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PPQ
speed indicator is used, the reading in miles per hour should be
converted to feet per minute by multiplying the miles per hour by
5,280 and dividing by 60.
Area of the fan is calculated by first measuring the radius
(R)—distance from center of fan to end of a blade. Formula for area is
¼ R2 where ¼ is equivalent to 3.1416 (22/7). The final answer should
be given in cfm. Therefore, if the radius of the blade is given in inches
and not feet, the factor 1/144 must be multiplied in to convert square
inches to square feet. The full formula would be: Feet per minute × R2
(in inches) × ¼ × 1/144 = cfm.
EXAMPLE: If average air movement is 1,600 feet for 1 minute from a fan
having a 7 inch radius (14 inch diameter), the calculations are as follows:
1,600 × 72 × 3.1416 × 1/144 = 1,700 cfm (approximate)
Velometer
The Velometer is the registered trade name of Illinois Testing
Laboratories, Inc., Chicago, Illinois, for their air speed indicators.
Readings are taken by either holding the instrument itself or jets
(probes) in front of the air stream. Velocities are rapidly determined in
units of feet per minute without timing or calculations. Units are
especially useful for measuring air flow in ducts and in front of grilles.
Auxiliary Pump
During the fumigation of large enclosures, it is necessary to take
numerous gas concentration readings from various locations
throughout the enclosure. Thus some sample leads may be over 200
feet long. The fumigant must be pumped to the sampling point before
an accurate concentration reading can be made. If the inspector must
rely on the pump provided with the gas sampler or thermal
conductivity unit to pull the fumigant, a great deal of time will be
needed between readings.
The auxiliary pump will reduce sampling time to only the reading time
since it pumps the fumigant from many areas and keeps a constant
pull. Construction of a unit is relatively simple. Petcocks capable of
accepting sample leads are tapped and soldered to a short length of
pipe. This pipe is connected to the suction side of the pump. The pipe
acts as a manifold. Opening or closing the petcocks allows the drawing
of the gas samples as required. An exhaust line of sufficient length
should be connected to the pump to ensure the fumigant is removed
from the sample area.
Equipment
Air Velocity Measuring Instruments
8-1-28 Treatment Manual 06/2004-01
PPQ
It is important that all soldering be done in such a manner as to
provide gas tight construction of the petcocks. The pump should be of
sufficient size to pull 1 cubic foot per minute through all of the leads
on the manifold. Therefore, the more leads, the higher the required
capacity of the pump. The whole unit should be mounted on a board
large enough to keep vibration to a minimum. The unit weight should
be kept down to allow easy transport.
Each sampling line is disconnected from the auxiliary pump in turn,
and the petcock closed. Line is then attached to the T/C unit or gas
detector. A reading is obtained and line reconnected to the auxiliary
pump and the petcock opened.
Open Arm Manometer
The manometer is a U-shaped tube partially filled with kerosene or
water. The tube may be of glass or transparent plastic tubing. A ruler
calibrated in millimeter (mm) divisions or carefully measured lines on
a background is used to measure the difference in level of the
kerosene in the two arms (or the level in one arm).
When a fumigant is volatilized in a chamber at atmospheric pressure,
a positive pressure is created, which may then be continuously
reduced by leakage of the air-fumigant mixture. PPQ approved
chambers must be sufficiently tight to retain the fumigant during the
exposure period. The manometer is used during the pressure-leakage
test as a measure of tightness. An opening (usually 1 inch diameter)
should be provided in the chamber for the use of a blower or other
means for the introduction of air to create a positive pressure in the
FIGURE 8-1-5: Auxiliary Pump
Equipment
Air Velocity Measuring Instruments
06/2004-01 Treatment Manual 8-1-29
PPQ
chamber. An additional opening, such as a gas sampling line opening,
must be provided for the manometer. The procedure for testing is as
follows:
◆ Close chamber as for fumigation
◆ Attach one end of the manometer to the chamber opening
◆ Use vacuum cleaner blower or similar apparatus to create
pressure of 25 mm as measured on an open-arm, kerosene or
water filled manometer
◆ Discontinue blower and close its entry
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