Trucking Up History: The Science of Pneumatic Hauling

1 00:00:00,280 --> 00:00:06,200 How's it going out there? Bulk and Spur. Welcome into a very special presentation of trucking up 2 00:00:06,200 --> 00:00:12,600 history presented by Bulk Transit. Now, on today's show, we will bring you a documentary 3 00:00:12,600 --> 00:00:19,119 style episode that talks about the comprehensive history and science behind the 4 00:00:19,120 --> 00:00:25,680 pneumatic trailer. So check your airlines and top off the tank as we jump in to this episode of 5 00:00:25,680 --> 00:00:32,560 Trucking Up History. You are listening to Always Pneumatic, Never Static, 6 00:00:32,600 --> 00:00:37,880 the Totally Pressurized podcast brought to you by Bulk Transit, where we keep the lines clear, the 7 00:00:37,880 --> 00:00:43,200 tanks empty, and the conversation anything but dry. Whether you're running powder pellets or anything 8 00:00:43,200 --> 00:00:47,120 in between. Pull up a seat, crack the windows, and let's hit it. 9 00:00:50,600 --> 00:00:56,720 There are machines that look complicated, and then there are machines that hide their complexity 10 00:00:56,760 --> 00:01:03,709 remarkably well. A pneumatic trailer belongs firmly in that second category. Look 11 00:01:03,750 --> 00:01:09,269 at one sitting in a yard. At a first glance, there isn't much mystery to it. You've got a big 12 00:01:09,269 --> 00:01:15,829 aluminum vessel, a few cones underneath it, pipes, valves, hoses, a blower hooked to a 13 00:01:15,830 --> 00:01:22,509 truck, put dry product in the top. Connect a hose at the customer, turn on the air. Product comes 14 00:01:22,510 --> 00:01:29,349 out simple. Except it isn't, because inside that trailer you're asking air to do 15 00:01:29,349 --> 00:01:35,470 something that seems almost ridiculous when you really think about it. You're asking air to move 16 00:01:35,470 --> 00:01:42,230 tons of solid material through a pipe cement, flour, limestone, fly ash, 17 00:01:42,269 --> 00:01:49,029 plastic pellets, powdered chemicals, feed ingredients. Products that normally sit obediently 18 00:01:49,030 --> 00:01:55,910 in a pile suddenly begin behaving almost like a liquid. They move down through the trailer, enter a 19 00:01:55,910 --> 00:02:02,449 pipe, and travel through bends, hoses and vertical runs until they arrive inside a silo that might 20 00:02:02,489 --> 00:02:08,649 tower dozens of feet above the truck. There's no conveyor belt running that hose. There's no auger 21 00:02:08,649 --> 00:02:14,929 reaching from the trailer to the silo. There isn't a pump pushing liquid. There is air, 22 00:02:15,009 --> 00:02:21,809 and behind that air is more than a century of engineering. Actually, the story 23 00:02:21,809 --> 00:02:28,689 begins even earlier than that. Because before anybody built a pneumatic trailer, engineers first 24 00:02:28,689 --> 00:02:35,209 had to discover that air could be used to transport solids at all. And that story takes us 25 00:02:35,210 --> 00:02:42,049 back to the middle of the 19th century. Chapter one. When air learned to 26 00:02:42,089 --> 00:02:48,249 move things, human beings understood compressed air. Long before they understood, pneumatic 27 00:02:48,249 --> 00:02:54,529 conveying bellows had been used for centuries. Vacuum pumps appeared in Europe in the 28 00:02:54,529 --> 00:03:01,479 1600s. Compressors continued developing through the 18th and 19th centuries, but moving a 29 00:03:01,480 --> 00:03:08,160 solid material through a pipe using air was a different problem entirely. One historical review, 30 00:03:08,160 --> 00:03:14,639 published in KKona Power and Particle journal traces documented industrial pneumatic conveying 31 00:03:14,640 --> 00:03:21,490 back to the mid 1800s. Grain was reportedly pneumatically unloaded from ships between 32 00:03:21,490 --> 00:03:28,440 1856 and 1876, in ports including London, Rotterdam, Hamburg and what 33 00:03:28,440 --> 00:03:35,279 was then Saint Petersburg or later Leningrad. An image from 1882 shows grain being 34 00:03:35,280 --> 00:03:41,679 handled pneumatically aboard a Russian ship. Think about what problem those early systems were 35 00:03:41,680 --> 00:03:48,440 trying to solve. A ship arrives carrying grain. Grain is very heavy. There is 36 00:03:48,440 --> 00:03:54,959 an enormous amount of it, and somebody has to get it out of the ship. The traditional answer 37 00:03:54,960 --> 00:04:00,710 involved manpower and mechanical handling equipment. But what if you could essentially build 38 00:04:00,710 --> 00:04:07,070 an enormous vacuum cleaner? Put a pipe into that grain, move enough air through that pipe, and 39 00:04:07,070 --> 00:04:13,390 suddenly individual kernels of grain become passengers in an airstream. One 40 00:04:13,390 --> 00:04:20,229 technological development helped make that idea increasingly practical. In 1859, 41 00:04:20,230 --> 00:04:26,389 brothers Philander and Francis Rootes patented what became known as the roots blower. 