Piezometers

If the beeper stops working, we’ll have to fix it at the factory. The beeper could be bad or the transistor that controls the beeper could be bad.

If the light stays on, there is probably water inside the probe. You can check this by opening up the reel and disconnecting one of the wires from the board inside. If the light goes out, check the probe to see if there is water inside. Then dry it out and try to find out why it leaked.

You can contact us to order replacement parts .

Yes. Here are instructions for attaching the probe. Before you order just the replacement probe, check the graduations on your cable. Is it time to replace your cable? Also, if you lost your probe, your cable may have lost some cable with it. In that case, the depth marks will be incorrect when you attach the new probe.

Please contact us and we can help you find the required part.

Yes. Click this link to learn how to return your water level indicator to the factory.

The rule of thumb is that the grout should have a lower permeability than the surrounding soil so that water does not migrate through the grout to the intake area of your standpipe piezometer. The standard practice is to place a bentonite seal above the sand intake zone and then place grout above the seal. Any lag time between changes in pore-water pressure in the ground and changes in the water level in your standpipe is really from the volume of your standpipe and the permeability of the surrounding ground. The grout itself has little influence so long as it prevents migration of water from above. We sometimes recommend the same grout mixes that we use for vw piezometers.

There are two types of piezometers in common use today: standpipe piezometers and diaphragm piezometers (VW or pneumatic). There is no need to saturate standpipe filter tips. Water flows into them easily. VW and pneumatic piezometers do not require saturation either, but there is some air in front of the diaphragm that should be displaced, as explained below:

Diaphragm piezometers, whether VW or pneumatic, contain air between the diaphragm and the filter. For best results, you should displace this air with water. VW piezometers have a removable filter. Pull on the knurled ring to remove the filter. Fill the cavity with water and then replace the filter. Pneumatic piezometers don’t have a removable filter. In this case, you simply direct a slow stream of water into the piezometer or submerge it in a bucket of water and tap the bubbles out.

Some people install the VW piezometer with its filter end up, and our instructions for grouting-in piezometers use this technique. This generally isn’t possible with a pneumatic piezo, since tubing is so stiff. In any case, not much water will drain out of the piezometer so long as it isn’t knocked about during installation.

What happens if there is a small bubble of air? The air will slow the response of the piezo, since the air bubble must deform before it can transmit the pressure of the water. More water must flow into the piezometer to make that happen. Eventually, the air bubble reaches equilibrium and transmits the full pressure of the water. If there is plenty of water available, the slowed response is unlikely to cause much of a problem, and over time the air bubble will disappear. If the piezometer is installed in a low-permeability soil, where less water is available, this process will take longer.

High air entry filters, are generally not appropriate for standpipe or diaphragm piezometers. The high air entry filter relies on the surface tension of water in its pores to sustain a pressure difference between air and water on the filter surface. This keeps air out of the measuring system and allows measurement of matrix soil suction (negative pore-water pressure) that is present in non-saturated, cohesive soils, such as clays in embankments. The high air entry effect is operative only when the filter is saturated with water. When water drains out of the filter, the high-air entry effect disappears.

Generally speaking, only one type of piezometer, the hydraulic piezometer, is capable of maintaining saturation of the filter in non-saturated soils. Diaphragm piezometers and standpipe piezometers do not normally have this capability, and therefore should not be specified with high air entry filters. In addition, most diaphragm piezometers are not calibrated to read high negative pressures and thus, even if the filter properties were intact, would not be able to read those pressure.

A high-air entry filter can be saturated as follows: Remove the filter. Saturate it in deaired water. Replace the filter while holding the piezometer underwater. Bag the piezometer in deaired water to maintain saturation until installation.

To prepare deaired water, boil the water and apply a vacuum or use a device such as a Nold DeAerator, which combines propeller cavitation with a vacuum to deair the water rapidly.

To saturate the filter, place stoppers in the top and bottom of the filter. Place a vent tube through the stopper at the top of the filter. Immerse the filter in deaired water. Water flowing through the filter will displace the air inside the filter, which flows out the vent tube. Allow the filter to remain in the deaired water for 24 hours.

If the soil is saturated and the piezometer is saturated, there should be no problem with clogging because there is no place for the mud to go. Clogging over time implies some kind of flow, but water does not actually flow through the filter. The piezometer measures static hydraulic pressure.

The Push-In Piezometer was designed to be used in very soft soils, especially soils whose structure or hydraulic characteristics would be disturb by drilling. Normal installation procedures for the push-in piezo are to drill within 2 to 5 feet of the target zone and then push the piezometer to the required elevation. Once the push rod is removed, the soil usually collapses and seals the boring. If it does not, you should fill the boring with a bentonite cement grout.

You can use the cone penetrometer rods to push the piezometer inside an existing cone penetrometer hole. The piezometer does not have the same strength as a cone penetrometer and it will be destroyed if
pushed into medium to hard soils. When pushing the piezometer, you must take piezometer readings to be sure that the pore water pressures created when pushing the cone do not exceed the pressure rating of the piezometer, and you will probably have to push very slowly and stop often to let pressures dissipate before continuing.

The VW piezometer is a sealed unit that is sensitive to any pressure on its diaphragm. It does not distinguish between pressure of the atmosphere and pressure of the water. It responds to both. However, whether this is important or not depends on your application.

Suppose you suspend the piezometer in a standpipe or water well that is open to atmosphere. The piezometer will report the combined pressure of the water and the atmosphere above the water. If your intention is to monitor the level of water in the well, you must correct for variations in atmospheric pressure.

Now suppose you seal the piezometer in a borehole to monitor pore-water pressure. In this case, the pressure acting on the diaphragm is only the water pressure at that depth. Thus you would probably not correct for variations in atmospheric pressure, even if you later found a relation between atmospheric pressure and pore-water pressure.

You can find more about this subject and how to use barometer readings to make corrections in the VW piezometer manual.