37-1-615 Page 18
TYPE OF SERVICE – The blower can be operated in either pressure or vacuum service.
Pressure – Never operate the blower above the maximum pressure shown in FIGURE 3-1. Excessive
pressure may cause overheating and blower failure, it is therefore most important to have an accurate
pressure gauge in the discharge line as close to the blower discharge as possible. Reduced speeds have
a direct bearing on allowable pressure (FIGURE 3-6). A bypass valve to bleed air from the discharge to
atmosphere (FIGURE 2-2) may be used to control the pressure. NEVER reduce the blower speed to
maintain a certain pressure before it is determined if the reduced speed is adequate for that pressure. An
accurate pressure gauge must be maintained.
Vacuum – The blower may be operated either in dry vacuum or wet vacuum service. Do not operate the
blower above the maximum vacuums shown in FIGURE 3-1, or below the minimum speed shown in
FIGURE 3-6. All vacuum ratings are based on standard atmospheric discharge. An accurate vacuum
gauge and vacuum relief valve must be used as close to the blower inlet as possible.
Wet vacuum service employs a suitable liquid, normally water, injected into the system near the blower
inlet to control temperature rise and increase the degree of vacuum developed. The liquid used MUST
BE clean and free of foreign matter, chemical contaminants and hardness, which may cause corrosion,
deposits, or damage in the rotor chamber. See FIGURE 3-4, for typical installation, and FIGURE 3-2,
for water quality requirements. If the proposed water supply is questionable, or does not meet the water
specification, a reputable water treatment service company should be contacted. They can recommend
treatment and equipment to satisfy this specification.
pH Range at 25° C....................................................... 6.5 – 8.0
Conductivity at 25°C (MICROMHO/cm) ........................ Less than 250
Total hardness as CaCo
3
(ppm) ................................... Less than 100
Total Alkalinity as CaCo
3
(ppm).................................... Less than 70
Chloride ion; CI
-
(ppm) ................................................. Less than 30
Sulfate ion SO
4
–2
(ppm)............................................... Less than 50
Total iron; Fe (ppm) ..................................................... Less than 0.3
Silica; SiO
2
(ppm) ........................................................ Less than 20
Sulfide ion S
-2
(ppm) .................................................... 0
Ammonium ion; NH
4
+ (ppm) ........................................ 0
FIGURE 3-2 – WATER QUALITY REQUIREMENTS
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