Did you ever wish you could stick your head in a pipe and inspect it visually? You can do just that with a tiny closed-circuit television (CCTV) camera mounted on wheels or tracks. You can introduce this device into a pipe through any inspection point. Using CCTV to inspect pipes means you can track down root incursions, crushed pipe and other issues and see exactly what – and how extensive – the damage underground is. (It's important to understand all the factors involved in a project. For more, see The Geotechnical Investigation: Which Method Should We Use?)
What Is CCTV?
Closed circuit television is not a new technology; it dates back to the 1950s. In CCTV, the television camera is hardwired to a receiver. One of the first applications of CCTV was in security, where cameras spread across a large area or throughout several rooms were routed to a single television receiver for a bank of television receivers. This enabled one person to monitor many areas at a time.
What Makes up a CCTV Crawler?
A CCTV crawler consists of a camera, a control/video cable, a video receiver, a mobility system of tracks or wheels and a control system to move the crawler backward, forward or around corners.
The camera can be as small as a hearing aid battery and transmits in color for maximum inspection value. The color camera used in sewer crawlers is known as a charge-coupled device, or CCD. It’s the same type of transistor (yes, it is a transistor) used in digital cameras and cell phones. It can record motion or take still shots without a grainy appearance that might cause you to miss details.
The “closed circuit” nature of the system is based on the cable that runs from the CCD to the video receiver outside of the pipe. This coaxial cable consists not only of the CCTV signal, but also includes a separate wire that carries the signal from the operator’s control station (outside of the pipe) to the crawler that allows the operator to move the crawler forward or backward within the pipe, or to change direction to inspect laterals.
The mobility system consists of a frame to hold the camera and tracks or wheels, depending on the crawler design chosen. It may or may not be equipped with an LED lighting system since some CCDs can operate in an extremely low-light environment. The mobility system also includes the electric motor(s) that drive the tractor wheels. Crawlers that can change direction laterally may have two motors which operate independently and allow one track (or the wheels on one side) of the crawler to move in one direction while the track (or wheels) on the other side of the crawler move in the opposite direction, allowing the crawler to turn either left or right.
The video receiver is a small computerized unit that interprets the image sent from the CCD and displays it on a screen.
The operator control station may be as complex as the latest Xbox, complete with the joystick control, or it may be as simple as two three-position switches – one for the track or wheels on the left side of the crawler, the other for the track or wheels on the right side of the crawler. With the joystick control, the operator merely moves the joystick in the direction he wants the crawler to move. With the three-position switch control, if both switches are moved to the forward position, the crawler will move forward; if both are moved to the reverse position, the crawler will move backward. If the left switch is moved to the forward position and the right switch is moved to the backward position, the crawler will turn to the right, and to turn the crawler to the left, the right switch is moved to the forward position and the left switch rearward. (For another method of pipe inspection, check out A Look at Pipe Penetrating Radar.)
Sounds Good, but Is Pipe Inspection by CCTV Ever Not a Good Idea?
The smallest crawlers can fit into a pipe with an interior diameter of only 1½ inches. Because the crawler offers you the advantage of being able to define both the nature and the extent of damage to the pipe, you can avoid making repairs that are “too extensive” and too costly. You can also avoid making repairs that are inappropriate, for example, installing a pipeline when pipe bursting at a new section of pipe is called for. The only time a pipe inspection by CCTV is not recommended is when the homeowner or business doesn’t want it or can’t afford to pay for it. In either of these cases, the money the property owner saves by not doing too much or too little more than makes up for any added costs resulting from the CCTV inspection. This means that any way you look at it, using CCTV to inspect pipe is a good deal.