One place where valves are used that touches every one of us every day of our lives is the clean water industry. When we turn on the tap for a drink or open the hydrant to water our roses, we are interacting with the last valve in the clean water pipeline. The valves used in this piping-intensive, complicated industry perform yeoman’s duty behind the scenes and often behind security fences—24 hours a day.
AT THE BEGINNING
But where does the pipeline start? Where does the drinking water, also called potable water, come from?
Drinking water comes from two primary sources—surface water (rivers, lakes and ponds) and sub-surface water (wells). In most cases, the easiest water to prepare for human consumption is well water. This is because water from deep-shaft wells is obtained from aquifers that run through acres and acres of subterranean sand and rock. This porous material provides an excellent method of filtering the water to nearly ready-to-drink conditions. All that is needed is a method of pumping the water to the surface. What’s more, the free-flowing artesian wells don’t even need a pump. Because of retained pressure in the aquifer, this drinking water freely flows to the surface.
Although well water is sometimes consumed as it comes from the ground, when it’s used in municipal water systems, the water is usually disinfected with chlorine before traveling down the pipeline.
With surface water, which requires the most effort to get ready for consumption, water purification plants need to treat the water, so the systems are much larger and more complex than those that only treat deep well water.
GETTING TO PURE
The first step in surface water purification is getting the water to the treatment plant or the water works, as some call it. It is always cheaper if the facility is close to the water source and at a lower elevation so that expensive pumping systems don’t have to transport the raw water to the treatment plant. The water that is transported to the treatment facility goes through either open canals or closed piping systems. Untreated water is usually not corrosive, so the choice of pipe materials is broad: concrete, iron, polyvinyl chloride (PVC), reinforced concrete pipe (RCP), high-density polyethylene (HDPE) or fiberglass.
Historically, the materials of choice were concrete pipe and iron gate valves. Today, thermoplastics and resin piping materials are most often specified for large outside diameter (OD), low-pressure lines. The on/off valve of choice is the ductile iron, resilient-seated butterfly valve, because it takes up little space, and the iron is slow to rust. However, some systems still are built with large OD ductile iron gate valves for on/off applications. All the valves in this part of the system, as well as most valves in the entire purification plant, are built in accordance with American Water Works Association (AWWA) standards.
Surface water can arrive at the treatment facility containing a large variety of contaminants that must be removed—the term applied to describe these suspended particles is turbidity. The large particles of suspended matter in raw water are removed by allowing them to settle in large, very-low-flow sedimentation basins. However, the smaller ones, which are called nonsettleable solids, require some form of artificial coagulation. These smaller solids must be removed because they consist of bacteria, viruses, protozoans, organic matter and inorganic solids.
The process of coagulation assistance, which is called flocculation, requires injection of special chemicals into the water to help these miniscule contaminants settle out. A typical flocculation chemical formulation is aluminum sulfate with a 2% copper sulfate blend. In smaller to mid-size systems, these chemicals are added to the water by peristaltic pumping systems. These low-pressure systems often use PVC, HDPE or RCP plastic pipe and valves.
The large settling tanks themselves are fed from large OD piping systems. Plastic or fiberglass pipe can be used, but steel, cast iron and even stainless steel is also specified. The valve of choice in these lines is water purification’s most valuable player: the resilient-seated butterfly valve.
The piping to and from these tank systems is redundant to allow for periodic shut-down and cleaning of individual tanks to remove the “floc” from the bottom of the system. This floc is a sludge-like material that must be removed and disposed.
After sedimentation, the “cleaner” water is pumped through a large filtration system to remove additional suspended material. Like the sedimentation tanks, the filtration tanks are individually piped to allow frequent cleaning, and there is substantial piping connecting to and bypassing each individual filter tank assembly. The resilient-seated butterfly valve is found here as well.
Following the filtration process, a disinfectant is added to the water. In the United States, the most common disinfectant used is chlorine, and the process is called chlorination. Chlorine is a highly volatile, hazardous fluid that must be handled carefully. The complexity of the chlorine piping depends on the volume of the system. Very large municipalities will have chlorine delivered by railcar, whereas smaller facilities will use pressurized containers delivered by truck.
Chlorine piping systems are designed in accordance with specifications published by The Chlorine Institute. Because of the high volatility, all chlorine valves should be constructed of materials that will resist corrosion by the specific chlorine product used.
