Robotic underwater viewing systems provide a cost-effective method for assessing the condition of water storage tanks without taking them out of service.
Water tank inspection can be a costly process, often requiring tanks to be drained and taken out of service. Finished water is wasted and service to customers can be disrupted.
Aquabotix Technology Corp. has developed an alternative in a robotic inspection system that can be sterilized, inserted into the tank and driven around using computerized controls. It’s the same basic concept as in video pipe inspection cameras, except that this system operates in three dimensions instead of on a linear course. One version of the device includes rotating brushes that can actually scrub deposits off the tank walls.
Durval Tavares, company president, worked 20 years on underwater technology with the Naval Undersea Warfare Center in Newport, R.I. After a career change to the financial sector, he returned to his roots in the water business, aiming to develop products that would make a difference in people’s lives. That includes making work life easier for people who inspect potable water tanks.
“Being able to see the condition of those tanks helps water authorities extend tank life and provide higher-quality water service to consumers,” Tavares said. He talked about the Aquabotix technology in an interview with Water System Operator.
WSO: Without this technology, how are water tanks inspected?
Tavares: One way is to empty the tank and have people enter through a hatch and check it out. The problem is you have to shut off the water supply from that tank while you do the inspection. You also waste a lot of water by dumping it so you can do the inspection.
Another way is to put a diver into the tank. That can be a costly and complicated process because you’re putting a human being inside the fresh water supply. The person doing the inspection and the equipment have to be bathed in a disinfectant solution. You’re also putting the diver at risk because inside these tanks it’s easy to lose track of where you are. It looks the same everywhere you go.
WSO: What are the specific advantages of your approach to inspections?
Tavares: Our vehicles record exactly what the inside of the tank looks like so that the water authority can make decisions on good information. There are no lubricants and no other pollutants on the vehicle. It’s made of metal and ABS plastic. We recommend that the vehicle be doused in a chlorine solution before placing it in the tank so they don’t risk contaminating the water.
WSO: Please describe how these vehicles work.
Tavares: We make two vehicles for water tank inspections – an entry-level HydroView Inspector and a higher-end HydroView Professional. Both can go down to 250 feet. They come with two cameras, one in front and the other mounted on top of the vehicle. That second camera can be aimed in any direction. You can swim the vehicle along the inside of a tank, and as you do that you can have the top-mounted camera facing at 90 degrees to the travel direction, so you can record the condition of the wall as you travel around. Both models record high-definition digital video and high-definition still images on an internal memory. After the inspection you can go back, review the recording and select the pictures to include in a report. The vehicles have depth sensors, temperature sensors and heading sensors that tell you the direction of travel, as with a compass. They come with an internal LED light, and 800 lumens of external LED lighting can be added.
WSO: What is the method of propulsion and steering?
Tavares: The Inspector model has three high-precision Swiss-made motors. A rear propeller lets you control the pitch of the vehicle, and two front propellers let you control forward/backward motion and turning. The Professional model has eight motors. Three are dedicated to hovering and one controls lateral movement. For the remaining four motors, you have all four control forward/backward movement, or have two for forward and back and put brushes on the other two. Then if you see a buildup on the tank wall, you can have the brushes scrape it off so you can inspect and see what is underneath. The motors spin at up to 3,000 rpm. One rotates clockwise and the other counterclockwise. If they both turned in the same direction, the vehicle would walk the wall and you would lose control.
WSO: What is the power source for the vehicles?
Tavares: They are powered by built-in lithium-ion batteries that are fully sealed. Battery life is two to three hours, which is plenty of time to complete a tank inspection.
WSO: How does the inspection operator control the vehicle?
Tavares: They need to be tethered because Wi-Fi and radio signals will not travel through water. The vehicles can pull a cable length up to 500 feet. The cable can extend from the ground to the top of the tank and into the tank. A person standing on the ground can control the vehicle. The operator can use a PC and a game-console-type control box with joysticks, or control the vehicle with an iPad. In that case, they can actually turn the vehicle left and right, up and down, by turning the iPad.
WSO: What has been the market’s reaction to this technology?
Tavares: There has been a lot of interest. We’ve delivered several to water authorities, and we’ve had contractors who do water tank inspections purchase them. Tank inspection companies find that they can provide a better service to customers because they can do the job quicker and with less impact on the customer’s operations.
WSO: Does it take a large water utility to justify the purchase of a vehicle?
Tavares: No. A tank inspection typically costs $1,500 and up. If you inspect 10 tanks, you have essentially paid for a HydroView Professional right there.
WSO: What other applications does this technology have?
Tavares: It can be used to inspect water intakes for water treatment plants and the water intakes and outlets for power plant cooling systems. Otherwise it can be used for anything from marine craft inspection, to search and recovery efforts, to inspecting tanks in aquaculture.