Length of straight pipe before the suction of pump 2

[ciise]

Hi all-

Can anyone advise on what the required length of straight pipe before inlet of centrifugal pump is.

Any link where I can look into for quidelines?





Thanks All

 

[Artisi]

Lord Kelvin - probably best known for his "balls"

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.)

 

[rmw]

MechEngNCPE never responded but maybe stanier did for him/her. I suspected as much. It is part of being separated by a common language.

To me Industrial is Pulp & Paper, Chemical, Metallurgical, Refining and Petrochemical, etc.

Commercial is more like buildings and light manufacturing, laundrys and the like.

Municipal is kind of in a world all of its own with other governmental entities.

When I worked for a British company, their use of the word "industrial" meant what "electric utility" does in the states.

In what I define as Industrial, I have never seen the use of suction difussers. And I would add to that that I have never seen them in Electric Utility applications as well. I have, however seen them in building systems and municipal applications and maybe the occasional steam laundry.

rmw

 

[Artisi]

Just to get away a little from the norm, for pulp and paper when pumping 4% or more consistency and especially as you get to 5 - 6% you need anything but smooth flow into the pump inlet, the more agitated the better to ensure the stock is not dewatered at the pipe/pump reducing inlet, but this can be another discussion in another thread if anyone is interested

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.)

 

[Spud6414]

The tendency to overthink things is common amongst all of us. In my many years as a pump mechanic on all types of pumps there are some things I have learned. The same pump used in any setting be it heavy industry, commercial/municipal is the same pump. It may get treated very differently in regards to maintenance and so on.

Suction diffusers are handy when one can not meet the recommended pipe diameter and straight run before suction end mating. However as another poster stated Diameter is as important if not more important then straight pipe length. Industry norm depends completely on the industry. Having seen many things some of them very unusual yet they worked. In Power Generation we like 5 times the diameter for straight run and one and half times suction for diameter with an eccentric reduction.

All of this can be found in the various handbooks and lets not forget that all of this is a moot point if NPSH is not met.

 

[Artisi]

Spud6414, a good reply, many times it is useful to get back to basics and as you stated "The tendency to overthink ......." can be a problem.

Worth your first star.

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.)

 

[rmw]

I have rarely seen a pump fail from overthinking, but I have seen many suffer and/or fail due to not thinking about all that is required to make the installation successful.

rmw

 

[Artisi]

Depends what you are thinking.

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.)

 

[Spud6414]

rmw, I agree completely, that falls under many strange things I have seen

Sometimes one really wonders what someone was or was not thinking.

Spud says; Meticulous effort and willingness to learn are honorable traits.

 

[stanier]

I have seen many pumps fail because of overthinking. Generally it is senior engineers or management thinking they need to add 20% to the duty as a safety factor. This leads to pumps being oversized and running well to the right of BEP. This leads to vibration and failure of seals and bearings.

In respect of suction design instead of just using Sank's Pumping Station Design, ANSI/HI 9.8 or the US Army references on the subject engineers try and think of ways of designing pump suctions. If only they stopped "thinking" and tried ways that have worked for decades the problems would not arise.

I have seen many a pump design modelled using FEA only to see the same solution that would have taken 5 minutes of reading.

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

http://waterhammer.hopout.com.au/

 

[Artisi]

Stanier,
I would suggest that pumps that have been oversized by "others" normally run to the left of BEP as a result of being throttle back to reduce flow to the real system neeeds. Further, being oversized also impacts on pipeline sizes, motor sizes etc.

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.)

 

[Spud6414]

NPSH... Oversize pumps. Bad Idea.

Spud says; Meticulous effort and willingness to learn are honorable traits.

 

[rmw]

While I don't disagree with the scenario that stanier presents, I wouldn't classify that as overthinking, rather I would postulate that it is not thinking at all. Moreover, I'd call it brainless.

And I have been a victim of it, and have been guilty of deliberately undersizing equipment, pumps included, because I knew that some anal superior was going to brainlessly add his/her "fat" no matter what was done in the initial sizing.

The bad scenario is when there are several steps up the approval ladder and everyone up the ladder adds some "fat" because they don't have the ability to think through what the engineer has (or has not) done with respect to doing their job and sizing the pump correctly in the first place. Because of this fubar, as an example, while not a pump per se but closely related, I have seen actuators with 3" output shafts coupled to driven devices with 1" input shafts. There is a mismatch. Someone added too much fat somewhere and I hold that that is brainless.

rmw

 

[PBtoAU]

The rule of thumb I've used in the past with good success is: One pipe diameter of suction straight-run for every fps of suction line velocity. Usually this is about 5 diameters, but in some cases, velocities may necessarily be higher or lower.