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8.8
Any output flow greater than the stated maximum output flow for any particular
model pure air generator produces air with purity worse than specifications. A
nomograph is supplied (Figure 17) indicating output flow versus rotameter reading
at STP.
8.9
The operator must realize that once other equipment is connected to the pure air
generator and output flow is controlled at the other equipment, the rotameter will
then be pressurized and will indicate less flow than is actually being delivered.
8.10
Relevant direct rotameter readings can be made only without any equipment
connected to the output of the rotameter. This is because all rotameter calibrations
are performed at ambient pressure (in actuality @ STP). Once equipment is
connected to the PURE AIR fitting on the rear of the pure air generator the
rotameter now becomes pressurized and will no longer be direct reading.
8.11
The operator can quickly calculate actual flow even though the rotameter is
pressurized. To do so, note the output pressure and the rotameter reading. If the
output pressure is set at 15-psig, then the rotameter is at two atmospheres and
indicated rotameter reading will be one half the actual flow. In this instance, the
operator multiplies the indicated reading by two to find the actual flow.
8.12
If the output pressure is set at 30-psig and the rotameter indicates 50-mm, as an
example, then full flow is being taken from the unit since the rotameter is now two
atmospheres above ambient. This same rule of thumb will apply at other pressure
settings; i.e., at45-psig the rotameter reading should be no greater than 25% of full
scale.
17
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