42 00:04:27,230 --> 00:04:32,669 The roots blower is important to our story because descendants of that basic positive 43 00:04:32,670 --> 00:04:39,109 displacement blower concept remain familiar equipment in pneumatic conveying. Today, the 44 00:04:39,109 --> 00:04:43,429 historical review from the University of Pittsburgh's George Cleansing identifies 45 00:04:43,429 --> 00:04:49,589 development of the roots blower as a major turning point in pneumatic conveying. The blower 46 00:04:49,589 --> 00:04:56,328 does something extremely useful. Instead of merely stirring air around it can move a substantial 47 00:04:56,329 --> 00:05:02,129 volume of air and create a pressure difference. And pressure difference is the beginning of our 48 00:05:02,129 --> 00:05:08,609 story. But it isn't the whole story. Because here's our first important piece of pneumatic 49 00:05:08,649 --> 00:05:14,209 trailer science. Pressure does not magically push the product through the hose. 50 00:05:14,570 --> 00:05:21,529 Ultimately, the product moves because flowing air exerts force on particles. The 51 00:05:21,530 --> 00:05:27,529 American Institute of Chemical Engineers explains that the critical physical mechanism is drag 52 00:05:27,530 --> 00:05:34,369 force. Gas moving relative to a particle exerts force on that particle, and that force 53 00:05:34,369 --> 00:05:41,249 depends on factors including gas density, particle size, and shape, and especially the relative 54 00:05:41,249 --> 00:05:48,209 velocity of the air. That's why you can blow a speck of flour across a countertop much more 55 00:05:48,209 --> 00:05:54,839 easily than you can blow a rock across the same countertop. The air is interacting with both, but 56 00:05:54,839 --> 00:06:01,639 the particles are very different, and that simple fact becomes incredibly important later, because a 57 00:06:01,640 --> 00:06:07,479 pneumatic system that handles flower beautifully may behave very differently with pellets, cement, 58 00:06:07,480 --> 00:06:12,879 or another mineral product. The material matters a lot. 59 00:06:14,480 --> 00:06:21,279 Chapter two. From grain to coal to cement. By the early 20th century, engineers were 60 00:06:21,280 --> 00:06:26,759 beginning to seriously study what happened when solids and air traveled together through pipes. 61 00:06:27,280 --> 00:06:34,040 Research in Germany in 1924 examined pressure drop and solids flow in pneumatic conveying 62 00:06:34,040 --> 00:06:39,799 systems. According to the historical review of the field, this was among the earliest formal 63 00:06:39,799 --> 00:06:45,440 technical investigations of pneumatic conveying behavior. But another major development was 64 00:06:45,440 --> 00:06:51,540 already happening in American industry, and it involved something far more dangerous than grain. 65 00:06:52,019 --> 00:06:59,019 Pulverized coal. Coal could be ground down into a fine powder and used efficiently as fuel, but 66 00:06:59,019 --> 00:07:05,500 moving that powder mechanically created serious problems. Dust. 67 00:07:05,540 --> 00:07:12,220 Fire. Explosion hazards. An engineer named Alonzo G. Kenyon, working with the 68 00:07:12,220 --> 00:07:17,459 Fuller Lehigh Company, developed a machine specifically intended to pneumatically convey 69 00:07:17,459 --> 00:07:23,979 pulverized material. The first prototype of what became the Fuller Kenyon pump was built around 70 00:07:23,980 --> 00:07:30,699 1918, with the design adopted the following year. The modern manufacturer traces the original 71 00:07:30,700 --> 00:07:37,099 design to 1919, and says it was developed specifically in response to the hazards involved 72 00:07:37,099 --> 00:07:43,700 in moving pulverized fuel. The idea was enormously important. Instead of dragging 73 00:07:43,700 --> 00:07:49,738 powder around a plant on exposed mechanical conveyors. Engineers could move material through 74 00:07:49,769 --> 00:07:56,289 enclosed pipes. The Fuller Kenyon system mixed pulverized material with air so that the 75 00:07:56,289 --> 00:08:02,768 material entered a fluidized condition and could be conveyed through piping and cement. 76 00:08:02,769 --> 00:08:08,689 Manufacturers quickly recognized the possibilities. That matters because cement would 77 00:08:08,690 --> 00:08:13,450 eventually become one of the forces that push pneumatic technology out of the stationary 78 00:08:13,489 --> 00:08:19,930 factory and onto the highway. The Hoover Dam provides an early example of just how useful 79 00:08:19,969 --> 00:08:26,889 pneumatic handling had become during construction of the dam. Enormous quantities of cement had to 80 00:08:26,890 --> 00:08:33,369 be received and moved into storage. Fuller Kenyon pumps were used to unload and convey cement into 81 00:08:33,409 --> 00:08:39,089 storage silos at the project's blending plant. We're still not talking about the pneumatic 82 00:08:39,090 --> 00:08:45,968 highway trailer we recognize today, but most of its DNA is now present dry powder, 83 00:08:45,969 --> 00:08:52,799 compressed air, a closed vessel, A pipeline and a storage silo. And the realization 84 00:08:52,800 --> 00:08:59,039 that under the right conditions, powder doesn't necessarily have to be carried mechanically. It 85 00:08:59,040 --> 00:09:05,719 can flow. Chapter three how do you make a solid act like a 86 00:09:05,719 --> 00:09:12,400 liquid? This is where pneumatic trailers start becoming genuinely strange. Take flour. 