Pump Suction Piping 2

[ullas2711]

Dear All,
I need to install a pump having a suction size of 3". The suction is taken from a tank and because of lack of space, it is not possible to install a 3" line. So we are thinking to install 2 numbers of 2" pipe and connect them to a 3" tee and then connect to the pump. Is it feasible to do such an arrangement? If yes what should be the minimum straght length of pipe before the suction nozzle?

Thanks in advance

 

[Artisi]

It is feasible, however, it will depend a lot on the straight run of 3" from the 3" "T" to the inlet, I would suggest that the minimum straight run is more than the "standard" 5 pipe diameters, preferably closer to 10 diameters -- plus I assume the "T" will be 3" not 2" - you also need to look at the inlet losses and the pumps NPSHr.

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.)

 

[LittleInch]

I agree, but be aware you are introducing extra resistance in the inlet piping and unless it is short and with no height difference / volatile fluid you shoud be ok, but try and use a Y instead of a tee. Parallel pipes are rarely exactly equal and hence one will flow more than the other and 2 x 2" pipes are not equal to one 3" pipe in terms of friction losses (think sum of the square of the ID).

But maybe I'm being too pedantic... go for 10D straight lenght as Artisi says. If it's more complex, draw a quick sketch with distances, flow rate, product etc.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[BigInch]

You can't install 3", but you can install 2 x 2"
That hardly seems possible. Two 2" (2.375" OD) even touching each other is still a greater distance than the OD of a 3" (3.5") Anyway....

Do you really need 10 diameters on such a small pump.
My feeling is that 5D would work OK.

Independent events are seldomly independent.

 

[Artisi]

The OP might be taking about 2 independent routes for the 2 pipes - but who knows it's all guess work at this stage.

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.)

 

[cloa]

Or simply something is in the way so the pipes can laid parallel but one big one.

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[Tmoose]

Sounds like you're contemplating violating most of the guidelines for inlet/suction design, the most basic of which is the several diameters worth of straight pipe at the inlet.

If it's a very serious pump at all the manufacturer wants the inlet flow to be treated gently and with respect and probably issues warnings like this -
"A short elbow should never to bolted directly to the pumps suction nozzle. The disturbance in the flow caused by the sharp bend so near the pump inlet may result in noisy operation, loss in efficiency, and capacity, and heavy end thrust."

http://www.pattersonpumps.com/pdf/end suction.pdf

http://www.cranepumps.com/downloadables/CATALOGS_OIPMs/Manuals & Instruction sheets/096882.PDF

rules 3 and 4 here -

http://www.pumps-filters.com/images/Rules_to_Follow_to_Avoid_Pump_Problems,_2-16-00.pdf

I'd be thinking about slow tapers, vortex breakers and turning vanes as much as maintaining area.

 

[ccfowler]

ullas2711,

To get more useful help, please provide more useful information and include a sketch of the configuration.

Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.

 

[pennpiper]

ullas2711,
What kind of pump (Positive Displacement,Centrifugal, Progressive Cavity, etc)?
What is the Commodity (Beer, Oil, Water, etc)?
What are the Operating conditions (pressure/temperature)?
What is the Design Code for this installation (ASME B31.1, B31.3, etc)?

You wrote:
"I need to install a pump having a suction size of 3"."
Normally the Tank Nozzle and the suction line is minimum one size larger than the pump nozzle. This means the Tank nozzle and the suction line size should be 4"NPS.
What is the size of the Nozzle on the Tank?

"The suction is taken from a tank and because of lack of space, it is not possible to install a 3" line."
You wrote this but you did not give any reason. This is not logical! Have you considered reversing the pump on the foundation? Have you considered moving the Pump to a new location?

"So we are thinking to install 2 numbers of 2" pipe and connect them to a 3" tee and then connect to the pump."
As already stated this is not logical. It also sounds like it would be very bad design.

"Is it feasible to do such an arrangement?"
Oh! it is feasible to do lots of things with pipe and pipe fittings but that does not mean it is good design.

"If yes what should be the minimum straight length of pipe before the suction nozzle?"
If you ask ten different pipers this question you will get ten different answers.

Can you provide a sketch?

prognosis: Lead or Lag

 

[poli60]

At the end of the day, probably, a "smooth" 2" line, expanded to 3" where feasible, would be better than the suggested solution.

 

[Artisi]

That would depend on friction losses and NPSHa/NPSHr requirements

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.)

 

[pennpiper]

ullas2711,
It has been more than a month since you posted your question and more than two weeks since you received the last response.

What did you finally do?


prognosis: Lead or Lag