Frequently asked questions:
Question 1: How can I test my infiltrometer for leaks?
Separate the disc from the infiltrometer tower.
Close the tubing clamp on the bubble tower and close the bottom outlet of the water tower with a stopper.
Inflate the infiltrometer to about 60 to 100 cm water pressure (60 mbar to 100 mbar).
Hold the complete unit under water and check for leaks.
Next, check the infiltrometer disc for leaks
(Note: Before installing the nylon mesh screen material, make sure the disc is free from small particles. These may cause leaks. Install a new mesh screen membrane if necessary).
Connect 1/4" tygon tube (60 cm long) to the outlet in the center of the disc.
Immerse the disc and tube in a dishpan full of water. The tube should be completely full of water. Make sure there is no air under the membrane or in the tube.
Close the open end of the tube with a tubing clamp or with a small stopper.
Remove the disc with attached tube from dishpan.
Now turn the disc, so the screen is facing up.
Position the tube so the end of the tube is at the same level as the top of the screen. Open the tube and slowly lower the end of the tube. Watch if air bubbles appear below the screen. Air bubbles should start appearing when the open end of the tube is 25-30 cm below the level of the screen. This is the bubbling pressure of the nylon membrane.
If air bubbles appear when the tubing outlet is less than 20 to 25 cm below the screen level, then there is a leak in the screen. Replace the screen, making sure that no loose particles are lodged between the screen and the screen support or between the o-ring and the screen.
Question 2: Should I calibrate my tension infiltrometer?
You can, and probably should calibrate it. However, all SMS tension infiltrometers are made using the same diameter tubing, and thus the calibration for all tension infiltrometers should be approximately the same. To start with, you can set the tube in the bubble tower such that its outlet is 4.0 cm below the desired tension. For example, if a tension of 5 cm is desired at the level of the membrane, move the tube in the bubble tower up or down till its outlet is at 9.0 cm below the water level in the bubble tower. After you have had some experience with the tension infiltrometer, you may want to check itscalibration.
Question 3: What is the difference between the 8-cm model and the 20-cm model?
The 8-cm model is smaller and uses less water. It can also be used in a smaller space. However, the disc surface is considerably smaller than the disc surface of the 20-cm model, causing greater variance in the measurements. The 8-cm model is good for measurements between crop rows, and is also very good for teaching purposes. This model can further be used to control the tension on top of soil columns in thlaboratory.
Question 4: Can I replace the membrane in thfield??
Yes this can be done quite easily. Remove the old membrane after loosening the holding ring. Wet the new membrane (this makes it much easier to install), place the new membrane over the disc, replace the holding ring, tighten the screw, and you are done.
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