87 00:09:12,559 --> 00:09:19,359 Dump a pile of flour on a table. It doesn't flow like water. Take cement. Same thing. Take 88 00:09:19,360 --> 00:09:26,119 fine limestone, same thing. These are solid materials. Every individual particle 89 00:09:26,119 --> 00:09:32,959 obeys the laws of solid mechanics. But introduce air into a bed of sufficiently fine particles in 90 00:09:32,960 --> 00:09:39,199 the right way. And something fascinating begins happening. The particles separate slightly from 91 00:09:39,200 --> 00:09:45,039 one another. Friction between neighboring particles decreases. The bulk material becomes 92 00:09:45,039 --> 00:09:51,819 easier to move. Engineers call this process fluidized. It doesn't mean the material 93 00:09:51,859 --> 00:09:58,219 literally becomes a liquid. The particles are still solid, but collectively the bed can begin 94 00:09:58,219 --> 00:10:04,259 exhibiting liquid like behavior. This is why aeration is such an important part of many 95 00:10:04,259 --> 00:10:10,699 pneumatic trailer designs. Air introduced around the bottom of a hopper helps loosen the product 96 00:10:10,700 --> 00:10:17,699 and encourage it towards the discharge outlet. Historically, fabric aeration media were widely 97 00:10:17,699 --> 00:10:24,218 used. Air passed through the porous fabric into the powder above it. Later designs introduced 98 00:10:24,219 --> 00:10:29,658 different types of aerators or fluid risers, intended to reduce clogging and maintenance 99 00:10:29,659 --> 00:10:36,659 problems associated with the fabric media. And now the shape of the trailer begins to make some 100 00:10:36,659 --> 00:10:41,978 sense. Those cones underneath a pneumatic trailer aren't there because somebody thought they looked 101 00:10:41,979 --> 00:10:48,968 cool. Gravity is working alongside the pneumatic system. The sloped walls encouraged material 102 00:10:49,010 --> 00:10:55,489 towards the bottom outlet. Aeration helps the material flow. Pressure inside the vessel helps 103 00:10:55,489 --> 00:11:02,249 establish the conditions for discharge. Then the conveying air helps carry the material through 104 00:11:02,249 --> 00:11:09,089 the discharge line. In other words, the trailer is using several forces at once. Gravity 105 00:11:09,090 --> 00:11:15,609 gets the product towards the outlet. Aeration helps the bulk material flow. Pressure establishes 106 00:11:15,610 --> 00:11:20,809 the driving conditions, and moving air transfers the momentum to the particles and carries 107 00:11:20,809 --> 00:11:26,450 material through the line. A modern pneumatic unloading system is basically a carefully 108 00:11:26,450 --> 00:11:32,449 controlled argument between gravity, friction, pressure, and air flow, and if those forces 109 00:11:32,449 --> 00:11:39,329 cooperate. Unloading can look effortless when they don't cooperate, well, that's where the drivers 110 00:11:39,329 --> 00:11:44,959 earn their money. Chapter four The road to the modern Pneumatic trailer. 111 00:11:46,119 --> 00:11:52,679 Dry bulk trucking existed before pneumatic. Trailers, and especially valuable 112 00:11:52,719 --> 00:11:58,679 historical snapshot comes from a 1961 technical paper discussing pneumatic truck 113 00:11:58,680 --> 00:12:05,200 transportation. According to that account, bulk dry products had already been transported by truck in 114 00:12:05,200 --> 00:12:11,280 the United States for more than 30 years. Early systems included dump trucks and gravity 115 00:12:11,320 --> 00:12:17,840 discharge hoppers. During World War two and the postwar period, another popular trailer designed 116 00:12:17,840 --> 00:12:22,599 use an auger to move material toward the rear of the trailer, where it could be discharged into a 117 00:12:22,599 --> 00:12:29,439 customer's receiving hopper belt. Trailers offered another solution, and another design used 118 00:12:29,440 --> 00:12:35,039 low pressure air to fuze through porous fabric to help aerate dry material and encourage it towards 119 00:12:35,040 --> 00:12:41,399 the discharge. Then somebody combined those ideas with pressure vessel technology. 120 00:12:42,159 --> 00:12:48,779 The 1961 account points to the oil well cementing industry as an important ancestor of the highway 121 00:12:48,820 --> 00:12:55,499 pneumatic trailer. Small pressure vessels were used to transport bulk cement inside those early 122 00:12:55,499 --> 00:13:01,339 vessels. Aeration helped fluid ize the cement. The vessel could be tilted so the material moved down 123 00:13:01,340 --> 00:13:08,219 a relatively shallow slope toward a discharge point. Additional air was mixed with the cement so 124 00:13:08,219 --> 00:13:14,619 it could then travel through hose or pipe. There it is, the basic pneumatic trailer 125 00:13:14,620 --> 00:13:21,339 concept, except early versions were relatively small, so engineers started making them bigger. 126 00:13:21,780 --> 00:13:28,460 One step was joining vessels into a double tapered tank, feeding a common outlet. Then 127 00:13:28,460 --> 00:13:34,059 designers pursued configurations with multiple steep sided hoppers connected to a common 128 00:13:34,059 --> 00:13:40,739 discharge pipe. A Swiss patent with priority dating to 1954, 129 00:13:40,780 --> 00:13:46,449 describes a truck for carrying loose bolt goods and unloading them pneumatically, demonstrating 130 00:13:46,450 --> 00:13:52,489 how actively engineers were pursuing mobile pneumatic bulk transportation during this period. 131 00:13:52,489 --> 00:13:59,129 And then came the late 1950s. That's when pneumatic dry bulk trucking really 132 00:13:59,130 --> 00:14:06,089 began taking off in the United States. Chapter 51958. When the 133 00:14:06,090 --> 00:14:12,808 market catches up with the machine, technology doesn't spread simply because it works. It 134 00:14:12,809 --> 00:14:19,529 spreads when economics give people a reason to use it. For pneumatic trucking, cement provided 135 00:14:19,530 --> 00:14:26,369 that reason. The 1961 Butler Manufacturing paper identifies late 1958 as a 136 00:14:26,369 --> 00:14:32,770 turning point. American cement producers were facing excess production capacity and competition 137 00:14:32,770 --> 00:14:38,929 from imported cement. Distribution became increasingly important, and trucking offered 138 00:14:38,930 --> 00:14:45,709 manufacturers Flexibility. Pneumatic delivery offered something especially attractive. The 139 00:14:45,710 --> 00:14:52,229 trailer wasn't merely transportation. It was also part of the customer's material handling system. 