Custom Search
|
|
|
||
 (4) Check shaft and shaft sleeves for scoring, corrosion, or wear at
seals. S e e if shaft is straight. Check deflection by turning shaft between
lathe centers; maximum permissible runout should be from 0.003 inch to 0.006
inch, depending on pump speed. (The lower the speed, the larger the
p e r m i s s i b l e runout of the shaft.)
( 5 ) Check impellers for corrosion, erosion, or excessive wear.
Remove foreign matter in the impellers.
(6) Measure bearings for wear. I f no specific information is
a v a i l a b l e , allow 0.002-inch clearance per Inch or fraction thereof of shaft
j o u r n a l diameter, plus 0.001 inch. For thrust bearings of the sleeve and
collar type the maximum desirable axial float should be 0.016 inch.
( 7 ) Check condition of foot valves and check valves. Check valve
operation is particularly important as it protects the pump from water hammer
when the pump stops.
( 8 ) Inspect and clean suction and discharge strainers.
( 9 ) Calibrate pressure gauges, thermometers, and flowmeters. Check
to see that any breakdown or restricting orifices, which may be used for
r e c i r c u l a t i o n or venting, are clean and unobstructed.
Repai r or replace defective parts following yearly
5.3 Maintenance.
inspection.
Replace wearing rings when they are worn to twice
(a) Wearing Rings
t h e original clearance, or if the leakage reduces the capacity, head, and
e f f i c i e n c y of the unit.
( b ) Gland Packing. R e p l a c e the entire packing of the stuffing boxes;
"never add a ring or two to the existing packing. When repacking a stuffing
b o x furnished with a liquid seal, remove the seal cage (lantern ring) to take
o u t the packing behind it. Count the number of rings before and after the
s e a l cage so that it can be replaced exactly in its previous position. The
water-seal passage must line up with the seal cage. B e f o r e repacking, inspect
the shaft and shaft sleeve for scratches. A scratch where the shaft contacts
t h e packing will quickly ruin the packing. Use only packing material of the
type recommended by the pump manufacturer for the intended service. Usually,
pumps intended for general service use a high grade of soft, square, asbestos
p a c k i n g , impregnated with oil and graphite. Metallic packings are often
furnished for pumps designed for high temperature boiler feed service.
Hardened steel shaft sleeves should be furnished when using metallic packing.
If bronze sleeves are furnished, use a soft grade packing. When repacking,
cut each ring to the proper length so that the ends come together but do not
overlap. P l a c e succeeding rings in the stuffing box with joints staggered
about 90. P l a c e one ring in the stuffing box at a time; then tamp it with a
m e t a l ring or suitable tool until seated firmly before putting in the next
r i n g . A f t e r the correct number of rings are in place, set the gland to hold
the packing. D o not press the packing too tight; this may result in burning
t h e packing and cutting the shaft or shaft sleeve. The stuffing box is not
p a c k e d right if packing friction prevents turning the rotor by hand. However,
if a new pump packed with metallic packing has been stored for a great length
4-26
|
 
|
|
|
||
