Appliance Design - July 2008 - (Page 32)

MOTORS & PUMPS PRESSURE PRESSURE Flow vs. Altitude 4.0 4.0 3.5 3.5 3.0 3.0 2.5 2.5 2.0 2.0 1.5 1.5 1.0 1.0 0.5 0.5 0 0 10,000 10,000 Flow vs. Altitude VACUUM Flow vs. Altitude Flow vs. Altitude 5 psi 10psi 5 psi 20 psi 10 psi 20 psi Flow (cfm) Flow (cfm) VACUUM 3.0 3.0 2.5 2.5 2.0 2.0 1.5 1.5 1.0 1.0 0.5 0.5 5” Hg 5” Hg 10” Hg 10” Hg 15” Hg 15” Hg 20” Hg 20” Hg Flow (cfm) Flow (cfm) 50 psi 50 psi 100 psi 100 psi 7,500 7,500 5,000 5,000 Altitude (ft) Altitude (ft) 2,500 2,500 Sea Level Sea Level 0 0 10,000 10,000 7,500 7,500 5,000 5,000 Altitude (ft) Altitude (ft) 2,500 2,500 Sea Level Sea Level Fig. 5. Flow vs. altitude. Fig. 6. Flow vs. altitude. pressure or maximum vacuum required by the application. When determining this, be sure to take into account the maximum allowable pressure or vacuum tolerated by all devices in the system. In this case, look especially at connecting lines and hoses to be sure they are specified properly. Define the airflow requirement at the maximum working point. It is very important that the airflow requirement be tied to the highest pressure or vacuum required, as standard airflow ratings for pumps are usually “wide open” or “full flow” – meaning at zero pressure and zero vacuum. Manufacturers usually have performance curves showing pressures or vacu- um that can be delivered at various flows. Most applications do not require the maximum flow, pressure, or vacuum at all times, so define a typical working point and provide some idea of how frequently and for how long peak or maximum performance is required. This information can help prevent pump oversizing and potentially reduce cost. If stop and restart under pressure or vacuum is a requirement, be sure to note this. 2. Motor Requirements. Define the power source. If direct current (DC), specify the voltage and the source – for example, rectified AC, battery, solar, DC generator. If alternating current (AC), define the voltage as well as the frequency (generally 60 Hz in North America and 50 Hz in Europe and many other places in the world). List any power consumption and current draw limitations, and whether thermal overload protection is required. If the motor is to run at a constant speed, define how precisely must this speed be maintained. If variable flow through an adjustable-speed motor and controller is required, be sure to note that. Finally, determine the duty cycle of the application. Define it as either continuous or intermittent, and if the latter, indicate the pattern of minutes on/minutes off. 3. Unit Envelope. List height, width, and length maximums that can be accommodated, and determine how much free air space will exist around the unit. Knowing this will help the pump manufacturer determine whether there is sufficient cooling air, or whether additional fans or other cooling mechanisms will be required. Pump mounting must also be considered. www.applianceDESIGN.com 32 applianceDESIGN July 2008 http://www.elcomotors.com http://www.elcomotors.com http://www.appliancedesign.com

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Appliance Design - July 2008 Contents Editorial Shipments/Forecasts News Watch Heating Elements Gas Technology Motors & Pumps Controls & Sensors Design Marts Association Report: AHAM Advertiser's Index

Appliance Design - July 2008

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