140 00:14:52,669 --> 00:14:57,870 The truck could arrive, connect to the customer's piping, and transfer its load directly into 141 00:14:57,909 --> 00:15:04,749 storage. No bags. No army of workers unloading sacks. No separate portable 142 00:15:04,749 --> 00:15:11,109 conveyor required to get material from the truck into the silo. The truck had effectively become a 143 00:15:11,109 --> 00:15:17,390 shipping container with its own unloading system. According to the Butler paper, demand 144 00:15:17,390 --> 00:15:22,390 accelerated dramatically and a variety of pressure unloading trailer designs appeared on 145 00:15:22,390 --> 00:15:28,989 the market beginning around 1959. Government labor statistics showed just how dramatically cement 146 00:15:28,990 --> 00:15:35,630 distribution itself was changing. In 1958, approximately 79% of Portland 147 00:15:35,630 --> 00:15:42,259 cement shipments were already being made in bulk. By 1964, that figure had climbed above 148 00:15:42,260 --> 00:15:49,259 87%, and by 1961, trucks had overtaken other modes as the dominant means 149 00:15:49,259 --> 00:15:55,819 of shipping Portland cement. In 1964, trucks accounted for roughly 66% of 150 00:15:55,820 --> 00:16:01,980 shipments. The US Bureau of Labor Statistics specifically credited pneumatic handling with 151 00:16:01,980 --> 00:16:07,658 helping make increased bulk shipment possible, while reducing manual labor associated with 152 00:16:07,659 --> 00:16:14,459 unloading and loading. The Interstate Highway System was simultaneously expanding. The 153 00:16:14,460 --> 00:16:20,579 Federal Aid Highway Act of 1956 helped unleash one of the largest road building programs in 154 00:16:20,580 --> 00:16:27,339 American history. Roads needed concrete. Concrete needed. Cement and cement needed. 155 00:16:27,380 --> 00:16:34,299 Transportation company specializing in bulk hauling grew rapidly during this era. Sherman 156 00:16:34,300 --> 00:16:40,049 Trucking, for example, expanded aggressively during the 1950s, as construction and highway development 157 00:16:40,049 --> 00:16:45,409 increased demand for cement transportation, the company became an early user of dry bulk 158 00:16:45,409 --> 00:16:52,129 equipment developed by Hale, whose basic super jet dry bulk design emerged during this period. 159 00:16:52,530 --> 00:16:58,770 The modern pneumatic trailer had found its movement, and once trucking companies proved they 160 00:16:58,770 --> 00:17:03,969 could move cement this way. Another question became obvious what else can we put in one of 161 00:17:03,969 --> 00:17:10,889 these things? The answer turned out to be a lot. Chapter six. 162 00:17:10,930 --> 00:17:17,689 The pneumatic trailer becomes a multi-tool. Cement may have helped popularize the pneumatic trailer, 163 00:17:17,689 --> 00:17:24,329 but the technology wasn't married to cement. Carriers began hauling foundry sand, flour, 164 00:17:24,370 --> 00:17:31,209 lime, mineral products, feed ingredients, chemicals, plastics, and countless other dry bolt 165 00:17:31,209 --> 00:17:38,109 commodities. That expansion created a difficult engineering problem because dry bulk products may 166 00:17:38,109 --> 00:17:44,749 all look like powder or little pieces of stuff to the untrained eye. Scientifically, though, they can 167 00:17:44,749 --> 00:17:51,228 behave completely differently. Particle size matters. Particle shape matters. Density 168 00:17:51,229 --> 00:17:58,149 matters. Moisture matters. How easily the product absorbs air matters how quickly it 169 00:17:58,189 --> 00:18:04,669 releases that air matters. How abrasive it is matters how fragile it 170 00:18:04,670 --> 00:18:11,189 is. Matters. Even static electricity can matter. This is why 171 00:18:11,230 --> 00:18:15,909 experienced pneumatic drivers learn that two products hauled in essentially the same trailer 172 00:18:15,909 --> 00:18:22,269 can unload very differently. Modern engineering guidance emphasizes exactly this 173 00:18:22,270 --> 00:18:27,749 point. Understanding the characteristics of the material is one of the most important steps in 174 00:18:27,749 --> 00:18:34,629 designing a pneumatic conveying system. Consider flour and limestone 175 00:18:35,019 --> 00:18:41,819 fine flower can retain air and become extremely fluidized. A mineral product may be denser or more 176 00:18:41,819 --> 00:18:48,379 abrasive. Plastic pellets are larger particles entirely. Push fragile material to 177 00:18:48,420 --> 00:18:54,499 aggressively and you can damage it. Move abrasive material too fast and you can wear out elbows and 178 00:18:54,500 --> 00:19:00,498 piping. Introduce moisture into certain powders and suddenly a product that should flow freely 179 00:19:00,499 --> 00:19:07,180 can cake or plug. So despite appearances, the pneumatic trailer isn't really transporting one 180 00:19:07,180 --> 00:19:14,019 substance. It's transporting to simultaneously the product and the air. Which 181 00:19:14,020 --> 00:19:20,579 means the driver is managing a two phase flow system. Chapter 182 00:19:20,579 --> 00:19:27,419 seven dilute phase, dense phase and the Science. Inside the hose. There are two 183 00:19:27,420 --> 00:19:33,968 terms you'll hear constantly in pneumatic conveying dilute phase and dense phase. The 184 00:19:33,969 --> 00:19:39,169 simplest way to understand them is to imagine how product is occupying the pipe, compared