Pump Reducer & Expander

Don't you mean eccentric & consentric?

it is not about the type of reducer to be used but you can assume its concentric type.

any idea?

Do you mean ''expander'' and ''reducer'' in the direction of flow? This is unusual, as more often pump connection sizes are equal or less than appropriate pipe diameters, requiring tapers the other way round.

But if you calculate correctly the pipe losses, including the tapers, you can plot a system curve to add to pump curve and find the flow. Might need to watch NPSH available.

Cheers.......Codey

Suction side:

Say you have a 8" pump inlet and want to use a 6" suction pipe. Possible if you have a positive or very low suction hight and the distance is short and your NPSHA is within limits. I would go for the bigger pipe.

Delivery side

It is also Possible to use a pipe smaller than the outlet. The best practice would be determined by economics. The total cost (smaller capital cost and higher running cost) of the smaller pipe must be compared to the total cost (high capital cost + smaller running cost) of the bigger pipe. Let your wallet be the judge.

Thanks for your inputs

How the smaller pipe would have higher running cost? do you mean the reduction in pump impeller life due to low NPSH?

The same quantity of water through the same length will produce more friction losses in the smaller pipe, therefore more energy required.

"Power Engineer"

We do not know what your education, training or experience is so it is difficult to comment on your question. From the wording of your question I am reasonably sure you are not a piper.

With that in mind I will offer the following.

1. There is no such thing as a piping fitting called "expander". You cannot order a fitting called an expander (or increaser) from a pipe fitting vendor. There is a fitting that is used when the line size changes and that fitting is called a "reducer". This fitting is called a "reducer" no matter whether the line is changing from a larger size to a smaller size or the other way around. The proper terminology used is always larger size by smaller size (e.g.: 8"x 6", etc.).

The following answers are from questions from others on other forums)

2. I will not try to give you a technical answer for this but I will try to give you an understanding of the situation. First you do not change the pump nozzle to match the line size just to save the cost of a reducer. To change the size if the nozzle part of the pump case would be very much more expensive than the reducer.

So why the different size pump nozzle in the first place? Try to look at it this way. It is a matter of "Supply and Demand". The "Demand" relates to the pump. It is designed to move a certain amount of a specific fluid having specific design conditions. The pump is a specific size but it has that motor (or Turbine) driver providing the power that moves the fluid along.

To make the pump work properly you must guarantee the proper conditions at the inlet to the pump. This is called NPSH (Net Positive Suction Head). The suction line is included in the physical system that is the "Supply" part of this matter. The suction line is normally only a gravity driven conduit that must pass the same amount of fluid as the motor driven pump. To do this you must have a larger suction line than the pump nozzle. If you have a larger suction line then you have a "Supply" that meets the "Demand".

Like I said, this is not a highly technical answer but I hope it helps. So go ahead and add the reducer in the pump suction. But remember, in pump suction lines, install the eccentric reducer with the flat side on top.

3.The process engineer determines what line size is required for all lines to perform the function of the process. This is true for both the suction and the discharge lines for pumps. The Pump Engineer specifies and purchases a pump that will perform the function of the process. Due to the nature of the pump, the pump suction and discharge nozzles almost always (95% of the time) turn out to be one or more sizes smaller than the connecting line sizes. You may ask why they don't buy a bigger pump, or at least a pump with a bigger nozzle. Well it is pure economics. The bigger pump or the pump with bigger nozzles cost extra money and probably will not perform properly or be cost effective.

So what do we have? We have a pipe line (specified by the process engineer) and a pump (specified by the pump engineer) which needs to be connected. The piping is done by a responsible, well trained, and experienced piping designer. It is the piper's job to know what to do and do it right.

I hope this helps.

''PennPiper'' appreciate your comments it shows that you are expert in piping

First let me introduce my self i am a junior mechanical engineer working in power station

With regard to your comment i have stated the term ''expander'' just to give the reader a clue that the existing pipe size is smaller than the nozzle size at suction side of the pump so my intention is to connect the small pipe to the bigger nozzle through a fitting ( give it any name)

I think that you understand it the other way which could be my mistake not to mention this clearly in OP.

Good day pipe engineer

You should also investigate the reason for a possible oversized pump. It may have occurred in an emergency situation where only a big pump was available and due to a policy of not scratching where it does not itch the pump may stay there forever.

The efficiency at the duty point may however be low and additional discharge pressure may be destroyed leaving the system to consume additional energy.

Dear Power Engine,

I. You should not use reducer in the suction pipe since

1. The required flow quantity will not be ensured, thus causing starvation leading to churning and over heating.

2. The frictional loss will be increased leading to higher pressure drop.

II. For the Delivery side reducer will call for more velocity and hence more frictional loss.

THANKS,

DHAYANANDHAN.S, INDIA.

This is an old thread.

I didn't read all the posts, but one items you need to understand, that any and fittings that's installed on the suction end or the discharge end with its a valve, a fitting such as a reducer or elbow as an example the distance there should be at least (5) five pipe diameters of the suction head and (5) five diameters of the discharge head.

Generally, <...pump[s]...> are supplied with pipe connections appropriately sized for the flows expected to be produced. Putting a <...reducer...on the discharge side...> works exactly like a partially-closed valve downstream.

Putting an <...expander...on suction side...> also works like a partially-closed valve and, in the limit, can cause cavitation to occur within the <...pump...>, which will increase its damage rate.

As a rule-of-thumb, if the average velocity of liquid in the pipe exceeds 3ms^-1 then the pipe is undersized; if it is less than 1ms^-1 then it is oversized.

It sounds as though the <...pump...> and the piping system are fundamentally incompatible with each other in this case so instead of fudging it the matter is better left to an experienced piping designer instead. Seek out design guidance before proceeding further.