Page 51 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

36 Major Process Equipment Maintenance and Repair

Table 1-3
Mlnlmum Running Clearances
Diameter of Rotating
Member at Clearance Minimum Diametral
(inches) Clearance (inches)
e2 0.010
2.000-2.499 0.011
2.500-2.999 0.012
3.000-3.499 0.014
3 SOO-4.999 0.016
5.000-5.999 0.017

ture in the impeller eye, and can introduce undesirable flow patterns in
the impeller inlet. On pump installations having marginal NPSH* avail-
able, these effects can result in noise, vibration and physical damage nor-
mally associated with cavitation.
Original design wear ring clearances can be obtained from the pump
manufacturer, and usually agree with the diametral clearances specified
by API Standard 610, Section 19. The API recommended clearances are
shown in Table 1-3 and are comparable to the experience values shown in
Thble 1-2.
The proper running clearances have been established based on operat-
ing economy consistent with good pump reliability.
Over a period of time, the design clearances will change due to wear,
corrosion or perhaps as a result of operational problems such as over-
heating, thermal shock or problems with bearings or shaft sealing sys-
tems.
The best way to maintain minimum operating and maintenance costs
resulting from increased wear part clearances is to establish a standard
practice of measuring the running clearances whenever a pump is disas-
sembled for any reason. On certain multistage pumps having thrust bal-
ancing devices, monitoring external balance leak-off flow can be used as
a means of gauging wear of internal parts. Increased balancing flows are
a direct indication of wear. In addition to measuring running clearances
during normal downtimes, wear parts should be checked for eccentricity,
out of roundness, and signs of excessive corrosion or erosion.
For best operation, obtain needed replacement parts from a reputable
source. This will ensure correct materials, proper heat treatment to main-
tain correct hardness and wear properties, and proper manufacturing tol-

* Net Positive Suction Head