with how 185 00:19:39,169 --> 00:19:45,329 much air is moving through it. In dilute phase, conveying particles are generally suspended in a 186 00:19:45,329 --> 00:19:51,489 relatively fast moving stream of air. Think of it like dust in a strong, wind 187 00:19:51,849 --> 00:19:58,129 dense phase, conveying moves much more material relative to the amount of gas, generally at lower 188 00:19:58,129 --> 00:20:05,009 velocity. Sometimes as moving beds, dunes, plugs, or slugs, depending on the material 189 00:20:05,010 --> 00:20:11,809 and the system. AIC describes dilute phase conveying as operating above what's called 190 00:20:11,849 --> 00:20:18,688 the siltation velocity. Siltation velocity is an important concept. Imagine 191 00:20:18,689 --> 00:20:24,769 material moving through a horizontal pipe. As long as the air is moving fast enough, particles remain 192 00:20:24,770 --> 00:20:31,689 in trained. Start slowing the air down and eventually gravity wins. Particles begin falling 193 00:20:31,689 --> 00:20:37,868 out of the suspension and accumulating along the bottom of the pipe. That threshold is associated 194 00:20:37,869 --> 00:20:44,228 with siltation, and once enough material settles, the system can become unstable or 195 00:20:44,229 --> 00:20:50,789 plug. So why not simply crank up the airflow as high as possible? Well, because velocity has 196 00:20:50,789 --> 00:20:57,709 consequences. Higher velocity can increase where? Imagine blasting abrasive 197 00:20:57,709 --> 00:21:04,109 mineral particles into a pipe elbow. Thousands upon thousands of times. Those particles don't 198 00:21:04,109 --> 00:21:11,108 politely negotiate the turn. They strike the piping again and again and again. Higher 199 00:21:11,109 --> 00:21:17,589 velocities can also damage fragile products. And producing compressed air requires energy. 200 00:21:17,630 --> 00:21:23,869 So pneumatic conveying isn't about creating the maximum possible airflow. It's about creating the 201 00:21:23,870 --> 00:21:30,819 right airflow for that product and that system. Atlas Copco gives a typical Industrial 202 00:21:30,819 --> 00:21:37,619 dilute phase velocity of approximately 18 to 35m/s. While dense phase systems 203 00:21:37,619 --> 00:21:44,499 may operate closer to 3 to 10m/s, although actual systems vary widely by product 204 00:21:44,500 --> 00:21:50,859 and application. That brings us to another major enemy pressure 205 00:21:50,859 --> 00:21:57,098 drop air moving through a pipe loses pressure because of friction. Add product and the situation 206 00:21:57,099 --> 00:22:03,660 becomes more complicated. Add a bend, more resistance. Add another bend. More 207 00:22:03,660 --> 00:22:10,100 resistance. Run vertically. More energy is required to lift material against gravity. Increase the 208 00:22:10,100 --> 00:22:16,699 conveying distance. More resistance. Change hose diameter. Change particle loading. Change air 209 00:22:16,699 --> 00:22:23,539 velocity. Everything interacts. This is why a driver can unload beautifully at one 210 00:22:23,540 --> 00:22:27,979 customer, and then take the same product to another facility and discover that the system 211 00:22:27,979 --> 00:22:34,400 behaves differently. The receiving system is part of the equation. The length of the customer's pipe 212 00:22:34,400 --> 00:22:41,359 matters. The diameter of that pipe matters. The bends in that pipe matter. The vertical rise in 213 00:22:41,400 --> 00:22:47,799 that pipe matters. The condition of the piping matters. The silo and filtration systems matter. 214 00:22:47,920 --> 00:22:54,919 The trailer is only one part of a much larger pneumatic conveying system. Chapter eight. 215 00:22:55,119 --> 00:23:01,599 Why tank pressure and line pressure are not the same thing. This brings us directly to something 216 00:23:01,599 --> 00:23:08,279 pneumatic drivers watch constantly tank pressure and line pressure. Those 217 00:23:08,280 --> 00:23:13,319 gauges aren't showing redundant information. They're showing what's happening in different 218 00:23:13,319 --> 00:23:19,759 parts of the system. A modern pneumatic trailer operating manual from Biel describes tank 219 00:23:19,759 --> 00:23:26,399 pressure as pressure generated inside the hopper or vessel, while line pressure measures pressure 220 00:23:26,400 --> 00:23:32,949 in the discharge System critically. Tank pressure generally needs to exceed line pressure for 221 00:23:32,949 --> 00:23:38,629 product to discharge effectively. Think of the pressure difference as part of what establishes 222 00:23:38,630 --> 00:23:44,909 the driving force moving product from one environment to another. If the downstream system 223 00:23:44,910 --> 00:23:51,068 becomes increasingly restrictive, line pressure can climb. That may be telling the operator 224 00:23:51,069 --> 00:23:57,829 something product could be building up. Airflow may be inadequate for the solids. Loading a valve 225 00:23:57,829 --> 00:24:04,269 position could be wrong. The receiving system could be presenting excessive resistance. The hose 226 00:24:04,269 --> 00:24:09,709 could be restricted. This is why pneumatic unloading is not a turn it on and walk away 227 00:24:09,709 --> 00:24:16,429 process. The gauges are always telling a story and an experienced driver learns to read 228 00:24:16,430 --> 00:24:23,309 it. Pressure. Sound. Hose movement. Blower behavior. Unloading rate. Valve 229 00:24:23,349 --> 00:24:30,259 position. Product characteristics. The machine is constantly giving feedback long before 230 00:24:30,260 --> 00:24:36,099 computerized sensors became common. The human being standing beside the trailer was the control 231 00:24:36,099 --> 00:24:43,098 system and in many ways, still is. Chapter nine Why 232 00:24:43,139 --> 00:24:49,299 Blowers get hot. There's another piece of physics pneumatic drivers experience firsthand. 