Pumps suction and discharge lines

[sridhar1312]

We normally size the pipes and isolation valves strainer or suction strainer cum flow straightener from suction of the pump to the suction header as the same size of suction size in the pump. Similarly the discharge line up to header with isolation valve and non return valve is same size as the pump discharge.

The headers are designed for the flow required by number of operating pumps.Similarly in case of multiple chillers the cooling water and Chilled water up to respective headers are same size as provided in the chiller and condenser and the header is designed for the working chillers 100% capacity.

Please let me know whether the above piping is correct practice.

 

[BigInch]

That's a great place to start the piping design. Diameter changes near the pump on either suction or discharge are usually hydrauically undesireable and often don't fit into the space available anyway. At times a smaller diameter might be OK, but that would be unusual. A larger diameter (esp. suction line) may be needed if distance is long, or a reciprocating pump is involved. Pay attention to the specific requirements of each type of equipment installed in the system. If they are sensitive to fluid velocities, take more care than usual with diameter changes.

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"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

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[pennpiper]

sridhar1312,
1. You did not state what type of pumps you are talking about so you can only expect general recommendations based on the general subject of "Pumps".

2. If you are able to visit a job site or facility (Pipeline, Refinery, Chemical Plant, etc.) you will see examples of what is the prevailing practice for that industry.

3. From my experience, 99% of the "Pumps" that I have worked on during the engineering and design phase of projects or actually seen in an existing plant has been as follows:
a) The pump suction piping from the source to just before the suction nozzle has always been one (or more) sizes larger than the pump suction nozzle.
b) The pump discharge piping from just after the pump discharge nozzle to the next piece of equipment has always been one (or more) sizes larger than the pump discharge nozzle.

 

[sridhar1312]

The pumps we re talking about is the Centrifugal Back Pull out pumps for chilled water and cooling water application.

Suction of the pump over sizing is understandable for ensuring positive suction to pumps.
Discharge length is hardly 2 or 3 meters and in this line isolation valve and non return valve takes the some place before it gets connected to the header.

When the chiller inlet /outlet to respective headers is it necessary to oversize as it will require bigger valve and handling will be difficult.

 

[Artisi]

There is no problem with having the discharge pipe and valves etc the same size as the pump discharge, especially if you have limited space available.

 

[MJCronin]

sidhar.....

As a "general rule of thumb" your approach seems reasonable.

The criteria most often used for piping line sizing is establishing an average velocity. If the velocity is in reasonable limits for the type of system AND the media conveyed, then it is a properly designed and economic system.

The "Piping Handbook" and other resources can give you target velocity ranges for your systems.

As I recall (and you should check this), chilled water circulation systems should be around ~ 7-12 fps; pump suctions ~ 3-6 fps. (Again, verify these ranges)

Pennpiper is correct for process plant liquid transfer applications; circulation systems are usually different

My opinion only

-MJC

 

[sridhar1312]

Respected MJC
Thanks for the valuable input.Yes we always size pipes limited to 7 fps for the cooling water and chilled water.