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Overflow Filling

Pressure overflow fillers deliver a quantity of free flowing liquid product into a container until the level reaches a specific fill level.

Although there may be slight variations in the sizes or shapes of bottles and jars, it is frequently desirable to have the fill line at the same height on each container so that all of them appear to be filled exactly the same when they are on the display shelf. Some manufacturers deliberately add extra product and overfill some of their “see through” containers in order to improve their appearance and to guarantee that all of them contain at least the minimum desired amount of product.

Molding and forming techniques can cause minor irregularities in the sizes or shapes of rigid glass and plastic bottles and jars, and some semi-rigid containers may also change their shape and volume slightly during the filling process. It is frequently more economical to use additional product in the oversized containers than it would be to more closely control the forming processes. Constant level filling techniques compensate for the minor changes and variations in the containers and produce the uniform appearance that is important in the sale of many products in ?see through? containers.

Fill to Level

• Pure gravity is not only one of the oldest and simplest constant level filling methods, but it is also one of the most accurate ones for filling free-flowing products. Accutek?s APOF fillers give you the option to eliminate the recirculation of the overflow product, and can hold aeration of the product to a minimum.

• Pure gravity filling can be used for most still liquids and some semi-solids. Products with consistencies as heavy as catsup or mustard can be filled in this way, but care must be taken with the heavier products to assure that the temperature and consistency of the product is maintained at a level at which the product flows freely and evenly. Although the constant level fillers can be adjusted to automatically operate at slower speeds when the product flows more slowly, this change in rate of flow can affect the timing of the conveying system and other machines in the packaging line.

• The product flow is produced in the pure gravity system by locating the product supply tank high enough so that the forces of gravity can be used to move the product through the feed mechanisms into the packaging line.

• The flow is started and stopped by the action of a spring loaded filling valve that is opened by the force of making contact with the top of the container. This is achieved by lowering the filler head down on the top of the container with a pneumatic powered diving head. When the pressure of the contact is sufficient, the spring opens the filling valve and the product flows from the supply tank into the container. The air and any foam that is formed through product filling turbulence in the container, is forced out through the vent tube or overflow port, as the product enters the container. The product will continue to fill the container and overflow through the overflow port until the diving head raises and the valve shuts. When the contact between the filler head and the container is broken the spring closes the filler valve and prevents dripping of the product as the head is removed from the container and positioned for the next fill. The amount of time the diving head is lowered and the valves remain open and the product viscosity determines the amount of product that is dispensed into the container.

• The fill level of the container is determined by the location of the overflow port in this tube within the neck of the container. When the product reaches the overflow port, the fill is completed, but the flow continues through the overflow tube until the seal on the container is broken and the valve sleeve covers the ports in the filling nozzle and stops the flow. The diving head must remain down and the valve open until liquid product is flowing from the overflow port to ensure that the proper liquid level is attained. The overflow is collected in the overflow tank and is then pumped back to the gravity tank or product bulk tank. This allows for no wasted product and a chance for any foam that is formed, to be condensed back to a usable liquid state.

• The maintenance requirements of the pure gravity filling system are relatively simple. The filler components must be kept clean and well lubricated, and the bearings, bushings, O-rings, and springs must be replaced when they wear excessively. The consistency of the product and the free movement of all moving parts are critical for smooth operation. Underfill may be caused by constriction of the Overflow Port by failure of sufficient product to move into the container during the time period it is under the filler head.

• The use of a gravity tank to provide product flow is the easiest and least expensive way to fill the product, but the gravity tank may be replaced with a pump. The use of a pump may increase product flow and therefor increase fill speeds. A centrifugal pump is the normal pump of choice due to it?s ability to pump against a ?dead head? without continuing to build up liquid pressure. If it is necessary to use a positive displacement pump, an air actuated valve must be placed on the output of the pump to cause a by-pass to ensure that liquid pressure does not exceed system capability and cause damage to the machine or the machine operator. It is also possible to use that same air signal to turn an air driven pump on or off when pressure is needed. The overflow product must now be pumped back to the product bulk tank to be recycled.

• The method that is used to keep the product from leaking out of the nozzle as it moves back and forth is the use of an O-ring. The O- rings are placed in grooves around the circumference of the nozzle tip as well as within the sliding nozzle body. There is a separate O-ring for the Fill Port and the Overflow Port. These rings may be made of a number of different materials that are selected to work best with the characteristics of the products being filled. Testing the chemical compatibility with the different types of elastomers is required to verify compatibility. The different elastomer that may be used is also dependent on the temperature range and abrasiveness of the product being filled. The different elastomers that are commonly used are:

• floroelastomers
• Buna
• Silicon
• Encapsulated Silicon
• Teflon

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