Once water passes through the disinfectant stage, it is ready for distribution. Unless the facility is high above the point of use, the purified water needs to be pressurized for delivery. This is accomplished by pumping systems that will either pump water into a water tower to create “head pressure,” (usually about 40 psi) or pumped to pressurize the water mains. Main pressures charged through a pumping system usually range from 50-80 psi. The discharge piping from the treatment plant is often a large OD system, from 36-60 inches (and larger for major municipalities).
Most cities will also incorporate large storage tanks to keep an ample supply of clean water on hand. The piping systems for distribution are also designed and built of materials in accordance with AWWA standards.
Although a water purification system could be operated manually, it is much more practical to automate the plant with a Supervisory Control & Data Acquisition (SCADA) system. Using a SCADA system helps the utility keep track of data and eliminates requiring operators to manually read and record information.
The basic processes in a water purification plant are straightforward and can be broken down into a number of separate control loops. As in most control loops, there is a final control element. In this case the final control elements are primarily actuated butterfly valves. Since there are mostly gross flow rates to stop and start, the fine tuning of precise control valves is generally not needed, except perhaps in the case of chemical injection.
Seawater and brackish-water desalination is an underused source of clean water today, although large-scale operations have been in existence for over 50 years. The facilities for desalination are much more complex, and the piping systems more robust than standard water purification plants.
Congress passed the Saline Water Act in 1952, which provided support for desalination projects. The first large-scale desalination plant was installed in Freeport, TX in 1961 by the Dow Chemical Company. This facility provided over a million gallons of clean water per day for the plant as well as the city of Freeport for many years. Several additional desalination plants are now in the design stage for installations on the east and west coasts as well as the gulf coastline.
Desalination occurs through two major methods: the membrane method and the thermal method. Here in the U.S., the membrane method, which is primarily reverse-osmosis, is the most popular. In other parts of the world, the thermal method, which is heat-based, is more widely used. Both desalination processes require much more energy than conventional water treatment processes. For example, the thermal method, which relies primarily on distillation technology and requires heat generation and heat-transfer equipment, results in facilities that look more like small refineries than water treatment facilities. The reverse osmosis process, on the other hand, requires high-pressure piping systems in the 400-500 psi pressure range, which means piping specifications that are closer to refinery or chemical plant requirements.
Regardless of type, desalination plants offer valve manufacturers and suppliers a good opportunity for diversifying valve sales.
THE STATE OF AFFAIRS
While every municipality in the United States has water systems, some are in better mechanical and financial shape than others. It is generally accepted that updating our nation’s water purification systems is part of the huge overall infrastructure improvement that is becoming critical in this country. The American Society of Civil Engineers has looked closely at this aging infrastructure and given drinking water facilities in the U.S. an overall grade of D-. The giant mammal in the room that can’t be ignored, however, is the cost for the critically needed work during a time when budgets are already tight.
One of Texas’ medium-sized municipalities that serves as a good example for trying to stay ahead of the problem is Beaumont, a petrochemical and refining hub on the Texas Gulf Coast. According to Dr. Hani J. Tohme, that city’s water utilities director, the utility infrastructure problem is magnified by a lack of visibility.
“The (water) infrastructure has been neglected in our country [because] you can’t see it [the water system]—it is underground—but you can see a pothole,” he said. This explains why in some cities asphalt trucks cruising around making repairs to streets are a frequent site, while water main problems go untouched.
Dr. Tohme adds that the solution to the water utility infrastructure problem is easy to fix: “You have to have rate increases.” Beaumont has not been afraid to do that and has also not been afraid to spend: The city spent $11 million on water system upgrades since 2002, which easily accommodates Beaumont’s water needs through the next decade. He also says that purchasing quality equipment is important for good stewardship of public funds and to that end, a strong “made in USA only” valve and piping policy is a necessity. ”As a municipality there should be support of domestic-made products,” he says.
FOR THE REST OF US
Staying ahead of costs will be virtually impossible across the country unless more revenue is generated. According to the Environmental Protection Agency, estimates of capital needs for drinking water improvements over the next 20 years are $334 billion, which does not include the costs associated with meeting the Clean Water Act requirements that affect clean water costs.
The positive side to the huge infrastructure needs is that those needs equate to large orders for equipment manufacturers, including those in the valve industry. As long as ample money flows into the fiscal municipal pipeline, much-needed clean water should continue to flow through the valve-laden water pipelines as well.
Special thanks to Dr. Hani J. Tohme, P.E., water utilities director and Barry W. Miller, superintendent, Water Treatment Plant for the City of Beaumont, for their cooperation in preparation of this article.