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From Cannon Balls to Pressure Seals: Graphite for Sealing

From Cannon Balls to Pressure Seals: Graphite for Sealing

From time to time, we re-publish well-re...

Gaskets Are Not Created Equal

Gaskets Are Not Created Equal

Gaskets are near the bottom of the food ...

Your Valves May Be Weaponized

Your Valves May Be Weaponized

The advent of the Internet of Things (Io...

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Industry Headlines

SVF Flow Controls Joins VMA

Friday, 22 June 2018  |  Chris Guy

This week SVF Flow Controls became a full member of the Valve Manufacturers Association (VMA). This is the fourth new VMA member in 2018 so far.

For over...

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Industry Headlines

SVF Flow Controls Joins VMA

-1 DAYS AGO

This week SVF Flow Controls became a full member of the Valve Manufacturers Association (VMA). This is the fourth new VMA member in 2018 so far.

For over 35 years SVF Flow Controls of La Palma, CA has been manufacturing ball valves, actuators and controls for all industrial applications.

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Emerson Wins Global Tank Storage Award

15 HOURS AGO

Emerson’s Rosemount 5900S 2-in-1 Radar Level Gauge has won the Outstanding Terminal Safety Technology Award at the 2018 Global Tank Storage Awards. This award is given to a product or technology that adds an additional layer of safety to the terminal and reduces risk to employees and the surroun...

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U.S. Specialty Chemicals Markets Continue to Gain

16 HOURS AGO

The American Chemistry Council (ACC) reported that U.S. specialty chemicals market volumes continued to gain during the second quarter, increasing 0.5% in May after an upwardly revised 1% gain in April and a 0.4% gain in March. All changes in the data are reported on a three-month moving average (3M...

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Global LNG Trade Growing, Led by Australia and the U.S.

1 DAY AGO

Global trade in liquefied natural gas (LNG) reached 38.2 billion cubic feet per day (Bcf/d) in 2017, a 10% (3.5 Bcf/d) increase from 2016 and the largest annual volume increase since 2010, according to the Annual Report on LNG trade by the International Association of Liquefied Natural Gas Importers...

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Optimism an All-Time High in NAM Survey

19 HOURS AGO

In the latest Manufacturers’ Outlook Survey from the National Association of Manufacturers (NAM), it’s clear that businesses continue to experience highly elevated levels of activity as a result of policies like tax reform, with optimism once again breaking records —95.1% of responde...

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Texas Economy Continues to Expand at “Solid Pace”

1 DAY AGO

The Texas economy is expanding at a solid pace. Employment has grown at a 3.6% annualized rate through May, driven by job gains in the goods-producing sector. Unemployment remains near its historical low, and labor markets are tight. The Dallas Fed’s Texas Business Outlook Surveys (TBOS) suggest...

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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.


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