Simple Solutions That Work! Issue 10

magnets are certainly available, but the cost of the coupling often exceeds the cost of the pump, so it is important to size the magnet appropriately for the application Both direct and magnetically coupled style pumps are available in many different alloys as well to work with any specific resins that may be caustic. The most common for foundry use is Hastalloy, which is commonly used for Furan Resin Systems. VALVE TYPES On/off two-way valves – these are a simple air-actuated valve with an inlet and a discharge. These are commonly used with mixers to prevent backflow due to gravity when the gear pumps are not running. Recirculating three-way valves – these are an air-actuated valve that has one inlet and two discharges. These are commonly used with mixers where the pump is left running at all times that the mixer is powered, and the 57 valve simply diverts flow to the mixing chamber during mix cycles. When a mix cycle is finished, the resin will divert back through a recirculation line to the supply tank. Most new mixers being built now will have this steel-bodied style as the standard offering. PLUMBING RECOMMENDATIONS For an on/off type system, the sequence of components is usually: • Supply tank • On/off two-way valve • Pump • Mixer chemical nozzle For a recirculating type system, the sequence of components is usually: • Supply tank • Pump • Recirculating three-way valve • Mixer chemical nozzle – OR – Return line to supply tank Most foundry pumps are designed to push resins rather than pull them. For this reason, the best practices include: • Resin hoses feeding the pumps should be a larger diameter than the lines feeding from the pumps • Resin hoses should run downhill from the supply tank to the pump, with the pump being the lowest part of the system • Resin hoses should run uphill from the pumps to the recirculating valves, and continue uphill to the mixer chemical nozzle. The chemical nozzle should be the highest part of the system after the pump • Air bubbles are your enemy. Make as few joints in the lines as possible to avoid air bubbles, and always make the system easy to evacuate air bubbles from when found. Long runs of hard horizontal pipe should be avoided. If using long runs of hard pipe, try to arrange for it to run slightly uphill to avoid air bubble gathering. HOW TO Continued on next page