K&N
Engineering performs all airflow testing on a SuperFlow
Corporation SF-1020 flow bench. The SF-1020 is a
computerized flow bench capable of measuring airflow rates up to
1020 cubic feet per minute (cfm) at test pressures of up to 65
inches of water.
K&N has developed the following procedures for measuring airflow
and pressure differential (restriction) of the various size and
shaped filter elements that we manufacture. These procedures
must be followed to insure a consistent comparison of air flows
between filters that are of differing material or manufacture.
Daily Calibration & Leak Check
The calibration check is a three step procedure to verify that
the measurement of the flow bench is accurate and will be
performed daily before the bench is used. To complete the
SF-1020 calibration check, a test orifice plate supplied by the
manufacturer is used. This plate has one 1.875” and one .312”
hole in it.
Operate the flow bench with the test orifice plate in place and
adjust the pressure
differential control setting and intake flow range to each of
the values below. The
measured flow should match the corresponding flow specified by
the manufacturer with
the test orifice in place. Perform the leak check first. To
perform a leak check, use the
rubber stoppers to plug the holes in the orifice plate. If any
of the readings are out of
tolerance the problem must be corrected before testing. This
daily check will be
documented in a log. |
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Filter Element Test Procedures
When testing filters, it is imperative to select the proper test fixture or
adapter that is compatible to the filter shape and size. It may be necessary to
fabricate or source the fixture for new element configurations. Additional steps
may be necessary to insure that the element is fully sealed to the test fixture
and no air leaks exist around the base or any openings (e.g. holes for mounting
or fittings).
It is important to flow the filter in the correct orientation as to the
direction of designed air flow. This is the direction of air moving from the
dirty side to the clean side of the element.
To determine the appropriate flow range for the filter under test, a preliminary
flow test must be performed. Select intake flow range #10 (1000 cfm ). Start the
flow bench motor and allow the test pressure to stabilize at 1.5” H2O. Observe
the cfm reading on the digital readout. Shut off the flow bench motor and select
the intake flow range that is one step higher than the preliminary test reading.
Round Filter Test Procedure
When testing round air filters, entry base plates manufactured with a .250”
entry radius will be installed on the air intake duct of the SF-1020. A base
plate will be selected with an entry diameter closest to the inside diameter of
the filter. The filter to be tested is centered over the hole in the entry
plate. A corresponding diameter, 0.250” thick, aluminum top plate is used to
seal the top of the round air filter.
The top plates have a ~.125” hole in the center to incorporate a Pitot/static pressure tube to read the static pressure inside the
filter element. It is important to note that the static pressure is measured
through the holes in the tube that are around the circumference about an inch
from the tip and the static pressure tap from the SF1020 is connected to the
static pressure tap on the side of the Pitot tube. The Pitot tube tap on the end
of Pitot tube is to be capped. Care must be taken to avoid clogging any of
the holes in the Pitot tube as this will adversely affect the accuracy of the
device.
The Pitot tube is inserted into the hole of the top plate to a depth of
approximately 1” below the top of the filter element and the area around it
sealed with a bit of clay. To measure the flow, set the SF1020 Bench to a fixed
1.5” H2O differential pressure and select the appropriate intake flow range that
was derived from the preliminary test above. Turn on the bench blower fan, allow
the readings to stabilize. The operator can then freeze the digital display
reading at exactly 1.50” H2O and record the cfm reading.
Flat Panel Test Procedure
To test flat panel air filters, a panel filter test fixture has been fabricated.
The plenum of the fixture measures 17” long x 10.5” wide x 5.75” deep. The
bottom of the box has a 9” diameter hole with a 0.500” entry radius. The panel
filter air box will be installed on the air intake duct of the SF-1020. A Pitot/static tube is positioned in the lower corner of the plenum. The top of
the box features 4 adjustable slides to accommodate various size panel filters.
The panel air filter to be tested is to be placed on in the air box and the
slides adjusted to provide a positive seal on all 4 sides. For panel filters
that are not rectangular or are multi sided, care must be taken to seal the
entire filter perimeter to the test fixture so there are no leaks. Connect the
static pressure tap of the SF-1020 to the static pressure tap on the side of the
Pitot tube. The Pitot tube tap on the end of Pitot tube is to be
capped.
To measure the flow, set the SF1020 Bench to a fixed 1.5” H2O differential
pressure and select the appropriate intake flow range that was derived from the
preliminary test above. Turn on the bench blower fan, allow the readings to
stabilize. The operator can then freeze the digital display reading at exactly
1.50” H2O and record the cfm reading.
Conical and Universal Clamp-on Test Procedure
Accurate air flow and pressure drop of conical and universal clamp on
air filters, in which the base of the filter is molded into the filter
assembly and cannot be removed, is difficult to measure because the
clamp on base is usually the most restrictive part in this type of
filter.
Therefore, K&N has chosen to measure the static pressure
of these types of filters by inserting a static pressure Pitot tube into
the central portion of the filter base where the filter clamps to the
tube or throttle body.
When testing a conical or universal
clamp-on filter, various small base plate adapters manufactured with 2”
to 6” diameter tubes will be installed on the air intake duct of the
SF-1020. A base plate adapter will be selected with an entry diameter
that matches the diameter of the filter flange.
In preparation
for testing, a Pitot of the proper length will be inserted through the
adapter tube and adjusted so the static pressure ports are located at
the flange of the filter as near to the center as possible. The filter
is then installed on the adapter and the neck or clamping surface, if
one exists, will be tightly clamped to the adapter base. It may be
necessary to use a bit of clay or tape to seal irregularities to ensure
no leakage.
It is important to note that the static pressure is
measured through the holes in the tube that are around the circumference
about an inch from the tip and the static pressure tap from the SF1020
is connected to the static pressure tap on the side of the Pitot tube.
The Pitot tube tap on the end of Pitot tube, if so equipped, is to be
capped. Care must be taken to avoid clogging any of the holes in the
Pitot tube as this will adversely affect the accuracy of the device.
To measure the flow, set the SF1020 Bench to a fixed 1.5”H2O
differential pressure and select the appropriate intake flow range that
was derived from the preliminary test above. Turn on the bench blower
fan, allow the readings to stabilize. The operator can then freeze the
digital display reading at exactly 1.50” H2O and record the cfm reading.
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