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Drawdown Gauge By Ametek A566. PG-45-WL

Drawdown Gauge By Ametek A566. PG-45-WL
Code: A566
Price: $32.00
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This is a Gauge used for measuring  water levels in a well up to 390' deep. The gauge is 4.5" across and has a 1/4" N.P.T. external thread. It comes with directions in the box. Find below a great article on how this gem works.


Reference: Ground Water and Wells

Published by Johnson Division, Universal Oil Products Company St. Paul, Minnesota 55165 (Pages 90 and 91)

Figure 1 shows the installation of an air line in a well for the purpose of determining the depth to water. The air line consists of a small diameter pipe or tube of a length sufficient to extend from the top of the well to a point several feet below the lowest anticipated water level to be reached during the life of the well. The exact length of the air line must be measured as it is placed in the well. If flexible tubing is used, steps must be taken to be sure that the tubing hangs vertically in the well and does not spiral inside the well casing. The air line must be completely air tight throughout its entire length and connections to it at the ground surface must be air tight.

Quarter-inch copper or brass tubing is commonly used for the air line. The upper end of the air line is fitted with suitable connections and valve so that an ordinary tire pump can be used to pump air into the tube. A tee is provided in the line to which a pressure gauge may be connected to measure the air pressure in the tube. A gauge calibrated to indicate pressure in feet of water serves better than one with a scale reading in pounds per square inch (psi).

The device works on the principle that the air pressure required to push all of the water out of the submerged portion of the tube equals the water pressure of a column of water of that height. If this pressure is expressed in feetof water, the depth to water can be calculated.

A necessary first step is to determine accurately the depth from the top of the well casing or from some other reference point to the lower end of the air line. Once installed with the pressure gauge connected, air is then pumped into the line. The pressure shown by the gauge increases until it reaches a maximum value, which means that all the water has been forced out of the air line. At this point the air pressure in the tube just balances the water pressure and the gauge reading shows the pressure necessary to support a column of water of a height equal to the distance from the water level in the well to the bottom of the tube. If the gauge indicates feet of water head, then it shows directly the submerged length of the air line in feet. Subtracting the submerged length from the total length of the air line gives the depth to water below the measuring point chosen.

A measurement made before starting to pump the well indicates the static water level. Any change in water level is represented directly by a difference in pressure shown by the gauge in subsequent measurements. Drawdown during pumping and during recovery after pumping is stopped, can be readily recorded from the pressure readings.

Referring to Figure 1, the depth to water is always calculated from the following formula:

d = L- l

where d = depth to water in feet.

L = depth to bottom of air line in feet.

l = pressure head in feet represented by a column of water of height equal to the submerged length of the air line.

Suppose we have an installation where the distance from the top of the well casing to the lower end of the air line is 95 feet. As the air is pumped slowly into the line assume that a maximum reading of 46 feet on the pressure gauge is reached. The depth to water is then the difference between 95 feet and 46 feet or 49 feet. Let’s say that this is the static water level.

Assume now that the pump is started. As the water level in the well drops, the submerged length of air line decreases and the pressure indication on the gauge drops accordingly. A gauge reading of 34 feet, for example would mean that the submerged length of the air line has decreased by 12 feet and the depth to water has changed to 95 - 34, or 61 feet. This indicates a drawdown in the well of 12 feet below the static water level, Each reading must be multiplied by 2.31, if the gauge reads in psi, to convert it to feet of water. A reading of 15 psi for example corresponds to a pressure head of 15 .X 2.31, or 34.6 feet of water.

The dependability of the measurements made by the air line device varies with the accuracy of the pressure gauge and the care used each time in operating the tire pump to get the pressure reading. Depth to water can be determined usually within 0.2 feet of the exact value. The air line is not accurate enough for use in observation wells during an aquifer test, but it is the most practical means for measuring water levels in a pumped well. To avoid disturbances from turbulence near the intake of the pump, the lower end of the air line should be at least five feet above or below the point where water enters the pump.


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Installation of an Air Line
Figure 1