again to fig1 2 3 and 13 vacuum pump 34 is preferably a positive displacement type vacuum pump in one preferred embodiment vacuum pump 34 is a model 49urai dsl blower manufactured by roots blower division of dresser roots of texas vacuum pump 34 has a low pressure intake port 170 and a high pressure outlet port 172 fitted with a silencer 174 that reduces the noise associated with the air forced out of the vacuum pump outlet port silencer 174 may be a model ts30tr cowl silencer manufactured by phillips and temro industries of canada vacuum pump intake port 170 is fitted with a vacuum relief device 176 which may be any suitable vacuum valve such as a model 215v h01aqe spring loaded valve manufactured by kunkle valve division black mountain n c vacuum relief device 176 controls the maximum negative pressure of the vacuum pulled by pump 34 which is in the range of between 10 and 15 inches of mercury hg in the illustrated embodiment referring to fig1 a blower pipe 178 connects vacuum relief device 176 with an air filter 180 located upstream of pressure relief device 176 that filters the vacuum air stream before it passes through vacuum pump 34 in one preferred embodiment the filter media.