Read up this short note on Pumps

PUMPS

Suction Piping for Horizontal Pumps

Line Size

Suction piping is usually one or two line sizes larger than the pump suction nozzle size. Suction piping more than two sizes larger should be queried with Process Department.
Suction Nozzle Orientation
Centrifugal pumps are supplied with suction nozzles on the end of pump casing, axially in line with impeller shaft, also on top or side of pump casing. Usually pumps are specified with end or top suction for general services. Side suction pumps, with side discharge are frequently selected for large water duty. Also side suction - side discharge pumps can be obtained in multi-stage form for higher pressure differentials. These pumps tend to become very long, so if plot space is tight, consideration should be given to purchasing the pump in vertical form with a sump at grade. See below figures.

Flexibility of Suction Lines

Consistent with good piping practice, pump suction lines should be as short as possible, but with enough flexibility to absorb any pipe movement caused by temperature differentials and to maintain pump nozzle loads to within those permitted by pump vendor. For further details refer to section on piping flexibility.
Suction Line Fittings
Due to suction line being larger than the suction nozzles, reducers are required in the line. Reducers should be as close as possible to nozzle. Eccentric reducers will be used with the flat on top for horizontal pumps. See below figures. For pumps with suction and discharge nozzles on top of casing, care must be taken to ensure that the flats on eccentric reducers are orientated so that suction and discharge lines do not foul each other. See below figures.

Temporary Start up Strainers

All pumps must have a temporary start up strainer in the suction line to prevent any pipe debris damaging the pump. Strainers will be located between pump suction block valve and pump. Strainers are available in the following styles : flat, basket, conical and bath or “tee” type.
For basket and conical types a removable spool piece must be provided downstream of suction block valve, which must not interfere with line supports. Both types have the advantage that the piping is left undisturbed and strainer element can be removed simply by removing the blind flange on the tee, thus leaving the piping and supports undisturbed. See below figures
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