressure (sometimes called Reid Vapour Pressure or RVP) at the temperature you are pumping at, your elevation above sea level, minimum liquid level above the pump, sketch or description of the inlet piping (size, length, number of fittings) and flowrate we might be able to check this and see where the issues lie. Temperature can be very importaant - has this only just started or is it a new pump?
Otherwise I agree with the posts above, an elbow close to the pump is not normally recomended, but as many of these issues are velocity related, an option may be to increase pipe size as much as possible up to the pump and then reduce down (concentric reducer). Another option is a flow straightener or flow conditioner plate which I have seen used before where there is not enough room for 5 to 10 D of pipe going into the pump (google image - ISO flow conditioner ).
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Pump Cavitation
Good luck,
Latexman
Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers
RE: Pump Cavitation
Thanks for all the replies!
Im new to this forum and new to engineering aswell. so please forgive my ignorance and lack of knowledge.
I looked at other pumps in the area and they are all running fine, they have the same configuration, and roughly the same amount of piping from the tank to the suction, but they do not have elbows. so i assumed that 1 elbow would not impede the NSPH too much.
So i tried to do the calculations, and i am getting numbers that do not make sense. this is my first time calculating pressure heads and head losses so please bear with me.
on the first page of the attachment you can see a drawing of a tank. ignore the "assume 10, 5, 1m" . i looked at the tank data, and it is usually at 10m level above the level of the pump
So our available head pressure available should be 10 m
so now i needed to calculate major and minor losses. to do that they require velocity.
So using the equation
V=2gh
V=196m/s (too high?)
so using that velocity and calculating the head losses meant the losses were way too high, so high in fact that they were greater than the available pressure head. so i think my mistake is at this step. for calculating velocity.
I would really appreciate your help
some more data that i have
liquid temp-175 C
SPEC GRAV- .91
VISCOSITY; 60 cS
RE: Pump Cavitation
RE: Pump Cavitation
Velocity is volumetric flowrate per second divided by cross sectional area all in metres.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Pump Cavitation
Good luck,
Latexman
Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers
RE: Pump Cavitation
David Simpson, PE
MuleShoe Engineering
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"
RE: Pump Cavitation
I work as well with pumps in a refinery, and an elbow just before the suction flange can lead to turbulence and noise very easily. If the flow is high, and therefore velocity in the pipes is high, it leads to turbulence and consequently noise. If flow is not eough high, turbulence is more diffuclt to occur. But these are not due to cavitation, they are due to an fast change in the direction of the fluid in the suction of your pump, then leading to turbulence.
I would recommend you to try to decrease flow and chek if it stops in an lower flow.
If the flow is high, a pipe elbow turning vanes may be a good idea.
Good luck!
RE: Pump Cavitation
The only problem I have is blockage suction strainer with dirt or sludge. So, please look at your liquid. Is there any possibility to form sludge after you loading the liquid into the tank?
Once again please look at your pumping liquid too (liquid temperature, etc). It is extremely important.
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RE: Pump Cavitation
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.)