Technical data

Tapping the side of the separatory funnel may help to
remove the high-density particles. Do not allow fluid
level to get too low, because it might allow some
floating media to be deposited with the high-density
contaminants. Additional fluid may be added to separa-
tory funnel taking care not to agitate mixture. If agita-
tion occurs, allow 10 minutes for suspended dust par-
ticles to float/settle prior to continuation. To separate all
of the high-density particles, the process has to be
repeated until no particles will separate out of the plastic
media. One attempt will not extract them all.
f. Place the filter and filtrate in a vented, dust free location
(preferably, a laboratory hood) to dry for one hour.
Weigh the filter paper and filtrate to 0.001 gm precision.
Allow the filter paper to dry an additional 30 minutes
and reweigh. If there is a change greater than 0.001 gm,
continue to dry the sample, checking the weight every
30 minutes until the weight between intervals does not
change. Obtain the tare weight of a watch glass, or on an
electronic balance so equipped, and reset the balance to
0 with the watch glass on the pan. Carefully remove the
filtrate from the filter paper onto the watch glass by
tapping. Unfold the filter paper and remove the remain-
ing particles with a hard instrument, such as a metal
spatula, until no visible sign of particles remain. Do not
use a brush. Fine particles or dust may have impregnated
the filter paper. This residue is not a major concern and
may be disregarded because fine particles (less than 80
mesh, US Standard Sieve) are not damaging to aircraft
materials or structure. Depending upon the balance
used, weigh or calculate the weight of the dense
particles to 0.001 gm precision and record as Weight #3.
(Gross weight minus weight of watch glass). After
weighing use a magnet to determine if any steel/ferrous
material is in the dense particles. This information may
help in determining the source of the contamination and
facilitate process troubleshooting. However, the 0.02%
dense particle contamination level in Paragraph
2.11.12.3 (i) is the basis for acceptance or rejection of
the media regardless of the contamination composition.
g. Filter the used test fluid mixture through a funnel with
clean filter paper, and retain for reuse. Store in a
separate, small-neck, tightly closed and properly labeled
container. Recheck specific gravity with a hydrometer to
assure it is in the proper range prior to reuse.
h. Calculations: Gross weight of media and 500 ml beaker
(Weight #1) minus tare weight of 500 ml beaker (Weight
#2) equals net weight of media, and weight #3 is the
dense particle weight. The dense particle weight divided
by the media weight equals the weight fraction of dense
particles in the sample. Multiply the weight fraction by
100 to find the weight percent of dense particles in the
sample.
Dense Particles Wt
× 100 = Percent
Media Weight
i. Sand, concrete, and glass particles tend to cause pitting
and the most fatigue life degradation while steel/ferrous
particles will pit and embed in softer aluminum and
magnesium substrates. The high density particle con-
taminant level shall not exceed 0.02% for all used media
employed in aerospace equipment stripping operations.
For non-aerospace equipment (SE, vehicles, etc.) strip-
ping operations, the high density particle contamination
level shall not exceed 2.0% for used media.
2.12 MPW REMOVAL METHOD.
This removal method requires the use of a medium-pressure
water and bicarbonate of soda injection system with control,
hoses, and handheld nozzles of various configurations. The
injection system shall consist of a positive feed control
system, such as an auger/computer controlled system. This
MPW removal system, with or without abrasives is an
excellent method for finish system removal, but can cause
severe damage to structure and injury to personnel, if not
done properly. MPW paint removal is authorized at depot and
field-level operations subject to SPD approval of facilities,
equipment, personnel training, and technical data. These
instructions are not intended to be all inclusive, but are
general, necessary guidelines to be used in conjunction with
additional instructions in applicable system-peculiar aircraft
or equipment manuals and a definitive process order. All
MPW removal operations shall conform to the following
requirements:
NOTE
Only the equipment and supplies listed below
have been approved for Air Force use. The
medium-pressure-water equipment are the E25M
Electric Unit, NSN 4940-01-413-5627/4940-01-
395-9471; the D44 Diesel Unit, NSN 4940-01-
411-9826/4920-01-413-5629, and the B-25 Elec-
tric Unit (least expensive basic unit), NSN 4940-
01-451-0020, all without rotating gun. For a
portable unit, a trailer NSN 4940-01-413-5602
can be used. It is recommended that the repair kit
Model 900-005, NSN 4940-01-411-9829 be
bought with the blast equipment. The bicarbonate
of soda blasting media is available in 40-pound
bags under NSN 5350-01-414-1894.
2.12.1 Preparation. Proceed as follows.
a. Prior to masking for MPW paint removal, the aircraft
and other equipment shall be defueled and purged. In
addition, if deemed necessary, the aircraft or extremely
contaminated areas on the aircraft shall be washed in
accordance with TO 1-1-691.
b. Before starting the MPW paint removal operations, the
aircraft, equipment, or component shall be properly
masked and sealed to prevent water or bicarbonate of
soda blast media from penetrating into interior areas and
TO 1-1-8
2-25