CPM Bearings, Seals, and Shaft Couplings 2

Question 1

A mechanical seal in a centrifugal pump creates its primary seal between which two components?

Accepted Answer

A rotating seal face and a stationary seat

Answer

A mechanical seal prevents leakage through two lapped, highly polished mating faces — one rotating with the shaft and one stationary in the housing.

Question 2

Compared to compression packing, the primary operational advantage of a mechanical seal is:

Accepted Answer

Near-zero leakage during normal operation

Answer

Mechanical seals are engineered to produce virtually no leakage, whereas packing requires a controlled drip rate for lubrication and cooling of the packing rings.

Question 3

A radial lip seal (rotary shaft seal) should be installed with the sealing lip oriented:

Accepted Answer

Toward the fluid being retained

Answer

The garter spring and lip face the fluid side so that fluid pressure assists the lip in maintaining contact with the shaft, improving the seal.

Question 4

When replacing compression packing in a pump stuffing box, adjacent packing rings should be staggered by:

Accepted Answer

90° so no two ring joints are aligned

Answer

Staggering each ring 90° from the previous ensures no two ring joints align, eliminating a straight leakage path through the packing stack.

Question 5

What is the purpose of a lantern ring installed within a packed stuffing box?

Accepted Answer

To distribute flush fluid or lubricant evenly around the shaft circumference

Answer

A lantern ring is a hollow spacer with radial ports that routes seal flush water or lubricant uniformly around the shaft inside the stuffing box.

CPM - Certified Plant Mechanic Practice Test

CPM - Certified Plant Mechanic Practice Test

CPM Bearings, Seals, and Shaft Couplings 2