In a centrifugal pump, Why is the suction line diameter usually larger than the discharge line diameter?

1. To Reduce Friction Losses in Suction

a.  A larger suction pipe means slower fluid velocity.

Lower velocity = less friction loss in the pipe.

b. This helps maintain higher pressure at the pump suction.

Less friction = higher NPSHa (Net Positive Suction Head Available), which helps prevent cavitation.

2. To Maintain NPSHa Above NPSHr

a. Cavitation occurs if pressure at the suction drops below vapor pressure.

b. A large diameter reduces pressure drop, helping to keep suction pressure above vapor pressure.

c. This is especially critical in high-flow or hot fluid systems.

3. Discharge Side Can Handle Higher Pressure

a. On the discharge side, the fluid is already pressurized by the pump.

b. Higher pressure = smaller pipe can be used, and the fluid can still flow efficiently.

c. Slightly higher velocity on discharge is acceptable (and sometimes even desirable)

Shaft Alignment

Types of Shaft Alignment:

•  Laser Alignment
•  Dial Gauge Alignment
•  Scale Alignment

How alignment is carried out

Shims are placed in the output shaft after checking axial float. The shaft is firmly fixed. Intermediate shaft is then assembled. Backlash is checked and kept at 0.3 mm. It is adjusted by adding or removing shims. Finally the same is done for the impact shaft as well.

 

5 Leak Paths in a Mechanical Seal

5 Leak Paths in a Mechanical Seal

4 O-Rings + 1 Sealing between faces

•       Stuffing Box and Gland

•       Gland and Mating Ring

•       Rotating Part(Seal Ring) & Sleeve

•       Between Faces

•       Shaft & Sleeve

Seal Selection Parameters

The Following are the Seal Selection Parameters:

•       Media

•       Specific Gravity

–      Balanced Seal > 10 Kg

–      Unbalanced Seal < 10 Kg

•       Viscosity at Pumping Temp

•       Boiling Point and Freezing Point

•       State of Media

–      Clear / Dirty

–      Abrassive or Non Abbrasive

–      % of slurry (2-3%: Single Spring; Upto 10%: Bellows, >10%: back to back or single seal with plan 32)

–      Size of particles

–      Toxicity

–      Hazardous

–      Crystallizing (NaOH, CO3, Sea Water)

–      Any other chemical property

Types of Rod Packing - Radial & Tangent, Double Tangent, Tangent & Backup, Pressure Breaker, Single loaded tangent, Radial Tangent & Backup