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Vacuum – Nothing but Pressure

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Vacuum – Nothing but Pressure By Mike Tuohey, Sales & Marketing Communications Manager, Piab USA Inc. Vacuum – nothing but pressure According to the dictionary, vacuum is a space completely empty of substance. Yet, in engineering, vacuum is employed for a number of tasks. So, how can nothing be utilized to do something? Well, without pressure it wouldn’t work. Vacuum is an ideal and elusive state, and from a practical point of view it is perhaps not necessary to use this theoretical term, once a hot topic among philosophers in ancient Greece, especially since most modern thinkers agree that a complete or perfect vacuum does not exist. Even if all matter could be removed from a volume, it would still not be empty due to dark energy, rays, neutrinos and other phenomena in quantum physics. However, in particle physics, the vacuum state is considered the basic state of matter. In applied physics and engineering, on the other hand, it is probably more helpful to view vacuum as a negative pressure, as this is the force that can be harnessed to do work. The pressure controlled by a vacuum pump can be a powerful force. In a vacuum system, it is the differential between the atmospheric pressure and the vacuum (negative) pressure that creates the ability to lift, hold, move, and perform many types of work. Atmospheric pressure – the pressure we’re all under Atmospheric pressure is the pressure of the weight of the air above us. A cross section of a column of air, measured from sea level to the top of the atmosphere, would exert a pressure of approximately 14.7 pounds per square inch (psi). 1. Atmospheric pressure = 0 at an altitude of 621 miles. 2. 14.7 psi at sea level Psi is the pressure resulting from a force of one pound-force applied to an area of one square inch. The psi unit is still widely used in vacuum engineering, although Pascal (Pa) is the recognized SI unit. 1 psi is approximately 6,895 Pa. 1 Atmospheric pressure is the working force in all vacuum applications. Hence, the present barometric reading and the altitude above sea level must always be taken into consideration. As the altitude increases, the atmospheric pressure decreases, and so does the working force available for vacuum applications. At sea level the atmospheric pressure is 14.7 psi, while at 1,609 meters above sea level the atmospheric pressure will only be 12 psi. A practical implication of this is that a vacuum-lifting system that can hold almost 50 pounds at sea level can only hold 42 pounds at 1,609 meters. To fetch a pail of water An old fashioned, manually operated water well pump is an example of the ingenious use of negative pressure. As the handle is pumped it reduces the atmospheric air pressure inside the pump chamber. The pressure extends down into the well, and forces water up the pipe into the pump to balance the reduced pressure. Above-ground pump chambers are only effective to a depth of approximately nine meters due to the weight of the water column balancing the atmospheric pressure. Hence, in deep wells the pump chamber needs to be placed further down in the well, close to the water surface. The lung function of the person pumping the water provides another example of negative pressure in action. His or her diaphragm muscle expands the chest cavity, which causes the volume of the lungs to increase. This expansion reduces the pressure and creates negative pressure, which is soon balanced by air pushed in by atmospheric pressure. Measuring according to Torricelli, Pascal and Shaw The first example of man-made vacuum is usually attributed to Evangelista Torricelli, who in 1643 filled a glass tube with mercury and turned it upside down in a dish of mercury. Some of the mercury remained standing in the tube, held up by the weight of the surrounding atmospheric pressure. Torricelli had created the barometer, and alongside millimeters or inches of mercury (mm Hg or inHg), Torricelli (Torr) is still used as a unit with which vacuum or pressure is measured. Following in Torricelli’s footsteps, Blaise Pascal generalized and expanded the theory of pressure and vacuum. His name is used for another measuring unit (Pa), adopted by the International System of Units (SI) and defined as one newton per square meter (N/m2). Another familiar unit used for pressure is bar or mbar. This unit, metric but not SI, was introduced by the meteorologist William Napier Shaw in 1909. 1 bar equals 100 kPa. 2 The vacuum pump – a great invention Taking Torricelli’s and Pascal’s work a little further, Otto von Guericke invented the first vacuum pump in 1654. He demonstrated it by showing that teams of horses were unable to separate two hemispheres from which the air had been partially evacuated. Guericke’s design was improved by Robert Boyle and Robert Hooke, and their work further developed vacuum pump technology. In the mid-1800s, August Toepler invented the Toepler Pump and Heinrich Geissler invented the mercury displacement pump, achieving a partial vacuum of about 10 Pa. Perfect vacuum would measure 0 Pa, which would be a condition of total emptiness, a purely theoretical state. The lowest pressure currently achievable in a laboratory is about 13 pPa, although a pressure as low as 6.7 fPa has been indirectly measured in a cryogenic vacuum system. This corresponds to approximately 100 particles per cubic centimeter. Different types and areas of application Vacuum systems can be either sealed or open. In a sealed or nonporous system air is progressively removed, decreasing the air density within the confined space, creating negative pressure or a vacuum. To achieve negative pressure in an open or porous system, a vacuum unit must have the capacity to remove more atmosphere or air than the quantity that is able to leak back into the system. There are three main application areas for vacuum technology. Low-level vacuum applications are typically those requiring a high flow of air, such as ventilation, cooling and vacuum cleaning. Industrial vacuum applications include holding, lifting and moving of objects or materials. Scientific or process vacuum is used in laboratories, microchip manufacturing, ion implementation, and outer-space simulation. 3 Do you want more information about vacuum for industrial usage? Contact Piab About Piab Established in 1951, Piab designs innovative vacuum solutions that improve the energy- efficiency, productivity, and working environments of vacuum users around the world. As a reliable partner to many of the world's largest manufacturers, Piab develops and manufactures a complete line of vacuum pumps, vacuum accessories, vacuum conveyors and suction cups for a variety of automated material handling and factory automation processes. Piab utilizes COAX®, a completely new dimension in vacuum technology, in many of its original products and solutions. COAX® cartridges are smaller, more energy efficient and more reliable than conventional ejectors, and can be integrated directly into machinery. This allows for the design of a flexible, modular vacuum system. Piab is a worldwide organization with subsidiaries and distributors in almost 70 countries. Its headquarters are in Sweden. For more information about Piab vacuum solutions for a diverse range of applications, visit www.piab.com. 4 .
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