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2.1.4 Pump selection The size and shape of the mold and type and quantity of the material being laminated will determine the minimum pump requirements. If you are laminating flat panels consisting of a few layers of glass, flat veneers or a core material, 5" or 6" Hg (2.5–3 psi) vacuum pressure will provide enough clamping pressure for a good bond between all of the layers. If the area of the panel is limited to a few square feet, a 1 or 2 CFM pump will be adequate to maintain that clamping pressure. As the panel area increases, the CFM requirement increases pro- portionately. A displacement of 3.5 CFM may be adequate for up to a 14' panel; for larger jobs, a pump with a displacement of 10 CFM or more may be required. Poor seals in the plumbing system or envelope, or material which allows air leakage, will require a larger ca- pacity pump to maintain satisfactory vacuum pressure. The more airtight the system, the smaller the pump you’ll need. A higher “Hg maximum” rated pump will be required if you need more clamping pressure to force laminations to conform to a more complex mold shape. Curved or compounded mold shapes and/or laminations of many layers of stiff veneers or core materials may re- quire at least a 20"–28" Hg vacuum to provide an adequate clamping force. Again, if the panel size is limited to a few square feet, a 1 or 2 CFM pump with a high “Hg rating” will work, if the envelope is airtight. However, a large panel or hull may take a minimum of 10 CFM pump to reach and maintain enough clamping force to press all of the laminate layers to the mold shape and produce consistent glue lines throughout the laminate. Generally, the best pump for a specific vacuum bagging operation will have the largest air moving ca- pacity for the vacuum/clamping pressure required while operating at a reasonable horsepower. 2.1.5 Pump types Vacuum pump types include piston, rotary vane, turbine, diaphragm and venturi. They may be of a positive or non-positive displacement type. Positive displacement vacuum pumps may be oil-lubricated or oil-less. Oil-lubricated pumps can run at higher vacuum pressures, are more efficient and last longer than oil-less pumps. Oil-less pumps, however, are cleaner, require less monitoring and maintenance, and easily generate vacuums in a range useful for vacuum bagging. Of the several types of positive displacement vacuum pumps useful for vacuum bagging, the reciprocating piston type and the rotary vane type are most common. Piston pumps are able to generate higher vacuums than rotary vane pumps, accompanied by higher noise levels and vibration. Ro- tary vane pumps may generate lower vacuums than piston pumps, but they offer several ad- vantages over piston pumps. While their vacuum ratings are more than adequate for most vacuum bagging, they are able to move more air for a given vacuum rating. In other words, they can remove air from the system more quickly and can tolerate more leaks in the system while maintaining a useful vacuum level. In addition, rotary vane pumps are generally more compact, run more smoothly, require less power and cost less. Figure 2-3 A Gast Model 07061-40, 1/8 hp diaphragm pump. This pump displaces 1.2 CFM and will achieve a maximum vacuum pressure of 24.0" Hg. It is a practical pump for small projects. Vacuum Bagging Equipment 5 2PDF Image | Vacuum Bagging Techniques 002150
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