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Technical

Valves in a Cement Slurry Line

Basically everywhere you look in modern society, you see something made of concrete. Often we see trucks traveling down the road, drums spinning to keep the cargo mixing on their way to a job site in a subdivision or business park. It’s so common, in fact, that most people barely give it a second thought, but the process that turns limestone into towers of concrete and steel is one that creates its own challenges for valves in a cement plant, especially those in the slurry line.

One of the largest cement companies in the world is Lafarge, which produces cement for residential and commercial construction and for oil wells. Ed Kunkel worked for Lafarge at its plant in southwestern Ontario for more than 30 years, and he provided much of the process line and valve specification information for this article. We also spoke Ed Holtgraver of QTRCO, Inc., Tomball, TX, who provided us with additional information about valves and actuation.


Digital Valve Control Leads to Increased Plant Availability

Surge is characterized by fast flow reversals through a compressor and is caused by a large-scale breakdown of flow patterns within the compressor. Surge happens at low flow rates, often when the downstream demand decreases. When flow decreases below a certain minimum point, flow patterns in the compressor become unstable and fluid can move back through the compressor from the high-pressure side to the low-pressure side.

Because surge is a fast, high energy phenomenon, it can introduce excessive dynamic loads on internal components, such as thrust bearings, seals and blades as well as introduce unwanted pipeline vibrations. The cost of replacing compressor seals alone is on the order of $20K to $50K. Over time, surge can introduce fatigue failures that can damage the entire compressor.

Warriors, Welding and Wooing the Workforce

For the last several years, one of the biggest concerns voiced by manufacturers, construction firms, refiners, petrochemical and petroleum producers is the shortage of skilled manpower. In fact, it could be said that employers in these sectors are weathering the perfect storm of circumstances: Experienced baby boomers are reaching the age of 65 at the rate of 10,000 per day and a good percentage of them are retiring shortly thereafter, manufacturing has a reputation in recent years as being a dumb, dirty and dangerous career option, and changes brought about by digital and technological changes in all facets of industry are taxing those who are in the field. Recruiting, training and retaining quality skilled people is proving difficult even for the most forward-thinking companies.

Avoid Water Hammer Problems in High-Pressure Hydraulic Systems

Water hammer, high-velocity fluid flow and contaminated hydraulic media are among the worst enemies of high-pressure hydraulic systems. Water hammer, in particular, can be very destructive in high-pressure descaling applications. At steel mills, persistent water hammer in high-pressure piping systems often leads to burst pipes, cracked welds and descale header damage. In some cases, control valves have actually exploded due to water hammer.

The Critical Stem Nut: Who is Responsible for Maintenance?

One of the most important components of an automated threaded stem valve is the ubiquitous stem nut, a relatively simple and unsophisticated mechanical device that converts the rotary motion of an actuator into the linear stem movement needed to open or close one of the many types of gate valves or sluice gates.

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