10212017Sat
Last updateThu, 19 Oct 2017 5pm

i

Market Outlook 2018: A Sunnier Mood with a Few Caveats

Market Outlook 2018: A Sunnier Mood with a Few Caveats

The atmosphere at VMA’s 2018 Marke...

Is it Time to Toss Those Commissions?

Is it Time to Toss Those Commissions?

It’s tough to pinpoint exactly wha...

Cybersecurity for Process Control

Cybersecurity for Process Control

Security for any process plant has alway...

Young Valve Professionals: Megan Johnston

Young Valve Professionals: Megan Johnston

In 2014, VMA's leadership created the Val...

Subscribe SUM17

FREE SUBSCRIPTION*

• Print magazine
Digital magazine
• VALVE eNews
Read the latest issue

*to qualified valve professionals in the U.S./Canada

The Weekly Report

New Products

  • ja-news-2
  • ja-news-3

Industry Headlines

Crude Oil, Petroleum Product Exports Reach Record Levels

Thursday, 19 October 2017  |  Chris Guy

According to the U.S. Energy Information Administration ( EIA ), crude oil exports in the first half of 2017 increased by more than 300,000 barrels per ...

Readmore

Loading...
Advertisement
i

Industry Headlines

Emerson Agrees to Acquire Paradigm

2 DAYS AGO

Emerson has agreed to acquire Paradigm for a purchase price of $510 million, reflecting a multiple of 13 times expected 2017 EBITDA. Paradigm will be joined with Emerson’s existing Roxar automation software. The acquisition is expected to close within the next 60 days, subject to various regulat...

Readmore

ValvTechnologies Receives ISO 15848 Certification

3 DAYS AGO

ValvTechnologies’ EcoPack technology has received ISO 15848-1:2015 certification from Odin Heavy Industries. To earn ISO 15848 certification, ValvTechnologies underwent a stringent evaluation process that included a series of 17 helium leak tests and eight thermal cycles on a fully assembled v...

Readmore

Crude Oil, Petroleum Product Exports Reach Record Levels

1 DAY AGO

According to the U.S. Energy Information Administration ( EIA ), crude oil exports in the first half of 2017 increased by more than 300,000 barrels per day (b/d) from the first half of 2016, reaching a record high of 0.9 million b/d. Petroleum product exports also grew over the same period with propan...

Readmore

Energy Intensity in U.S. Manufacturing Decreased

1 DAY AGO

Energy intensity in manufacturing in the U.S. decreased from 2010 to 2014. U.S. manufacturing overall fuel intensity decreased by 4.4% from 3.016 thousand British thermal units (Btu) per dollar of output in 2010 to 2.882 thousand Btu in 2014. According to the Manufacturing Energy Consumption Survey (M...

Readmore

Fed Reports Economy Growth in September, Early October

1 DAY AGO

Reports from all 12 Federal Reserve Districts indicated that economic activity increased in September through early October, with the pace of growth split between modest and moderate. The Richmond, Atlanta, and Dallas Districts reported major disruptions from Hurricanes Harvey and Irma in some areas a...

Readmore

Industrial Production Up 0.3% in September

2 DAYS AGO

Industrial production rose 0.3% in September. The rates of change for July and August were notably revised; the current estimate for July, a decrease of 0.1%, was 0.5% lower than previously reported, while the estimate for August, a decrease of 0.7%, was 0.2% higher than before. Manufacturing output...

Readmore

Those Dam Valves and the Great Job They Do

vmsum12_dam_1A settling pool helps to dissipate the energy from the submerged output of turbine discharge lines.As the nation increasingly seeks sources for renewable energy, dams and the thousands of valves they contain will only become more important.

When we see a majestic dam, with its huge face of concrete holding back acres of water, probably the last thing we think of are the valves it takes to make them operate effectively. But large dams, especially those providing hydroelectric power, are full of valves of all sizes and types. There are gates, globes, checks, balls and butterflies, along with some very special valve designs used only in the water reclamation industry.

 

To get an idea of the valving used in dams, we need to look at how dams work. Although we tend to think of them as structures designed to hold back water and create attractive recreational lakes, their true purpose is much more complicated. Dams are usually built to provide crucial water resources, and in more and more cases, their purpose is to ­provide renewable electrical energy.

 

vmsum12_dam_2A 156-inch butterfly valve is used to shut off flow into a large turbine.The purpose of the valves in these structures is to adjust the output of the reservoir that forms behind those dams while maintaining the proper reservoir depth, both in times of flood and in drought. Looking at the top of a moderate-size dam, we would see a number of rolling gates or sluices that provide the modulation of flow necessary to balance water supply and demand. In fact, the most common style of gate or valve used is a rolling type, which functions very similar to a sluice gate valve that is open at the top. Although this is technically a valve, these gates are not at all like the valve designs used in other industries.

All dams of substantial size need to have a way of releasing water in controlled amounts because of changing reservoir capacities, downstream water demands or minimum stream flow requirements. These situations call for special valves designed to dissipate the large amount of energy created by the high head of water in the dam.


WHAT VALVES ARE USED

At first glance, it might appear that ­virtually any type of shutoff valve would work, but a closer look at the operating conditions provides a broader picture. These outlet valves, which are releasing water, are doing so at huge volumes, ­relatively high head pressures and at a resulting high velocity. The combination of output flow conditions can result in severe damage from cavitation at the valve outlet. This phenomenon can ­rapidly destroy many types of valves, so measures to abate the cavitation must be taken either in valve selection or ­piping design.

Durivmsum12_dam_3Working on valves or piping within a dam environment sometimes calls for getting into tight spots.ng the early part of the 20th century, standard valve types such as gate and globe valves were given this flow control job. But the effects of cavitation destroyed them at an alarming rate. As a result, engineers looked at new valve designs, such as the Larner-Johnson needle valve, to solve the problem. Other solutions were also tried, included forcing air into the downstream flow of standard valve types to keep cavitation from occurring.

The needle valves, however, have done a good job for many decades, yet newer designs have now replaced many of those work horses. Both fixed-cone and jet-flow gate valve designs are now used in such applications and are ­currently being retrofit into existing structures as funds permit.

The fixed-cone, or Howell-Bunger valve, is a simple balanced design that requires little energy to open or close. The outlet of a fixed-cone valve is very similar to the outlet of a fireman’s hose nozzle or a high-end home garden hose nozzle, in that the high water pressure is squeezed around the periphery of the stationary cone by changing the position of the circular seat that is inset in the inside diameter of the moveable sleeve. The flow is regulated by adjusting the amount of water pressure introduced into the chamber behind the cone via a regulated water inlet.

The jet-flow gate valve looks like a large fabricated slab gate valve, similar to some API 6D designs. However, the secret to its energy-dissipating success is in the flow chamber of the valve. As designed, the slightly smaller inlet, with an inward taper just before the gate area, directs the mass of water into a narrow jet as the water exits the valve. The downstream port of the valve also flares out to avoid damage from the intense jet of water.

This design eliminates the possibility of cavitation damage. However, if the valve has a submerged outlet, a “stilling chamber” needs to be provided to dissipate the turbulent water flow and prevent scouring damage. A stilling chamber is a large pool of water sized to dissipate the output water energy without damage to the surrounding underwater landscape. If the jet-flow gate valve releases into the air, a structure-free zone needs to be provided for the length of the outlet stream.


  • Latest Post

  • Popular

  • Links

  • Events

Advertisement

Looking for a career in the Valve Industry?

ValveCareers Horiz

To learn more, watch the videos below or visit ValveCareers.com a special initiative of the Valve Manufacturers Association