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valve mitigates flooding from severe weather events

valve mitigates flooding from severe weather events
Issue Time:2017-09-22

The biggest concern for people outside the affected area following Hurricane Harvey’s assault on the Houston area was the disruption in supply of gasoline and resulting high prices. Approximately one-sixth of total pipeline mileage in the U.S. is in Texas. Many of those pipelines start or end on the Gulf Coast, where about 35 major refineries are located.

At one point, refineries that produce more than 2 million barrels per day of gasoline were taken out of service in the area. While some refineries were up and operating quickly, production was still much lower than normal so there was not enough refined product being created to push product through the system. The same held true for crude oil being pushed through the pipelines to the refineries.

While pumps and valves at the start of a pipeline get crude or refined product moving, momentum or operating pressure is needed to keep it moving through the pipes to the other end where the pumps suck it out. Pipeline operators can reduce pressures to accommodate lower flows, but the types of pumps and valves in the line will determine how low the flow can be before it stops. Some systems can operate at pressures as low as 20%, but that is not the norm.

As valve manufacturers and pipeline operators look to the future as the probability of more catastrophic storms increases, a way forward could be to design process control systems in new or repaired pipelines that can work more reliably in less-than-optimal pressure conditions.

Many people in the paths of Harvey and Irma are experiencing problems from sanitary sewer lines that have backed up and into buildings. They are also dealing with contaminated fresh water sources thanks to flooding of water treatment facilities with not just storm water, but contaminants picked up by the runoff.

“Flooded sewers are stoking fears of cholera, typhoid and other infectious diseases,” reported The New York Times. “Runoff from the city’s sprawling petroleum and chemicals complex contains any number of hazardous compounds. Lead, arsenic and other toxic and carcinogenic elements may be leaching from some two dozen Superfund sites in the Houston area.”

While they may not be able to protect against catastrophic flooding, backflow valves can protect against some incidents. In the case of contamination of the Corpus Christi water system in 2016, faulty or inoperative backflow prevention systems were blamed for the release of indulin and hydrochloric acid into the city’s freshwater system.

There are many designs of backflow valves, ranging from the simple flap or check valves, which allow flow out of the structure but close against reverse flow, to more complex gate valves that produce a stronger seal. Check valves operate automatically while gate valves normally must be operated by hand, at least in residential settings. How effective they are will depend on how much notice the operators have of impending problems.

A device called a backwater valve is available to prevent sewage backups into private homes, but for large commercial properties automated knife gate valves are more common.

In the case of many floods from hurricanes and storm surges, another issue arises—that of freshwater being contaminated by backflow from storm water, irrigation, sanitary discharges and the like. Commercial and industrial buildings as well as municipalities in most states and provinces require backflow prevention systems.

These can be in the form of an air gap, a reduced principle backflow assembly (RPBA), double check valve or a pressure vacuum breaker assembly. Except for the simple air gap, valves play an integral part in backflow prevention systems.

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