Issue



Pumps in cleanroom processes


06/01/2007







Performance issues, such as reliability and efficiency, are the main consideration for pumps used in cleanroom applications

By Robert McIlvaine and Ann James, The McIlvaine Company

Pumps are used in a variety of industries involving cleanrooms: aseptic processing in the food and pharmaceutical industries, and ultrapure water applications in semiconductor, disk drive, and flat-panel display industries. Many changes are taking place in the pump industry to make pumps that fill the needs of cleanroom customers.

The main consideration of cleanroom pump customers is performance. For cleanrooms built to ISO Class 5-7 (Class 100-10,000), processing without contamination and on-stream reliability are the key factors. Cleanliness dictates that materials of construction for certain types of cleanroom applications must be PTFE, ETFE, PDFA, or metal lined with those materials. These non-metallic materials prevent the leaching of minerals from a metal pump by the ultrapure water. The material selected will also depend on the shape of the pump component; PTFE, for example, is often used for gasket material. Pumps that have seals also have to be at least lined with PTFE, PFA, or ETFE.

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Reliability is a very big issue because the users do not want to stop the cleanroom process to make repairs. For aseptic processing, the pumps are often put just outside the cleanroom to make repairing pumps easier. Also, in some cleanroom operations, the pumps are considered too noisy and dirty to be placed in the same room. The access to the pump room may be through a door in the floor or through a manhole from the platform atop the pump room. This location avoids having to cross the cleanroom to get to the pumps.


Figure 1. Main photo: A PFA-lined, magnetically driven, sealless pump for ultrapure liquids using a close-coupled motor. Inset: A disassembled version of the sealless pump, showing (left to right) casing with shaft and thrust ring, outer magnet with balance holes attached to motor, impeller with integrally attached inner magnet, mouth ring and bearing, and rear casing with thrust ring. (For video illustrating how this pump would be assembled, visit www.magnatexpumps.com
epair_guides.php.) Photos courtesy of Magnatex Pumps, Inc.
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Pumps are divided into three main categories: centrifugal, positive displacement, and vacuum. Four different types of pumps are often used in cleanrooms: centrifugal, air-operated diaphragm, vacuum, and metering. Centrifugal pumps are good for high flow rates at low pressures. Air-operated pumps are used for extra-pure and corrosive/abrasive service. Vacuum pumps are used when high temperature processing must be avoided, and metering pumps are used for precise flow measurements. Magnetic drive pumps and canned pumps have no seals to leak, so they are great for areas where leaks would cause a disastrous condition, but they are also quite costly.

Centrifugal pumps are either made of metal casings lined with PTFE or made of PTFE completely. The pumps can be sealed or sealless. Some are motor driven. Mike Clark, sales and marketing manager, at Magnatex Pumps, says, “The advantage of sealless pumps is that product does not escape across the mechanical seal faces as would be the case in a conventional pump. Even this small amount of contamination would likely be too much for the typical cleanroom application.” These pumps can be used for pumping any of the chemicals or deionized water used in cleanroom systems. They can run maintenance-free for 10 years or more.


Figure 2. A high-speed pump with low vibration and integrated drive electronics, such as the magnetically levitated HiMag 3400 shown here, is robust and suitable for industrial applications, coating processes, R&D, and the semiconductor industry, where particulate contamination, high gas loads, and corrosive gases are common. Photo courtesy of Pfeiffer Vacuum, Inc.
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Air-operated diaphragm or bellows pumps are also used to transfer ultrapure fluids in the semiconductor industry; recirculate, dispense, and filter with controlled flow rates and volumes; transfer chemicals and solvents in cleanrooms; and transfer and dispense corrosive chemicals, solvents, and pharmaceuticals. When using this type of pump to move deionized water, it will last much longer than when using it to move abrasive slurries. Ray Fas, product manager, Saint Gobain Performance Plastics, says, “To increase performance life, Saint Gobain sells a preventive maintenance kit to change the most affected parts during any kind of stoppage.” The wetted fluid path in these types of pumps is constructed entirely of high-purity materials such as PTFE.

