06272017Tue
Last updateTue, 27 Jun 2017 5pm

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Lubricants: Always Important—Sometimes Essential

Lubricants: Always Important—Sometimes Essential

Most valve professionals take more notic...

Why Air Valves are Needed in Water Applications

Why Air Valves are Needed in Water Applications

Air valves are hydromechanical devices d...

Achieving Profitability Through Maintenance Management

Achieving Profitability Through Maintenance Management

One of the distinctions between maintena...

Control Valve Positioner Performance Diagnostics

Control Valve Positioner Performance Diagnostics

There has been discussion for some years...

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Industry Headlines

Emerson in Talks to Acquire Software Company Paradigm Ltd.

1 HOUR AGO

According to Bloomberg , Emerson is in talks to acquire software company Paradigm Ltd. for approximately $1.5 billion.

“Paradigm specializes in seismic data interpretation and imaging equipment to help oil and gas companies know where to drill. The logic of such a deal seems sound and will help Eme...

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VMA Members Lead MDM Top Industrial PVF Distributors List

1 DAY AGO

Modern Distribution Management (MDM) recently published its Top Distributors list for 2017. Four of the top 5 distributors in the Industrial PVF category ; MRC Global, NOW Inc., Wolseley Industrial Group and FloWorks International; are currently VMA members.

“While oil & gas markets have start...

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Mountain Valley Pipeline Gets Environmental Approval

3 HOURS AGO

The Federal Energy Regulatory Commission (FERC) determined that construction and operation of the Mountain Valley Pipeline would result in some adverse environmental impacts, but the majority of these impacts would be reduced to less-than-significant levels. This determination is based on a review o...

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Delta Chemical Plant Planned for Houston Area

23 HOURS AGO

Braskem will commit up to $675 million in investment capital towards the design and construction of a new facility, named Delta, located next to Braskem's existing production facilities. Construction is expected to begin mid-summer, with the final phase of main construction targeted for the first qu...

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U.S. Durable Goods Orders Fell the Most in 18 Months

3 HOURS AGO

New orders for manufactured durable goods in May decreased $2.5 billion or 1.1% to $228.2 billion, the U.S. Department of Commerce announced. This decrease, down two consecutive months, followed a 0.9% April decrease. Excluding transportation, new orders increased 0.1%. Excluding defense, new orders...

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Texas Manufacturers See 12th Consecutive Month of Growth

4 HOURS AGO

Texas factory activity increased in June, according to the Texas Manufacturing Outlook Survey. The production index, a key measure of state manufacturing conditions, fell 11 points to 12.3, indicating output grew but at a slower pace than in May.

Other measures of current manufacturing activity also i...

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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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