Page 46 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

Installation, Maintenance, and Repair of Horizontal Pumps 31

Table 1-2
Required Diametral Clearances-Process Pumps Wear Rlngs’
Diametral Clearance
Wear Ring Diameter Under 500°F Over 500°F
3112 in. through 5 in. ,016 .018
5 in. through 6 in. .017 .019
6 in. through 7 in. .018 ,020
7 in. throueh 8 in. .019 .02
1
8 in. through 9 in. .020 .022
9 in. through 10 in. .02 1 .023
10 in. through 11 in. .022 .024
11 in. and over ,023 .025
* An additional diametral clearance of. 005 in. is provided ifboth wear rings are made of
austenitic stainless steel, Monel or other materials with high galling tendencies.

Casing and impeller wear rings are provided at both sides of the impel-
ler on API-type pumps. These rings allow a small clearance to be main-
tained between the rotating impeller and stationary casing rings. For
proper hydraulic performance these clearances should approximate the
experience values indicated in Table 1-2. Rings should be replaced when
clearances have increased to a point where hydraulic requirements cannot
be met or where inefficient operation would prove wasteful. For API val-
ues refer to Table 1-3.
Why do wear ring clearances deserve our attention? The following sec-
tion will provide the answer.

Keep Pumps Operatlno Efficiently* *

In centrifugal pumps, it is essential to pump operability and hydraulic
performance that excessive internal leakage (or recirculation) be pre-
vented. This is accomplished by establishing and maintaining close run-
ning clearances been stationary and rotating wear rings which restrict
fluid flow to seal between the inlet and outlet of each impeller and be-
tween stationary and rotating interstage bushings. These bushings effect
sealing between the stages of a multistage pump. Certain types of pumps
contain hydraulic thrust balancing devices, another source of internal
pump leakage.

** From “Keep Pumps Operating Efficiently,” by J. Lightle and J. Hohman, Dresser
Industries, Pacific Pump Division, in Hydrocarbon Processing, Sept. 1979. By per-
mission of Dresser Industries, Pacific Pump Division.