The Call: We received a call from a company using dry rotary claw vacuum pumps on their extruder vents. This company extrudes Polystyrene and ABS with a variety of extrusion equipment and had recently installed vacuum extruder vents on all of their extruders. Unfortunately they did not put vacuum traps in the line in front of the vacuum pumps to remove the volatile contaminants from the gas stream prior to the gas stream passing through the pumps. The simple, standard knockout pots installed in the line were not effective in removing the contamination from the gas stream.
The Result: This customer experienced a number vacuum pump failures due to this volatile material condensing in their pumps. This caused considerable extruder down time and costly vacuum pump repairs. We were contacted after their fourth vacuum pump failure.
The Fix: After reviewing this customer’s process in detail it was determined that installing an MV MULTI-TRAP with a Cooling Option in front of the vacuum pump would take the volatiles out of the gas stream so they would never make it to the vacuum pump. The right angle design trap that was deployed provided three types of traditional vacuum trapping including a cylindrical baffle knock down stage, a bottom cooling option with NPT drain plug, and a one stage of stainless steel gauze filters.
The Aftermath: Happiness in Extruderville! The traps tailored to this particular application have continued to remove volatiles from the gas stream and the customer has not experienced any vacuum pump failures whatsoever. The service schedule for this solution calls for the traps to be drained once a week and the filters changed every two months. In the end the cost of each trap was less than the cost to rebuild one of the vacuum pumps.
The Takeaway: There are very few extruder manufactures that offer a complete vacuum pump and trap package for extruder vents. Many offer recirculated liquid ring, oil lubricated rotary vane, and dry claw vacuum pumps. Simple knock out pots are usually provided by the extruder manufacturer or the vacuum pump manufacturer which, unfortunately, are not effective and can result in big-time vacuum pump failures. This is typically the point when we receive a call from the extrusion company looking for some help. If you are an extruder equipment manufacturer and have customers experiencing these types of problems or if you have an extrusion line and you want to avoid these problems you may want to consider an informal process review analysis to avoid some serious aggravation.
Comments: We are looking for real stories relating to vacuum technology and the problems you may have heard of or have encountered. The idea is to learn from the hard lessons of others, and maybe help others to avoid the same. Just like in “Drag Net” (for those of you old enough to remember “Drag Net,” and the rest of you can Google it) any names will be “changed ” to protect the innocent.