velocity at pump inlet
velocity at pump inlet
(OP)
Hello everybody !
A quick question regarding the velocity in the pump suction pipe :
We have a water pump designed for 100 000 bbld. The water is @ atmospheric pressure and 20 - 80°C in the suction system. I would like to use a 12" pipe for suction, but the velocity would be of 2,5 m/s, and I think that I've read somewhere that it should be below 1,5 m/s.
What would be the risk tfor my pump if the velocity is too high ?
Thanks !
Daniel
A quick question regarding the velocity in the pump suction pipe :
We have a water pump designed for 100 000 bbld. The water is @ atmospheric pressure and 20 - 80°C in the suction system. I would like to use a 12" pipe for suction, but the velocity would be of 2,5 m/s, and I think that I've read somewhere that it should be below 1,5 m/s.
What would be the risk tfor my pump if the velocity is too high ?
Thanks !
Daniel





RE: velocity at pump inlet
What diameter is the pump inlet flange and where on the pump curve is the maximum duty point?
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.)
RE: velocity at pump inlet
However there is no such velocity limit as each system is different, so "it depends"... What is probably being referred to is reducing the frictional losses in the pipe, but if ou have lots of metres head and your pipe length is short, maybe it's not a problem. However 1m/sec might be too fast if your pipe is very long.
Water at 80 C has quite a high vapour pressure so you need some more metres from somewhere.
what does it depend on?
Height of liquid level above the pump (+ve) or height it is being lifted (negative)
Length of pipe and fittings
Actual temperature of the water
Elevation above sea level
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: velocity at pump inlet
But just to understand, what is the risk with the velocity ?
RE: velocity at pump inlet
If the problem is only the pressure drops due to friction then I won't worry, I have only a few dozen meters between the tank and the pump...
:)
RE: velocity at pump inlet
2.5 m/s is not that fast (~8 ft/s) so if you follow the rest of the rules (5-10x diameters of straight pipe before the suction, after any fittings like elbows or reducers) then you will be ok with some pump types, should be ok with others.
RE: velocity at pump inlet
RE: velocity at pump inlet
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: velocity at pump inlet
If the pump vendor sized it for you and the pump suction flange is 12", then the pump vendor acknowledges that the velocity will not cause problems, and they warranty the pump for those operating conditions.
If the pump was off the shelf and just slapped into this system, then you should provide some more details. There are a lot of different types of centrifugal pumps, is it vertical, horizontal? Some will be fine, some should be fine, some might not be fine.
If you already have the pump with a 12" flange and are going to use it no matter what, then you might be asking the wrong question. Calculate the losses for the 12" pipe and you are either fine, or not fine. Changing to a larger suction pipe will decrease the losses, but it will not affect the suction velocity into the pump. The suction velocity into the pump will be whatever you get with the 12" suction flange.
I take it from the original post that the 2.5 m/sec is the normal flow. A little high but not scary. Will the pump every be operated at higher flow, and if so what is velocity at that higher flow?
RE: velocity at pump inlet
My pump is single stage, single suction, radially split volute type
RE: velocity at pump inlet
I see that you are now saying that you will operate at normal conditions with half the flow.
One should carefully determine the operating conditions when installing a pump. The pump operates efficiently at the BEP. When you move off the BEP, the efficiency drops and you may end up wasting substantial amounts of energy over the long term.
If you are operating substantially away from the BEP, then the pump life may also be affected.
RE: velocity at pump inlet
RE: velocity at pump inlet
I hate Windowz 8!!!!
RE: velocity at pump inlet
Of course there is also many others - for example
adequate
enough
plenty
heaps
sufficient
should be ok
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.)
RE: velocity at pump inlet
It also has a volute cast into the block with just about the worst surface finish I have ever seen on a casting.
Needles to say, the pump inlet is 77kPa absolute (cold).
They wonder why they have cavitation damage.