Fluid Handling

Poorly-performing valves are a pump system's weakest link

Don’t let control valves be a pumping system’s weakest link, advises Sheila Kennedy in this month's Technology Toolbox.

By Sheila Kennedy

Poorly performing or leaking valves are a source of frequent maintenance and costly repairs. They sacrifice pump efficiency, burn more energy, degrade plant output and can damage other equipment components.

The cost of preserving older valve designs may be greater than you think. New software tools can calculate the true life-cycle cost of valves and other components in your pump systems and compare alternatives for improving flow control. Advanced fluid handling technologies are dropping in price, further adding to the appeal of easy system redesign.

DOE assessment tools: U.S. Department of Energy (DOE) studies have found that pumping systems account for 25% to 50% of the energy consumed in certain industrial plant operations. The agency has published case studies that demonstrate how pump energy consumption can be reduced by as much as 20% with better system design and more effective pump applications.

Among the DOE pumping system tip sheets is the recommendation to conduct an in-plant survey on any pumping system with a larger than minimum size and those that exhibit significant operating hours. The DOE’s Pump System Energy Opportunity Screening worksheet helps to identify systems that merit a survey.

The DOE’s free Pumping System Assessment Tool (PSAT) also helps users to assess pumping system operating efficiency and to calculate potential energy and associated cost savings. The second edition of PSAT, released in June 2005, contains an updated valve tool.

HI modeling software: According to the Hydraulic Institute (HI), 90% of the total cost of owning a pump is energy consumption. HI’s Pump Systems Matter initiative seeks to draw attention to the total life-cycle cost of pump systems and highlight energy savings opportunities.

In addition to publishing pump guidelines and standards, HI offers a free Pump System Improvement Modeling Tool (PSIM). Plant professionals can use it to build models of pumping systems, simulate system behavior and calculate pump energy usage and cost as a function of time. PSIM modeling can shed light on the total costs associated with existing flow and pressure control systems. It also illustrates potential savings from upgrades and alternative technologies.

Valve upgrades: Rather than continuing to repair an existing valve, you might discover that a control valve replacement is more practical. Automatic valves and actuators are gaining favor. World Industrial Valves, a new industry research study by Freedonia, forecasts that global demand for automatic valves will outpace that for conventional control valves because of process manufacturers’ desire to improve efficiency.

Depending on your situation, it might be worthwhile to consider newer valves that provide both control and shutoff functions, protect against flashing damage, minimize cavitation, withstand the appropriate range of temperatures and pressure, and minimize noise and vibration.

Valves that aren’t insulated properly can be a source of heat loss. Removable and reusable insulating pads for pipes, valves and fittings can help minimize heat loss.

Valve alternatives: Achieving reliable, leak-free and maintenance-free flow control may involve eliminating the valve entirely. Throttled valves produce a considerable amount of pressure drop and are a major contributor to pump efficiency loss. Plants are increasingly recognizing the value of removing throttling valves in certain applications and replacing them with variable-speed pumps and smart motor control systems.

Smart pumps and motors can eliminate the need for valves, starters and bypass systems because the variable-frequency drives (VFDs) adjust pump speed automatically according to demand. VFD-controlled systems protect against process upsets and pressure spikes, and some have soft-starting capabilities. According to [i]PumpSmart[i], a 20% reduction in speed can reduce power consumption by 50%.

Also, consider replacing oversized pumps with two or more smaller units to avoid throttling a large pump during low demand.

E-mail Contributing Editor Sheila Kennedy, managing director of Additive Communications, at Sheila@addcomm.com.


Reference Web sites:

DOE industry software tools

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