Valves play key role in cleaning and maintaining aqueduct pipes

Imagine walking on an inspection tour of a six-foot diameter, dark aqueduct pipe, where the only thing between you and a flood of 160 PSI water is a closed valve. By the way, the nearest exit is a mile away. Reliably holding back that flood of water are 72” Fabri-Valve knife-gate valves from ITT Engineered Valves Group (EGV). That’s the situation at Utah’s Jordan Valley Water Conservancy District (JVWCD), where aqueducts supply raw water from the Uinta Mountain Range to a 180-million-gallon-per-day water treatment plant serving customers and communities throughout a large part of the greater Salt Lake Valley.

Keeping up with demand

The Uinta Mountains are a particularly valuable natural resource, lying to the east of Salt Lake City. The Central Utah Project was constructed to convey water from these mountains to a growing population along the Wasatch front. The aqueduct is a vital component of this project, helping supply high-quality water to more than 950,000 people who live and work in Salt Lake County.

The JVWCD is primarily a wholesaler of water to cities and improvement districts within Salt Lake County. It also has a retail service area in unincorporated areas of the county. Jordan Valley is now the largest municipal water district in Utah, with 90% of its municipal water delivered on a wholesale basis to cities and water districts and 10% on a retail basis to unincorporated areas of Salt Lake County.
As the demand for more water continues to increase in the Salt Lake metropolitan area, keeping the aqueducts clean and capable of delivering maximum flows is a prudent investment - which brings us back to the reason for the inspection tour of the aqueduct.

Cleaning with a "pig"

The inspection tour is precursor to an upcoming cleaning of the entire inside of the 17-mile long aqueduct. As the aqueduct delivers raw water from the mountains, grit, sediment and even moss will coat the inside of the pipe, reducing its flow characteristics.

According to Alan Packard, PE, the Engineering Department manager for the JVWCD, as well as manager of the cleaningproject, the intended capacity of the aqueduct was 270 cubic feet per second (cfs). The deposits on the pipe, however, have reduced that flow to 240 cfs. While that may not sound like much, it actually amounts to a loss of almost 20 million gallons per day in flow capacity.

During the first weeks of December, the JVWCD will initiate a cleaning process called "pigging" to scour the interior of the pipe and remove the layer of sediment. This will be accomplished by running a cylindrical foam device covered with bristle-imbedded urethane through the pipe. The device is called a "pig." The pressure of the water flow behind the pig forces it through the aqueduct.

How the "pig" got its name isn’t exactly clear. A spokesperson at the Pigging Products & Services Association (PPSA) noted that when these devices were first used in Texas around 1870, they were made of bundles of leather. When they came out of the ends of the pipes they were cleaning, they squealed, just like the real thing - and an industry was born. Originally developed to remove deposits that could obstruct or retard flow through a pipeline, pigs are now used for many different reasons, and in all phases of the life of a pipeline.

The JVWCD recently used the pigging process to clean a 12-mile section of another 78”-diameter aqueduct with great success. Test results after the operation showed that the aqueduct flow capacity increased 22.5 percent from 129 million gallons per day to 158 - an increase of 29 million gallons per day (exceeding the estimated 20 million gallons per day expected). Similar results are expected after the December cleaning of the 17-mile section of aqueduct.

Easing Minds

When the aqueduct was originally constructed, 72” butterfly valves were installed throughout its length. Because the pigging device takes up the entire area of the pipe, the pig would not be able to pass by the butterfly valves. In the summer of 2003, all three butterfly valves were replaced by Fabri-Valve bonneted knife-gate valves from ITT EVG. The gate of the valves fully retracts and provides an unrestricted full flow port, which allows the pig to pass through. But, what’s good for the pig also seems to be pretty good for the people who work with the Jordan Valley Water Conservancy District - especially those who take part in those inspection tours inside the pipe.

As Alan Packard points out, "We expect that after the pigging operation is complete, we will walk and inspect it to see how well the cleaning has been done. If needed, we can do an additional pass." While the knife-gate valves are seldom operated - being held mostly in the "open" position - they’re still on constant duty. They need to work perfectly. ITT offers bonneted Fabri-Valve knife-gate valves for difficult applications, including buried service requiring gate protection, and high-cycle stem sealing. The cylindrical packing around the stem provides a tight, easy-to-maintain seal.

The 72" valves used in Jordan Valley Water Conservancy District aqueduct project incorporate the following features:

• 304 stainless steel wetted components and carbon steel exteriors
• bonnets to protect the gate and a dirt shields to protect the actuation;
• dual, replaceable neoprene seats;
• special seat protectors to shield the soft neoprene seats from the abrasive bristles of the pig;
• electric actuators.

In addition to this type of raw water service, these knifegate valves can be used for handling process fluids in pulp & paper, chemical, petroleum, refining, mining, wastewater, power and marine applications.

The Engineered Valves Group is unit of ITT Engineered Process Solutions Group (EPSG). EPSG is a leader in valve technology, innovation and design, meeting the critical needs of its customers on a worldwide basis. EPSG delivers valve solutions for a full range of industrial flow control needs including chemical processing, power generation, pulp and paper, water treatment, pollution control and pharmaceutical and bioprocessing