Pipehorn Valve Box Finder Model 400
An attachment for locating valve boxes or manhole covers
Use with your Model 100 or Model 500 Receivers
Locating a Cover
Once the Valve Box Finder (VBF) has been attached, and the line under the cover has been located, switch off the main transmitter. Turn on the VBF and adjust the receiver's sensitivity to get a shrill (high pitched) sound.
Holding the receiver vertically and close to the ground, scan the area and listen for the tone to go deep or beeping. This indicates the presence of a metal object. To pinpoint the center of the object, adjust the sensitivity to get a sharp null at the center (as shown below). To determine the size and shape of the object, adjust the sensitivity so that you can trace the edge of the cover (as shown below).
Pinpoint The Center
Tracing the Edge
The Valve Box Finder is an inexpensive attachment that fits on your Model 100 or Model 500 Receiver. Simply attach this unit as shown below and locate large metallic objects such as manhole covers and valve boxes that have been paved or backfilled over.
The advantages of using this attachment vs. a standard metal detector, is that it will not pick up the smaller items such as coins and nails. Instead it is looking for large disturbances in the earth's magnetic field.
No separate transmitter is needed to use this item. Once attached, it and your receiver are a self contained locator. For maximum depth and range, rotate the tube and increase the receiver sensitivity to achieve the sharpest null possible.