K&N Engineering Airflow Testing Protocol
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.
| Differential Pressure Set | Range Set | CFM Reading |
| 1.5" H2O | 1 | 0 or 0% leakage (Leak Check – Plug Holes) |
| 25" H2O | 6 | 240 ± 2 |
| 50" H2O | 7 | 340 ± 5 |
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.
