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Last updateFri, 26 May 2017 2pm

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The Future of Coal: Efficiency Over Politics?

The Future of Coal: Efficiency Over Politics?

Many changes in the power industry have ...

Valve World Americas Event Set for June 20-21

Valve World Americas Event Set for June 20-21

End users, distributors, EPC/AEC personn...

Water Hammer

Water Hammer

Water hammer is a shock wave transmitted...

Turning the Tables on Valve Corrosion

Turning the Tables on Valve Corrosion

Multiple valve manufacturers and users w...

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Industry Headlines

Emerson Acquires MYNAH Technologies

2 DAYS AGO

Emerson has completed the purchase of MYNAH Technologies, a long-time Emerson alliance partner. The addition of MYNAH will help support Emerson Automation Solutions and its Operational Certainty program. Terms of  the acquisition were not disclosed.

MYNAH software is currently in use at more than ...

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Roger Fix Named Chairman of Flowserve

3 DAYS AGO

In its most recent annual meeting, Flowserve announced that Bill Rusnack and Lynn Elsenhans have retired as members of the board of directors. Flowserve also announced that board member Roger Fix has been elected to replace Rusnack as chairman.

"Bill and Lynn provided years of distinguished service to ...

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Oil-Fired Plants Provide Small Amount of U.S. Electric Capacity, Generation

1 DAY AGO

According to the U.S. Energy Information Administration , roughly 70% of petroleum-fired electric generating capacity that still exists today was constructed prior to 1980. Utility-scale generators that reported petroleum as their primary fuel comprised only 3% of total electric generating capacity at...

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ExxonMobil, SABIC Agree on Proposed Petrochemical Project

3 DAYS AGO

Affiliates of Exxon Mobil and SABIC (Saudi Basic Industries Corporation) signed an agreement to conduct a detailed study of the proposed Gulf Coast Growth Ventures project in Texas and begin planning for front-end engineering and design work. The agreement was signed during the Saudi-US CEO Forum in R...

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Kansas City Fed Manufacturing Survey Shows Expansion in May

10 HOURS AGO

Tenth District manufacturing activity continued to expand at a moderate pace in May, and expectations for future activity increased strongly. Price indexes were mixed, but recorded little change overall. The month-over-month composite index was 8 in May, up from 7 in April but down from 20 in March.

Ac...

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Business Borrowing for Capital Investment Up 8% in April

1 DAY AGO

The Equipment Leasing and Finance Association’s (ELFA) Monthly Leasing and Finance Index, which reports economic activity from 25 companies representing a cross section of the $1 trillion equipment finance sector, showed their overall new business volume for April was $7.9 billion, up 8% year-ov...

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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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