Page 126 - HVAC Pump Handbook

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Physical Description of HVAC Pumps

Physical Description of HVAC Pumps 123

are bronze, while the pump shaft is either carbon steel or stainless
steel.
Other materials such as cast steel, stainless steel, and ductile iron
are found in HVAC applications where specific conditions require
their use. Some manufacturers of small pumps are now using stain-
less steel fabrications for impellers because they have found them to
be less expensive than bronze castings. Stainless steel shafts are used
by some pump manufacturers when mechanical seals are furnished
without any sleeves under them.
Higher-temperature operations above 250°F, such as medium- and
high-temperature water, will require ductile iron, cast steel, or fabri-
cated steel casings to withstand the system temperatures and pres-
sures (see Chap. 21). The working pressures and temperatures of
standard cast iron casings are always rated by the pump manufacturer.
They will provide a pressure-temperature chart similar to Table 5.2 for
a specific class of pumps and will state whether the pump nozzles are
furnished with 125- or 250-lb flanges. In the case of Table 5.2, the var-
ious letters from A to F are for different sizes of nozzles with different
ratings for each. Some of the higher ratings are for ductile iron cas-
ings. It is very important, even on a small, low-pressure project, that
the design engineer check the pressure-temperature ratings of the
pumps. It is wise to have a rating chart similar to Table 5.2 in the job
file for each application.

5.6.3 Mechanical seals or packing?
Most HVAC pumps today are equipped with mechanical seals. Many
different types of mechanical seals are offered by a number of manufac-
turers. The books listed in the Bibliography at the end of this chapter

TABLE 5.2 Typical Pressure-Temperature Limitations for HVAC
Centrifugal Pumps (Pressure in psig)
Casing and nozzle
designation 0–150°F 175°F 200°F 250°F
A 510 487 467 426
B 450 430 412 375
L 425 406 390 360
K 400 384 367 336
J 350 336 325 300
C 300 290 280 270
H 275 265 255 240
D 250 240 232 215
E 175 170 164 150
F 150 143 137 125
NOTE: The temperature limitation for all these casings and nozzles is 250°F.

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