233 00:24:49,819 --> 00:24:56,779 Heat compressing air generates heat that isn't a defect. It's thermodynamics. 234 00:24:56,899 --> 00:25:03,899 As a gas is compressed, work is performed on it and its temperature can rise substantially. Then 235 00:25:03,900 --> 00:25:08,659 the air moves through the piping toward the trailer and the discharge system. This matters for 236 00:25:08,660 --> 00:25:15,339 several reasons. Hot components create an obvious burn hazard, but temperature can also interact 237 00:25:15,339 --> 00:25:21,859 with the product and with moisture. Remember that atmospheric air contains water vapor. Changes in 238 00:25:21,859 --> 00:25:27,560 pressure and temperature can influence condensation, And water can be the enemy of dry 239 00:25:27,600 --> 00:25:34,079 bulk unloading. Fine powders that flow wonderfully when dry can become dramatically less cooperative 240 00:25:34,080 --> 00:25:39,439 when moisture is introduced. Food grade applications add another concern. 241 00:25:39,760 --> 00:25:46,560 Contamination. Pneumatic conveying air actually contracts the product. That's important. 242 00:25:46,599 --> 00:25:52,239 The air isn't merely pushing on the outside of a sealed bag, it becomes part of the conveying 243 00:25:52,240 --> 00:25:58,519 environment. Industry literature has long noted that contaminants entering through air systems, 244 00:25:58,520 --> 00:26:05,160 including microscopic debris or in inappropriate equipment lubricant contamination, 245 00:26:05,160 --> 00:26:11,079 can create serious problems when hauling food products, plastics, and other purity sensitive 246 00:26:11,079 --> 00:26:17,799 commodities. That's one reason food grade pneumatic work has its own procedures, filtration 247 00:26:17,800 --> 00:26:24,549 considerations, and cleanliness requirements. The same basic physics may move cement and 248 00:26:24,550 --> 00:26:29,669 flour. The acceptable operating environment absolutely isn't the same. 249 00:26:32,069 --> 00:26:38,829 Chapter ten why pneumatic trailers look the way they do. Now that we understand the 250 00:26:38,829 --> 00:26:45,469 science. Look at the trailer again. The shape suddenly becomes logical. The cylindrical vessel 251 00:26:45,470 --> 00:26:51,468 helps form a pressure capable structure. The cones underneath funnel material toward discharge 252 00:26:51,469 --> 00:26:57,670 points. Aerators or fluids help reduce internal friction and encourage product 253 00:26:57,670 --> 00:27:04,669 movement. The outlets feed a common discharge line. The blower supplies conveying air. 254 00:27:05,389 --> 00:27:12,069 Top air piping can introduce pressure into the vessel. Valves allow the operator to control 255 00:27:12,069 --> 00:27:19,030 where air goes and when product enters the line. Pressure gauges let the operator monitor what's 256 00:27:19,030 --> 00:27:25,819 happening. A pressure relief device protects against overpressure. Hoses connect the mobile 257 00:27:25,819 --> 00:27:32,180 system to the customer's permanent system, and manholes provide access for loading from above. 258 00:27:33,060 --> 00:27:39,299 Modern dry bulk trailers can vary enormously in capacity and configuration depending on the 259 00:27:39,300 --> 00:27:45,979 commodity. Some use a single hopper. Others use several different products. Demand different 260 00:27:45,980 --> 00:27:52,579 volumes because the important highway limitation isn't simply how many cubic feet fit inside, it's 261 00:27:52,579 --> 00:27:59,300 also weight. A lightweight product can fill the trailer before reaching maximum legal payload. 262 00:27:59,619 --> 00:28:06,299 A dense material can hit the weight limit while leaving plenty of unused volume. That is why a 263 00:28:06,300 --> 00:28:12,939 trailer optimized for one commodity may look very different from one design for another. And it is 264 00:28:12,939 --> 00:28:19,779 also why engineering a pneumatic trailer is a balancing act. More vessel structure can increase 265 00:28:19,779 --> 00:28:25,959 strength, but structure weighs something. Every additional pound of trailer is potentially one 266 00:28:25,959 --> 00:28:32,478 less pound of payload. Manufacturers therefore spend enormous effort optimizing vessel 267 00:28:32,479 --> 00:28:39,079 shape, aluminum construction, structural supports, plumbing and suspension arrangements. 268 00:28:39,640 --> 00:28:45,399 A pneumatic trailer must be light enough to earn money strong enough to survive the highway, and 269 00:28:45,400 --> 00:28:51,878 capable of becoming a pressure vessel every time it unloads. That is a remarkable 270 00:28:51,879 --> 00:28:58,879 combination of requirements. Chapter 11 The pressure vessel on wheels. This part 271 00:28:58,920 --> 00:29:04,240 deserves some emphasis. When a conventional pneumatic trailer's pressurized for unloading, the 272 00:29:04,240 --> 00:29:10,919 vessel itself is storing energy. Even seemingly modest pressure becomes significant when applied 273 00:29:10,919 --> 00:29:17,199 across a large surface area. That's why manufacturers establish a maximum allowable 274 00:29:17,199 --> 00:29:24,149 working pressure and why relief devices are critical components. The operating manual for Biel 275 00:29:24,150 --> 00:29:29,829 pneumatic trailers explicitly instructs operators to never exceed the working pressure shown on the 276 00:29:29,829 --> 00:29:34,630 trailer's serial plate, and identifies the pressure relief device as protection against 277 00:29:34,630 --> 00:29:41,509 overpressure, and this is an important place to clear up a common misconception. A pneumatic dry 278 00:29:41,550 --> 00:29:48,229 bulk trailer is not automatically the same thing as the Dot 406, 407, or 279 00:29:48,389 --> 00:29:55,349 412 specification cargo tanks associated with various regulated liquid hazardous materials. 