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Last updateFri, 21 Jul 2017 2pm

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Monitoring Valve Health via the Internet

Monitoring Valve Health via the Internet

Most valve end users are already using s...

Valves in Oxygen Service

Valves in Oxygen Service

In his presentation at VMA’s 2017 ...

Thermal Spray Coating

Thermal Spray Coating

Q: What are the pros and cons of us...

Ball Valve Repair 101

Ball Valve Repair 101

From time to time, we are re-posting wel...

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Industry Headlines

LyondellBasell to Build the World's Largest PO/TBA Plant

Friday, 21 July 2017  |  Chris Guy

LyondellBasell has made the final investment decision to build the world's largest propylene oxide (PO) and tertiary butyl alcohol (TBA) plant in the ...

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How to Choose the Best Rapid Prototyping Method

How to Choose the Best Rapid Prototyping Method

Tuesday, 18 July 2017  |  Kate Kunkel

As new products are designed, including valve bodies and the parts that comprise the finished valve, prototypes must be created. How that is achieved ...

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Industry Headlines

Badger Alloys Joins VMA as Associate Member

5 DAYS AGO

This week the Valve Manufacturers Association (VMA) welcomes Badger Alloys as an official associate supplier member. This is VMA’s fourth new member in 2017.

Located in the heart of Milwaukee and founded in 1966, Badger Alloys offers single source capabilities for custom castings. The company pou...

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Thermodyn Joins VMA as Associate Member

5 DAYS AGO

This week the Valve Manufacturers Association (VMA) welcomes Thermodyn Corporation as an official associate supplier member. This is VMA's third new member in 2017.

In 1979, Thermodyn began business with the dual purpose of selling A.W. Chesterton products and manufacturing high-temperature elastomers ...

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LyondellBasell to Build the World's Largest PO/TBA Plant

2 DAYS AGO

LyondellBasell has made the final investment decision to build the world's largest propylene oxide (PO) and tertiary butyl alcohol (TBA) plant in the Houston area. The project is estimated to cost approximately $2.4 billion, representing the single-largest capital investment in the company's history...

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EPA Selects Projects for Water Infrastructure Loans

3 DAYS AGO

The EPA is inviting 12 projects in nine states to apply for Water Infrastructure Finance and Innovation Act (WIFIA) loans. These potential applicants were selected from a group of projects that represent large and small communities from across the U.S. that submitted letters of interest to EPA in Ap...

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Leading Economic Indicators Increased in June

2 DAYS AGO

The Conference Board Leading Economic Index (LEI) for the U.S. increased 0.6% in June to 127.8 (2010 = 100), following a 0.2% increase in May, and a 0.2% increase in April.

“The U.S. LEI rose sharply in June, pointing to continued growth in the U.S. economy and perhaps even a moderate improvement...

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U.S. Jobless Claims Fall to Near Five-Month Low

3 DAYS AGO

In the week ending July 15, the advance figure for seasonally adjusted initial claims was 233,000, a decrease of 15,000 from the previous week's revised level. The previous week's level was revised up by 1,000 from 247,000 to 248,000. The 4-week moving average was 243,750, a decrease of 2,250 from t...

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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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