In today’s down market, plastics processors are discovering a whole new set of problems related to operating at reduced capacity. Consider the case of an injection molder – a Conair customer – that has 40 injection-molding machines and, until recently, was operating around the clock. Today, with business down, they may run only 20 or 25 machines during the day and shut down entirely on weekends and sometimes during the third shift. They did not realize this posed a problem for their cooling system until they noticed the water pipes vibrating and swaying, especially when the system was starting up. Twice, this violent water-hammer effect caused joints in their water lines to rupture, flooding part of the plant and requiring plant downtime for clean up and repairs.
These problems arise from the fact that the pumps in a central cooling system are usually driven by fixed speed motors. If they are designed to deliver 700 gallons per minute (gpm), they will continue to try and pump 700 gpm even if several machines are shut down and only 500 gpm or less are flowing through the system. Unfortunately, all the energy that would normally go into moving the higher volume of water is converted instead into higher pressure and heat, wasting a lot of power and even potentially damaging system components. Also, when the system is restarted after a shutdown, the fixed speed pumps go from zero to full-speed almost instantly, driving large amounts of water through the lines at high pressure. This is when you see the pipes banging and swaying and when rigid joints can come apart. These are significant problems for many processors these days.