PUMP SUCTION WITHOUT REDUCER 3

[jsn1980]

VERTICAL LPG PUMP IS DESIGNED ACCORDING TO API 610 10TH EDITION

AS PER PUMP VENDOR DRAWING,
PUMP SUCTION NOZZLE SIZE 6", PUMP DISCHARGE NOZZLE SIZE 4"

AS PER P&ID
PUMP SUCTION LINE SIZE 6", PUMP DISCHARGE LINE SIZE 6"

IS POSSIBLE PIPING WORK CAN BE DONE WITHOUT REDUCER AT SUCTION NOZZLE ? (SINCE SUCTION NOZZLE SIZE AND SUCTION LINE SIZE ARE SAME)

IN MY EXPERIENCE PIPING LINE SIZE ALWAYS ONE SIZE GREATER THAN NOZZLE SIZE.

 

[LittleInch]

Yes it is. Reducing size is more often when there is more than one pump in operation at any one time but if 6" is OK in terms of pressure drop then it is ok.

Please don't use CAPITALS - it's regarded as SHOUTING - and please don't double post

My motto: Learn something new every day

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

 

[pennpiper]

jsn1980,
You do not use a reducer in a pump suction (or any other line) because it is a mandatory requirement to have a reducer, you only use a reducer when there is a change in the line size.

Don't over think it!

prognosis: Lead or Lag

 

[cvg]

I would recommend not ever using a reducer on the suction nozzle if you can avoid it

 

[Ripz]

cvg,

Why not? Almost every pump i've come across has suction reducers.

 

[pennpiper]

Ripz
You wrote:
"Why not? Almost every pump i've come across has suction reducers."
Yes but ONLY because there was a change in pipe size.




prognosis: Lead or Lag

 

[1gibson]

Many specs require suction piping to be one size larger than the pump's suction flange (e.g. 10" flange, 12" suction line with reducer to 10") hence the reducers being common.

Vertical can pumps are not at all sensitive to suction line conditions, provided the pressure drop is not severe enough to reduce the NPSHA beyond what was specified to the pump manufacturer. Maybe if the barrel is extremely short it could be an issue, in that case there should be plenty of NPSHA and a vertical pump might not be the best choice.

The typical rules for straight pipe length of X diameters, no elbows directly before the flange, etc. have no effect (it is negligible) because the fluid falls down into the barrel and stabilizes before entering the impeller.

Much different for a horizontal pump, where the suction piping will affect the fluid conditions entering the impeller.

 

[Ripz]

I'm no pump designer, but i'm pretty sure they put reducers for a reason. Not just because the pipe sizes are different.

 

[Ripz]

So, Since i'm no expert i did some research and to summarise and quote.

"The reducer on the inlet side of a pump ensures that the velocity of liquid in the suction line is slowed sufficiently to provide a smooth flow of liquid with minimized friction losses in the line to ensure as high as possible an NPSH available from the system.

The increaser on the discharge side of the pump is designed to increase the pipe diameter from the pump nozzle to reduce the velocity of the liquid in the discharge line in order to reduce the total head the pump is required to develop to operate the system."

 

[Compositepro]

Ripz, your quoted statement is so misleading that it is almost nonsense (probably because it is taken out of context). Try using a little common sense. Suction piping is often made larger to reduce pressure drop in long suction lines. This is what requires a reducer to be used at the pump. This is also why pumps are placed at the starting end of a pipe rather than the other end. It is not the reducer that slows velocity (quite the opposite), it is the larger pipe.

 

[1gibson]

They do put reducers on just because the pipe sizes are different; how/why else would you use a reducer?

The pipe sizes are different for a reason. Sometimes the reason is general best practice, and doesn't matter on a specific installation.

You can blindly follow best practices (nothing wrong with that) or you can ask why, but you can't always do both at the same time.

 

[jsn1980]

Thanks for All Reply..

And also i discussed with my process and machinery department,

suction line size 6" according to process requirement. and Suction nozzle size 6" according to pump vendor requirement.

So, Reducer is not required. hence both size are same (i.e reducer is not mandatory at Suction side)

 

[macmet]

I am far from a pump expert, but I thought generally the discharged suction connection was one size larger than the line to reduce the velocity of the fluid through the pump. Is that not the case?

 

[pennpiper]

macmet,
You wrote:"I am far from a pump expert, but I thought generally the discharged suction connection was one size larger than the line to reduce the velocity of the fluid through the pump. Is that not the case?"

You might want to do a little homework studying piping systems and process equipment.
a/ there is no such thing as "discharged suction connection" There is a pump suction nozzle which is sometimes referred to as the pump inlet. There is also a pump discharge nozzle sometimes referred to as the pump outlet nozzle.

b/ "connection was one size larger than the line to reduce the velocity of the fluid through the pump." I have lot worked on every pump system in the world but in my 45 years of actively working in the process plant engineering and design profession I have never come across a situation where the "connection was one size larger than the line to reduce the velocity of the fluid through the pump." I just did not happen.

What ever you read or heard someone say, it was wrong or you misunderstood it completely.

prognosis: Lead or Lag

 

[Pumpsonly]

It does not have to be a pump expert to decide whether a reducer / enlarger is require at the pump suction or discharge.
All it need is common sense. The piping size are determine by the limit of flow velocity through it as the losses is proportional to the velocity ^2.
Therefore for a given flow rate, the larger pipe dia. = lower velocity = lower friction losses = lower required pump diff. head= lower running cost. For the suction pipe size, NPSHA will be a major factor. For the discharge piping sizing, a balance has to be made between capital cost and running cost.

When the piping engineer decided on the pipe sizes, he probably have no idea of the pump suction and discharge size.
And very often, the pump nozzle sizes varies with different pump makes even for the same flow and head.
Some pump configuration can allow the suction / discharge nozzles be custom made to suit the piping size to avoid the use of reducer /enlarger. Provided it does not affect the pump performance.

 

[TenPenny]

I am far from a pump expert, but I thought generally the discharged suction connection was one size larger than the line to reduce the velocity of the fluid through the pump. Is that not the case?

It's physically impossible for a change in line size to make any difference to the velocity of the fluid through the pump, if the pump and flow rate stay the same.

 

[25362]

Pump expert's considerations concerning factors that may affect NPSH are when connecting pipe and pump flanges:

[•] misalignment between the suction nozzle and the suction pipe,
[•] a gasket located eccentrically in relation to the bore of the suction flange,
[•] or when the gasket projects into the suction line by being too small; to avoid such a situation the gasket bore should be at least 1/4 in. larger than the ID of the suction pipe.

 

[cvg]

typically what I would prefer to see if at all possible is a straight length of pipe of the same size as the suction nozzle attached to the pump. reducers, elbows or other fittings which tend to increase headloss and disturb the flowlines are not desirable. if they are needed, they should generally be located some distance away from the pump if possible.

 

[Ripz]

Turns out i was wrong...


"Rules of Thumb and Myths?
The suction line size should always be one size larger than the pump suction connection size.
While this certainly insures a lower mean fluid velocity, it is contrary to the rule which promotes that pipe
fittings should be eliminated (or at less minimized) in pump suction lines. A line size larger than the
provided pump connection size necessitates the incorporation of a reducer at some juncture. Maybe a
better rule of thumb would be that the suction line size should never be smaller that the pump suction
connection size."

Link

 

[1gibson]

Never speak in absolutes.