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Human Factors Can Cause a Disaster—or Prevent One

Human Factors Can Cause a Disaster—or Prevent One

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Improving Valve Sealing Performance and Reliability

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A Primer on Fugitive Emissions

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Industry Headlines

Industry Headlines

Emerson Expanding Mississippi Facility

3 DAYS AGO

Emerson plans on delivering $500,000 in new equipment to its facility in Sherman, MS. Because of this investment , and its promise of new jobs for the region, the Sherman Economic Development Corp. has approved $150,000 in grants for Emerson.

"We have a relatively new Fisher product that will be reloca...

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REXA and CCC Form Joint Initiative

3 DAYS AGO

REXA and Compressor Controls Corporation (CCC) have formed a joint initiative to modernize steam turbine controls for enhanced performance based upon each company’s core competency.

There are more than 10,000 turbomachinery trains worldwide powered by CCC. By upgrading mechanical and hydraulic go...

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Energy Transfer Partners Building New NGL Fractionation Facility

-1 DAYS AGO

Energy Transfer Partners’ subsidiary, Lone Star NGL LLC, will construct a fifth natural gas liquids (NGL) fractionation facility at Mont Belvieu, TX. The construction of Fractionator V is a result of the tremendous production growth in the Delaware and Permian Basins.

Fractionator V, including NG...

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Chevron and Pembina Sign Deal to Build Pipelines, Other Facilities

3 DAYS AGO

Calgary-based Pembina Pipeline Corp. has signed a 20-year deal with Chevron to build natural gas pipelines and processing facilities for a potential production operation in northwest Edmonton, Alberta. The infrastructure developed over the term of this agreement has the potential to represent a multi-...

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Kansas City Fed Survey Shows Regional Manufacturing Jump

-1 DAYS AGO

According to Chad Wilkerson, vice president and economist at the Kansas City Fed, the district’s February Manufacturing Survey revealed that manufacturing activity expanded further with continued strong expectations . The Federal Reserve Bank of Kansas City serves the tenth Federal Reserve Distr...

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U.S. Private Sector Growth Slows from January’s 14-Month Peak

3 DAYS AGO

At 54.3 in February, the seasonally adjusted Markit Flash U.S. Composite PMI Output Index dropped from 55.8 in January but remained above the 50.0 no-change value for the twelfth consecutive month. The latest reading signaled that private sector output growth moderated from the 14-month high recorded ...

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Water Hammer—Check It Out

Have you ever been in an area of the plant that had just shut down a pump, only to hear an explosive sound a few seconds later? The noise you heard was the pump check valve, accompanied by the water hammer, or reverse flow, that slammed it shut.

Multiple pump systems often use a check valve located between the pump and the discharge header. The purpose of this valve is to prevent backflow from the header to the pump when it is not running. Without the check valve the pump could actually spin backwards.

Depending on the system pressure, these valves can close with such force that they damage the check valve, the pump, and over time even the pump base. Most check valves require reverse flow to close the valve and once this flow momentum has started, it does not stop as quickly as the check valve closes. The result is water hammer, a very destructive force. According to Webster's: Water hammer: a concussion, or sound of concussion, of moving water against the sides of a containing pipe or vessel.

We have seen many plants overcome these laws of physics with the use of an "auto check," also known as a "butterfly check." This concept utilizes a pneumatic-operated butterfly valve, and relatively simple control logic in order to close the valve automatically, prior to shutting down the pump. This action avoids reverse flow, so that the back flow and water hammer never have the chance to develop.

The valves for these applications are typically high-performance butterfly valves with a pneumatic actuator. Accessories include a limit switch and four-way pilot solenoid with two adjustable speed controls. The speed controls restrict the airflow out of the cylinder in both directions, thus regulating the opening and closing speed of the valve.

Control logic for the auto check is simple. When the pump is not pumping, the butterfly valve is closed. When the motor start command is received, either locally or from the PLC, the pump motor is energized. Pressure builds up on the pump side of the auto check valve. A differential pressure switch senses pressure differential between the newly started pump and the header past the auto check. At some predetermined point-such as 1 psi, .5 psi. or .25 psi-the delta p switch makes contact on pressure increase. The switch is sealed in by a relay and energizes the solenoid valve, which opens the butterfly valve smoothly, aided in part by the speed control valves. When the butterfly valve is totally open, a limit switch is tripped and sends a valve-open status to the PLC.

When the motor stop command is received, the pilot solenoid is de-energized and the valve closes at a controlled rate, again aided by the speed controls. When the valve is completely closed the limit switch is tripped, which in turn shuts off the pump motor. This action eliminates water hammer by preventing any back flow from occurring.

BRUCE FENWICK is in technical sales for McJunkin Corporation, Harvey IL. Reach him via 708.225.3120 or at This email address is being protected from spambots. You need JavaScript enabled to view it..

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