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Valve Selection in Pulp and Paper Operations

Valve Selection in Pulp and Paper Operations

Over the centuries, the pulp and paper i...

How to Improve Control Valve Performance with Positioners

How to Improve Control Valve Performance with Positioners

As the final control element in most pro...

VMA Technical Event: Engineering Valves in the Extreme

VMA Technical Event: Engineering Valves in the Extreme

While much the 2017 VMA Technical Semina...

FEL: The Preferred Phase for Valve Technical Definition

FEL: The Preferred Phase for Valve Technical Definition

A typical oil and gas capital project cy...

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Industry Headlines

Kansas City Fed Shows Manufacturing At 6-Year High

Friday, 24 March 2017  |  Chris Guy

Tenth District manufacturing activity strengthened further in March, and many indexes of expectations for future activity were at or near record highs...

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Industry Headlines

GE Oil & Gas Expands with New Sub Saharan Africa Facility

1 DAY AGO

GE Oil & Gas opened a new facility in Takoradi Port, Ghana, expanding its global footprint and supporting local investment. The facility, which will be the primary service center for deep-water offshore projects in Ghana, has a 1,600 square meter indoor test area with capability for testing thre...

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Metso Launches Digital Program to Accelerate Growth

2 DAYS AGO

Metso has set up a Digital Program to accelerate the company’s digital capabilities, which are required to succeed in the future of minerals processing and flow control. Metso's ambition is to become one of the digital leaders in the industries it serves. This means for example turning custome...

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Shell Looking to Lower Cost of Offshore Projects

1 DAY AGO

“With oil prices hovering around $50 a barrel or less, and a rising amount of renewable energy chipping away at market share, Shell is going lean on its deepwater projects to make sure it can eke out a profit from all of its operations,” writes ChemInfo .

For example, Shell is attempting to ...

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Report Says PA Can Support Four More Ethane Crackers

1 DAY AGO

A new report from IHS Markit, commissioned by the state of Pennsylvania, forecasts $2.7 to 3.7 billion in investments in natural gas liquid (NGL) assets as well as the opportunity to attract additional cracker plants, and petrochemical and plastics manufacturing. IHS Markit believes the Marcellus an...

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Kansas City Fed Shows Manufacturing At 6-Year High

18 HOURS AGO

Tenth District manufacturing activity strengthened further in March, and many indexes of expectations for future activity were at or near record highs. Most price indexes increased moderately. The month-over-month composite index was 20 in March , its highest reading since March 2011, up from 14 in Fe...

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Consumer Sentiment Reaches Highest Level Since 2000

4 DAYS AGO

The overall level of consumer sentiment remained quite favorable in early March due to renewed strength in current economic conditions as well as the extraordinary influence of partisanship on economic prospects. The current economic conditions component reached its highest level since 2000, largely...

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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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