280 00:29:56,150 --> 00:30:02,229 Those Dot specifications have their own construction, inspection and pressure requirements. 281 00:30:02,270 --> 00:30:07,829 For example, federal regulations specify different pressure test requirements for 282 00:30:07,830 --> 00:30:14,670 .406.407 and .412 cargo tanks. Dry bulk pneumatic 283 00:30:14,670 --> 00:30:20,088 equipment has to be considered according to its actual design commodity and applicable 284 00:30:20,089 --> 00:30:25,488 regulations, rather than simply assuming that every tank shaped trailer falls under the same 285 00:30:25,489 --> 00:30:32,369 specification. The takeaway for our story is simpler. A pneumatic trailer isn't merely 286 00:30:32,369 --> 00:30:39,329 a container. During unloading, it becomes part of a pressurized industrial process, which is why 287 00:30:39,370 --> 00:30:46,169 procedures matter. Valves matter. Relief devices matter, pressure ratings matter, and 288 00:30:46,290 --> 00:30:53,129 overall experience matters. Chapter 12 The Machine 289 00:30:53,129 --> 00:30:59,290 Keeps Evolving. By the 1960s, the fundamental concept of the pneumatic trailer was firmly 290 00:30:59,290 --> 00:31:06,129 established, but engineers kept improving it. Aeration systems evolved, trailer materials 291 00:31:06,130 --> 00:31:12,770 and fabrication improved. Vessel shapes were optimized, payload capacity increased, blowers 292 00:31:12,770 --> 00:31:19,359 became more efficient, food grade filtration, improved valves and plumbing became more reliable. 293 00:31:19,400 --> 00:31:26,119 Suspensions changed. Hoses improved, and manufacturers continued attacking the eternal dry. 294 00:31:26,160 --> 00:31:32,999 Bolt questions. How do we unload faster? How do we leave less product behind? How do we reduce 295 00:31:32,999 --> 00:31:39,839 weight? How do we prevent plugging? How do we reduce contamination? How do we reduce wear? 296 00:31:40,039 --> 00:31:46,999 How do we make the trailer easier and safer to operate? And interestingly, some of those 297 00:31:46,999 --> 00:31:53,759 questions remain unsolved in an absolute sense. Pneumatic conveying is still an active 298 00:31:53,759 --> 00:31:59,279 engineering discipline. George Cleansing Historical Review notes that despite more than a 299 00:31:59,280 --> 00:32:05,759 century of development, the physics of pneumatic conveying remains complex enough that aspects of 300 00:32:05,760 --> 00:32:12,559 particle gas behavior are still being researched to this day. Now that's worth thinking about. 301 00:32:12,640 --> 00:32:18,870 Human beings landed on the moon in 1969, we can calculate the trajectory of a spacecraft 302 00:32:18,910 --> 00:32:24,749 traveling millions of miles. But ask an engineer exactly how billions of irregular little 303 00:32:24,750 --> 00:32:29,589 particles are going to interact with one another. The pipe wall gravity, and a turbulent 304 00:32:29,589 --> 00:32:35,429 compressible gas through every inch of a complicated conveying system. And suddenly things 305 00:32:35,429 --> 00:32:41,989 get interesting. Modern computational modeling can help. Instrumentation can help. 306 00:32:42,150 --> 00:32:48,589 Decades of experimental data can help, but the material itself still gets a vote. 307 00:32:49,389 --> 00:32:56,348 Chapter 13. The driver becomes part of the science, and that may be the most overlooked part of 308 00:32:56,349 --> 00:33:03,269 the pneumatic trailer's history. The technology did not eliminate the operator. It changed what 309 00:33:03,270 --> 00:33:09,789 the operator had to understand. A driver hauling drive and freight generally isn't responsible for 310 00:33:09,790 --> 00:33:16,129 physically moving every case from the trailer into the customer's warehouse a pneumatic driver 311 00:33:16,130 --> 00:33:21,930 frequently arrives, carrying not only the product but a major portion of the equipment necessary to 312 00:33:21,969 --> 00:33:27,969 transfer that product into the customer's storage system. The tractor supplies power, the blower 313 00:33:27,969 --> 00:33:33,449 moves air, the trailer manages pressure and product. The hoses become the pipeline, the 314 00:33:33,450 --> 00:33:40,288 customer system completes the circuit, and the driver orchestrates all of it. That's why 315 00:33:40,289 --> 00:33:46,969 experience matters so much in pneumatic trucking. Drivers learn that products have personalities. 316 00:33:47,169 --> 00:33:53,849 Flour does not behave exactly like cement. Cement does not behave exactly like limestone, 317 00:33:53,849 --> 00:34:00,648 and limestone doesn't behave exactly like pellets. One load may want more aeration. 