See Vacuum being drawn Graphic courtesy of R. A. Jones & Co. See Boyle's Law PV = Constant April 2013 Spray 27 See Bag-On-Valve Rolled & Taped See Bag-On-Valve in Container Container Seal sealed to Can Dome See Cup Grip grip Valve Cup Seal gripping Mounting Cup Skirt Graphic courtesy of R. A. Jones & Co. See U-T-C Gasser Fill Container Graphic courtesy of R. A. Jones & Co. Cup Seal gripping Mounting Cup Skirt and holding Valve above Can Bead to allow for Propellant Fill into the can. 200 180 160 140 120 100 80 60 40 20 0 1.00 0.95 0.90 0.85 0.80 0.75 0.70 0.65 0.60 0.55 0.50 0.45 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 Container Pressure Bag Empty - Container Volume minus Contents of Bag - Bag Full Most BOV products are designed to utilize compressed gases as propellants. However, liquefied propellants can be used and, indeed, do provide some product benefits over compressed gases. For instance, liquefied propellants will provide a constant pressure over the life of the product. The straight line on the Boyle’s Law graph illustrates the constant vapor pressure resulting from the use of a liquefied gas. The pressure in the unit when the container is almost empty will be the pressure that the unit was initially pressurized to via UTC gassing. The pressure in the unit when the bag is filled can be approximated using Boyle’s Law. Pressure regimes can be altered by varying the bag volume relative to the can volume using Boyle’s Law as a reference. The bag must be rolled and taped or it will not fit into a 1" container opening. Once the valve and bag assembly is placed in the container, it does not tend to jump out as it progresses down an aerosol line, but stays put. The weight of the bag will hold it in place in the can, reducing or eliminating the need for dimples. This shows the vacuum being drawn. The bag is sealed onto the valve and dropped into the can. Then a vacuum is drawn through the valve that removes all air and leaves no contamination. This step is optional, as most BOV products on the market today use nitrogen or air as the propellant. Engineering drawings are courtesy of R.A Jones & Co. The product is filled backwards through the valve into the bag. As the product fills the bag the volume outside the bag in the can is reduced. If a compressed gas is used the pressure in the can rises following Boyle’s Law. If a liquefied propellant is used the pressure in the can remains essentially constant. The bag should be sized such that the inside width of the empty bag is slightly wider than one half of the can circumference so that when the bag is full it will press snuggly against the inside side wall of the can to provide some stability to the bag. The valve is in the container and the bag should be long enough to reach the top of the can dome in order to maximize product volume. The cup seal will grab the valve by the skirt of the mounting cup and lift the valve off of the can bead to maintain a path for propellant flow into the can. The collet will then come down and crimp the mounting cup resulting in a pressurized container.
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