Selecting the Right Valve Type - Gate Valves

When it comes to controlling flow in an industrial fluid handling system, there are more choices than you can count. The journey of focusing in on the best option for your application can be shortened by employing some coarse filters to the vast array of available products and technologies, discarding choices that do not meet the basic criteria deemed essential to a successful project.

A common type of industrial valve is the gate valve. It regulates fluid flow by sliding a round or rectangular wedge, known as the gate or disc, in the flow path of the fluid. When the gate is fully retracted from the fluid path, flow is enabled to its fullest. Gate valves close by sliding the gate, which is commonly attached to a threaded shaft of other similar mechanism, into the path of the flow until it is fully obstructed. It is the movement of the gate, combined with the way in which a gate valve is constructed, that attributes this valve class with its positive and negative values.

Positives for gate valves:

• When fully open, there is low resistance to fluid flow. The opening in the valve tends to mimic the cross sectional characteristics of connected piping and fluid can flow through the valve without a directional change.
• Changing the gate position (opening or closing the valve) does not require as much force or power as some other valve types, due to the gate movement being perpendicular to the flow direction.
• Gate valves work in both directions. The flow in the connected line can be reversed and the valve function is unimpaired.
• The gate valve assembly tends to be shorter in length along the path of flow than some other designs.



Gate Valves in Process Pipeline

• The rate of closure is generally slow, providing a graduated reduction in fluid movement and reduced physical shock to the piping system.

Operating or construction characteristics that may be an advantage to gate valve employment on one application may prove a disadvantage in another.

“Not so positives” for gate valves:

• When the valve is open, the seals are exposed to the fluid flow. Foreign material, even elements of the process fluid, can deteriorate or contaminate the seals and impact the sealing of the valve when closed.
• The gate valve opens at a comparatively slow rate, making it unsuitable for applications that may require rapid or immediate shutoff.
• The service and maintenance space requirements, often extending overhead of the valve, can be substantial and may impact the ability to locate the assembly where desired.
• Gate valves are not well suited for throttling fluid flow. Fluid flow through a partially open valve of this type may cause the gate to vibrate.

There are certainly more elements involved in proper valve selection than are shown here, but this quick check may help you focus on gate valves or another technology for further consideration. It is always beneficial to bring in experts and those with experience to participate in the selection process.

Guided Wave Radar to Lower Power Plant Costs

Reducing costs at power plants.

For most power plant operators, fuel expenditures account for seventy to eighty percent of production costs and millions of dollars per year. In fact improving heat rate one percent could generate five hundred thousand dollars an annual savings for five hundred megawatt power point.

To contain fuel costs, power plants must maximize the efficiency of their feed water heaters. That's why many companies today are focusing on improving heat rate as a way to use their feed water heaters more effectively, and significantly reduce their fuel costs.

Guided wave radar
principle of operation.

Heat rate is a measure of how efficiently a power plant uses heat energy. You can measure heat rate by the number of BTU’s your plant requires to generate a kilowatt hour of energy. As you're heat rate goes up so do you're fuel costs.

The condenser is the beginning of the feed water heaters process, where condensed steam from the feed water heater drains, and HP, IP and LP turbines is routed through successive feed water heaters. At the same time,  extractions steam from your turbines reaches the appropriate feed water heaters and the transfer of energy takes place.

Maintaining accurate and reliable level control throughout this cycle is critical to achieving the final feed water heater temperature that your process requires.

Let's take a closer look at how this works.  Feed water heaters use the heat of condensation to preheat water to the correct temperature for the boiler. During this process, shell and tube heat exchangers allow feed water to pass through the tube side and extract steam from the turbine to the shell side.

The primary benefit of this process is that the feed water heater decreases the fuel costs by using recovered energy, rather than costly hot gas, to heat the water.

Achieving optimum water level in a feed water heater is a critical component of maximizing energy transfer and minimizing controllable losses.

There are normally six to seven stages of feed water heating. Making an investment in level control can help you achieve optimum heat transfer and improved terminal temperature difference to provide a significant return on investment.

Guided wave radar
transmitter
(courtesy of
Magnetrol)

With a guided wave radar level control, you can optimize the condensing zone of your feed water heater to deliver accurate level control, maximize energy transfer, and minimize undue wear and tear. This can help you generate the savings needed to recover your investment.

Older level technologies, such as differential pressure, magnetostrictive, or RF capacitance and torque tubes are vulnerable to process conditions and induced instrument errors, such as shifts in specific gravity and mechanical or electronic drift.

In contrast, guided wave radar provides a truly reliable level measurement solution for feed water heaters. Guided wave radar performance is virtually unaffected by process variations and gives you a superior degree of accurate and reliable continuous level measurement without the need for calibration or gravity corrections.

With superior signal performance and advanced diagnostics, guided wave radar delivers premier level control for feed water heaters, as well as a broad range of challenging applications, such as condenser hot wells, deaerators, and cooling tower basins.

Combining a magnetic level indicator with guided wave radar merges the operating systems of a conventional flowed base magnetic level indicator with a leading edge solution. This allows you to effectively measure low dielectric media, high temperature, and high pressure process conditions and media, with shifting specific gravity and dielectric values accurately and repeatedly. The result is a diverse and redundant level measurement solution in a single chamber design.

For more information contact:

M.S. Jacobs and Associates
Phone: 800-348-0089
Fax: 412-279-4810
Email: msjacobs@msjacobs.com
www.msjacobs.com