318 00:34:00,689 --> 00:34:06,730 Another may be sensitive to excessive velocity. One customer may have a straightforward short run 319 00:34:06,730 --> 00:34:13,359 into a silo. Another may have a long pipe with multiple bins and a significant vertical rise. 320 00:34:14,199 --> 00:34:20,439 The physics hasn't changed, but the conditions have. A good pneumatic operator learns to 321 00:34:20,479 --> 00:34:26,999 recognize those changes before they become a problem. In that sense, today's driver is doing the 322 00:34:26,999 --> 00:34:32,999 same thing engineers have been doing since the 19th century. Watching, listening, 323 00:34:33,120 --> 00:34:39,959 adjusting, and learning how solids and air behave together. In 324 00:34:39,959 --> 00:34:45,879 conclusion, the modern pneumatic trailer is more than a tank with a hose. So the next time you see 325 00:34:45,879 --> 00:34:50,958 a pneumatic trailer sitting in the yard, consider everything hiding inside that apparently simple 326 00:34:50,959 --> 00:34:57,919 machine. Its family tree reaches back to grain, being sucked from ships in European ports during 327 00:34:57,920 --> 00:35:04,520 the 19th century, its development depended on the arrival of practical blowers and compressors. 328 00:35:04,560 --> 00:35:10,559 Its science grew through experiments investigating how particles behave inside moving 329 00:35:10,560 --> 00:35:17,109 air. Its industrial ancestry runs through pulverized coal, cement plants, and 330 00:35:17,110 --> 00:35:23,710 machines like the Fuller Kenyon pump. Its highway ancestors include dump bodies, 331 00:35:23,710 --> 00:35:30,708 gravity hoppers, auger trailers, and early oil field cement pressure vessels. It's 332 00:35:30,709 --> 00:35:37,029 moment arrived in the 1950s, when postwar construction, interstate highways and changing 333 00:35:37,030 --> 00:35:43,190 cement distribution created enormous demand for bulk transportation. And by the beginning of the 334 00:35:43,190 --> 00:35:49,710 1960s, the pneumatic trailer had demonstrated something revolutionary. The truck didn't have to 335 00:35:49,749 --> 00:35:55,790 simply carry the product. The truck could become part of the manufacturing and distribution 336 00:35:55,790 --> 00:36:02,429 process itself. More than 60 years later, that's still exactly what's happening. Today, 337 00:36:02,789 --> 00:36:09,749 a bulk transit driver pulls underneath a flour silo or loads limestone or cement or lime. 338 00:36:10,050 --> 00:36:15,090 thousands of pounds of dry material enter the trailer. The driver takes that product down the 339 00:36:15,090 --> 00:36:20,609 highway and then arrives at another industrial facility. A hose is connected. A blower begins 340 00:36:20,610 --> 00:36:27,209 turning. Air starts moving. Pressure builds valves. Open air enters the material. 341 00:36:27,250 --> 00:36:33,409 Friction between particles changes. Gravity draws product towards the hopper. Particles enter the 342 00:36:33,409 --> 00:36:39,929 discharge line. The air transfers momentum to them. The mixture then accelerates. It travels through 343 00:36:39,929 --> 00:36:46,649 the hose, through pipe around bends against gravity, up toward a silo, and what looked like a 344 00:36:46,649 --> 00:36:53,490 mountain of solid powder begins to flow. No conveyor belt connecting truck to silo. No 345 00:36:53,490 --> 00:36:59,929 bucket elevator attached to the trailer. No army of workers carrying bags. Just a 346 00:36:59,930 --> 00:37:06,849 driver, a pressure vessel, a blower, some piping, and of course, the almighty physics. 347 00:37:07,330 --> 00:37:12,080 The pneumatic trailer is one of those machines that has become so normal in trucking that it's 348 00:37:12,080 --> 00:37:18,719 easy to overlook how extraordinary it actually is. It's a mobile material handling plant, 349 00:37:18,879 --> 00:37:25,559 a pressure vessel traveling 70mph, a machine capable of turning air into a 350 00:37:25,560 --> 00:37:32,399 conveyor. And every time one unloads, its putting more than a century and a half of experimentation 351 00:37:32,399 --> 00:37:39,039 to work. From 19th century grain ships to pulverized coal to cement plants, to the 352 00:37:39,040 --> 00:37:44,280 interstate highway system, to the pneumatic trailers rolling behind bulk transit tractors 353 00:37:44,280 --> 00:37:51,279 today. And the basic challenge has remained remarkably consistent through all of it. Take 354 00:37:51,280 --> 00:37:57,759 something heavy, take something solid, and convince it to ride the wind. This 355 00:37:57,760 --> 00:38:02,919 concludes our special presentation of Trucking Up History, The Science and History of the Pneumatic 356 00:38:02,959 --> 00:38:08,739 Trailer, brought to you by Bulk Transit. Thank you so much for listening to this episode of Always 357 00:38:08,739 --> 00:38:14,100 Pneumatic, Never Static. We look forward to bringing you more documentary style episodes 358 00:38:14,100 --> 00:38:19,699 sometime down the road. Don't forget to submit your quiz for your entry into our next drawing, 359 00:38:19,700 --> 00:38:26,179 because there's a lot of great information to get quizzed on in this episode. I'm your host, Marcus. 360 00:38:26,220 --> 00:38:30,100 Thanks again for being here and clicking download today, and don't forget to head over to our 361 00:38:30,100 --> 00:38:36,979 website podcast.bulktransit.com for all of our episodes, all of the quizzes, and much, 362 00:38:36,980 --> 00:38:42,859 much more. We'll see you next week at 5 a.m. local time for another episode of Always Pneumatic, 363 00:38:42,860 --> 00:38:49,820 Never static. Until then, be safe out there, drivers. And that's all she blows for today's episode 364 00:38:49,820 --> 00:38:56,100 of Always Pneumatic, Never Static. Your number one and probably only Pneumatic Trucking podcast, 365 00:38:56,100 --> 00:39:01,738 brought to you by Bulk Transit. Thanks for rolling with us today. Till next time, stay safe. Keep those 366 00:39:01,739 --> 00:39:03,938 lines clear and keep it pumping.