20 cm survey chamber maintenance

The 20 cm survey chamber uses a series of three gaskets to seal the chamber against air leaks between the soil collar and the chamber. The first gasket is a black neoprene gasket (part number 224-07606) that is located on the bottom of the moveable part of the chamber; in most cases this gasket will not need to be replaced unless it is inadvertently damaged. The other two gaskets are located on the underside of the chamber, beneath the metal flange that envelopes the soil collar. These two gaskets, and in particular the white foam gasket, may need to be changed with some regularity.

The black rubber gasket is referred to as the soil collar gasket; four spares are included in the spares kit under part number 6581-108.

The white foam gaskets are referred to as foam seal gaskets; a package of 20 is included in the 8100-632 gasket kit, or individually under part number 6581-107.

Foam seal gasket

The foam seal gasket can become cracked or lose its shape relatively quickly, depending upon the conditions they are used in, and the pressure with which they are placed over the soil collar. Inspect the foam seal gasket before you start making measurements each day; if it appears that it might not form a tight seal against the soil collar, you should replace it.

It is not necessary to remove the soil collar gasket when replacing the foam seal gasket. The collar plates do not need to be removed from the chamber.

If you need to replace the foam seal gasket, simply pry it out with a knife or a screwdriver and discard the damaged gasket. In some cases you can simply flip the gasket over and use the reverse side before replacing.

Insert the new foam seal gasket by working the gasket with your fingers into the recessed area of the flange. It may help to work the gasket in with the inside edge first, as shown below. Press in opposite sides of the gasket to prevent stretching it. Make sure the gasket is seated all the way down into the flange, and that it lays flat without warping.

Soil collar gasket

The soil collar gasket should not need to be replaced unless it is torn. To replace the gasket, loosen the six screws on the chamber bottom plate. Remove the plate and gasket. Align the new gasket with the screw holes and reassemble.

The 6 screws on the bottom plate are captive; they need only be loosened, not completely removed.

Chamber gasket

The bottom of the soil chamber "bowl" has an attached adhesive gasket that seals the chamber against the bottom plate. This gasket has a long life, and should be replaced only if it is damaged and does not form a tight seal.

  1. Remove the four nuts from the bottom of the chamber supports, as shown below.
  2. Bend the supports out slightly to remove the bottom plate assembly.
  3. Use a knife or razor blade to remove the old gasket. Clean the rim of the chamber with alcohol if necessary to remove any adhesive residue.
  4. Remove the adhesive backing from the new gasket and install around the rim of the chamber. Trim the gasket as needed so that the ends are touching.
  5. Apply a small amount of Loctite to glue the ends together.