Permeability Tester (Analog type) NKP-V2

Quick method

The apparatus is placed on a horizontal desk. The three-way valve is turned to "Open" to introduce water so that the air chamber is floated to the mark "W". Then the valve is turned to "Measure" to introduce air so that the air chamber is lowered to a position slightly below the "0" line, and then the valve is turned to "Close" to stop air flow. An orifice, either the small one or the large one, depending on the sand grain fineness, is screwed in the rubber stopper after inserting a rubber ring for preventing air leak. The test sand is rammed using a sand rammer into a test piece cylinder of a standard shape, and the cylinder with the sand is tightly pushed in the rubber stopper. The valve is turned to "Measure" to raise air pressure in the sand cylinder. After reading the value of the pressure gauge, the valve is turned to "Close". Table.1 gives the permeability value corresponding to the pressure value thus measured.

Standard method

\[Permeability = {V \times H \over P \times A\times T}\]

• V =air volume passed through the test piece (cc) 2000cc
• P = pressure difference between the upper side and lower side of the specimen (Pa) (P = Pa ÷ 98)
• A = sectional area of the specimen (A = 19.635cm²)
• H = height of the specimen (cm) (5.0 ± 0.1cm)
• T = time necessary for the air of 2000cc to pass the specimen (min)

Testing of dry sand mold

A standard specimen (50mm in diameter and 50mm in height) is prepared with a sand rammer and is taken out with a push rod for drying. A weak specimen is taken out on a disc of 50mm diameter and sent to drying on the disc.
The specimen is dried at 105 to 115 degree C for one to two hours and taken out for cooling. After cooling, it is inserted in a dry sand permeability specimen cylinder. The valve on the cylinder is opened and air is sent from the rubber bulb to the rubber sheath in the cylinder for ensuring pressure tight support of the specimen. The cylinder is inserted into the rubber stopper, and permeability is measured in the same way as the case of the green sand.

Calibration of orifice

The air chamber should be lifted very slowly not to disturb water in the tank.
Orifice should be kept clean. The holes should not be deformed, and hence, they must be checked occasionally. Size of the holes can be checked in the following manner. Attach an orifice to the apparatus and let the air in the air chamber flow out
through the orifice without attaching a test piece cylinder. Time is measured while the air chamber sinks from the level of "0" to "2000". If the time value does not fit the standard shown below, the hole size of the orifice must be corrected.

Precautions: The orifice with the hole diameter of 1.5 mm is used for permeability above 36, and the orifice with the hole diameter of 0.5mm is used for permeability below 49.

The relation between air pressure and permeability

• Use the small orifice for medium to fine sand grains.
• Use the large orifice for medium to coarse sand grains.