Vacuum pumps have been made smaller over the years. They are used in all phases of semiconductor production. This type of pump is used in compound semiconductor applications, as well as silicon semiconductor fabs, supporting the production of devices such as LEDs, laser diodes, HEMTs, HBTs, MEMS, and optical waveguides.

Metering pumps are capable of dosing and proportioning a wide variety of materials including slurries and suspensions containing abrasive particles. What must be taken into account is the impact the material will have on the pump’s components. Metering pumps are used in a broad range of applications for single or multi-ingredient dosing. Single-point dosing typically involves the addition of a specific medium, such as a dye or chemical, accurately and in proper proportion on a continuous basis. Multiple liquid applications can be handled on a single multi-head machine, with the individual liquids metered independently to predetermined points in the process or brought together to create a blend.

While contamination issues and reliability are their main concerns, manufacturers are beginning to focus on operating efficiency and energy savings in the cleanroom industry. Some research has been done in this area by Dr. Tengfang Xu at Lawrence Berkeley National Laboratory. He reported on the benchmarked HVAC energy end use in a semiconductor cleanroom facility. The water pumps collectively accounted for 17 percent of the total energy use. Xu feels that the ability to lower water flow rate with a variable-speed drive motor while maintaining desirable water temperatures can significantly improve the energy efficiency of water pumps. As an example, a Western Digital factory in Malaysia set out to renovate an existing semiconductor manufacturing plant and incorporated a more energy-efficient design. We normally think that a more efficient design has higher first costs, but in the Western Digital case it led to lower costs for some sections. For example, due to low pressure drops through the air and chilled water systems, the efficient design required fewer and smaller pumps. The original system had pressure drops of around 100 feet, but the new layout was able to reduce that to about 35 feet. The new pumps were selected with minimum efficiency in excess of 70 percent and 92 percent efficient motors. The new vacuum pumps were 30 to 40 percent more efficient than the original plant. The new units used variable-speed drives to minimize power use during periods of off-peak processing loads when vacuum requirements are lower.

Cleanroom operators demand performance but now are recognizing that energy efficiency is becoming an important consideration. This example shows how the ever rising cost of producing and distributing electrical energy may justify high-efficiency pumps and motors for almost all applications. The higher initial investments in such pumping equipment may well pay off through lower operating costs. The continuous process industries will save a considerable amount of money and resources with better performing equipment.

Markets

Pumps in the electronics, food, and pharmaceutical industries are not only used in clean applications but also in the transport and treatment of incoming water as well as wastewater. They are also used to transport process liquids in non-clean areas of the plants. In the aggregate only 50 percent of the investment is for pumps for clean applications.

The market for cleanroom pumps will rise from $945.5 million in 2007 to approximately $1.156 billion in 2010. The food industry will be the largest purchaser followed by the pharmaceutical and then the electronics industries. Other applications include aerospace, medical devices, nanotechnology, and miscellaneous painting and other industrial applications where clean environments are required.

The revenues include both pumps and parts but only those sold by the pump manufacturers. They do not include parts sold by third parties. So a motor sold along with the pump as a package would be included. But a replacement motor sold directly by the motor manufacturer would not be included in the revenues.

The U.S. will remain the largest purchaser due to its strong position in the food and pharmaceutical industries. China is in a strong second place due to its rapidly growing process industries and, specifically, growth in electronics.


Robert McIlvaine is president and founder of The McIlvaine Company in Northfield, IL. The company first published Cleanrooms: World Markets in 1984 and has since continued to publish market and technical information for the cleanroom industry. He can be reached at rmcilvaine@mcilvainecompany.com.

Ann James is the pumps and valves market editor for The McIlvaine Company. She can be reached at ajames@mcilvainecompany.com.