International Appliance Manufacturing 2008 - (Page 15) again at the stroke’s top. The downstroke, of course, produces the reverse motion. In order both to guide the piston in the cylinder bore and to provide a seal (similar to piston rings) between the wobbling piston and the stationary cylinder walls, the piston rides within a flanged polymer cup. Air pressure on the upward stroke of a pressure pump or the downward stroke of a vacuum pump expands the cup against the cylinder wall, increasing its sealing properties while compensating for the wobble action. Made of a composite containing polytetrafluoroethylene (PTFE for short and most commonly known by the brand name Teflon), this cup produces a minimum of friction, requires no lubrication and generates relatively little heat. What Makes WOB-L So Popular: A WOB-L pump combines key features of a conventional piston pump (pressure, vacuum and flow performance) with key features of a diaphragm pump (compact size, quiet operation, clean airflow), and beats them both in efficiency and manufacturability. This combination has allowed WOB-L technology to capture a large – in some application areas, dominant – share of the pressure and vacuum market since its introduction just 30 years ago. Ongoing engineering enhancements have further opened applications to WOB-L pumps. These enhancements include: • Long-life sintered PTFE composite cups • Thin-wall aluminum housings for greater heat transfer • Anti-corrosion treatments to wetted pump parts for moisture tolerance • Stainless steel valves • Improved overall valve designs • Two-cylinder design, including a one-piece head version that provides fewer parts and reduced leak paths • Automated assembly processes for more consistent and quieter operation • Magnesium components for applications where extremely low weight is required • Variable-speed motors, including brushless DC for long life and, with the addition of closed-loop control, extremely precise speed regulation Where You’ll Find WOB-L Piston Pumps: The original WOB-L pump patent referred to the need to supply compressed air for applications “which are more or less mobile such as trucks, buses, mobile homes, etc.” While WOB-L pumps are certainly used in these applications, today’s application universe is, as one might expect, exponentially larger. Here’s a sample: Medical devices: Nebulizers, aspirators, oxygen concentrators, blood analyzers, blood pressure instruments, pneumatic hospital beds, emergency vehicle suction carts, dental carts, autoclaves and other sterilizers. Laboratory devices: Water aspirators, vacuum filters, dryers, mass spectrometers, electron microscopes, gas analyzers and samplers. Vehicles: Air-operated suspensions, seats, horns, clutches and doors. Vending machines for foods, drinks and compressed air. Business machines: Copy machines, mail sorters, vacuum frames. Environmental and safety devices: Air dryers, particle counters, ozone generators, dry fire sprinkler systems, floor cleaners. Telecommunications: Waveguide and other cable pressurization. Art and decoration: Airbrushes. Agriculture: Foam marking, air seats. Industry: Plasma cutters, plastic welders. Printing: Sheet transfer and separating, stitching and stapling. STEP 3: DOCUMENT THE APPLICATION PARAMETERS When coming up with a list of all the factors that might go in to specifying a WOB-L piston pump, it can be hard to know when to stop. The following “Top Ten List” should cover 90-plus percent of the information a pump manufacturer will need to know to recommend or design the best pump for your application: 1. Working Range Define the maximum pressure or maximum vacuum required by the International Appliance Manufacturing 2008 15
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