Pneumatic trailer unloading

Discussion in 'Tanker, Bulk and Dump Trucking Forum' started by Lazy, Jun 29, 2021.

  1. Lazy

    Lazy Light Load Member

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    Ive been training on pneumatic trailers with the new job. But taking my time off now so i thought id ask some questions. I should start off with what i know, or what i was taught. Hauling Frac sand. The idea of these trailers is to maintain proper air pressure and control the flow of the product to which the driver seems fit?


    Step 1 obviously would be to hook up the hose to the blower. Before you turn the blower on make sure all valves are closed except the top air line to charge the tank with air pressure (not above 15?).

    Step 2 when the tank has enough air pressure open the pressure control valve and close the top air line. Now its time to open just one product line and unload one at a time.

    Thats pretty much all i understand for now. Questions i would like to have answered. What does it mean if the air pressure gets too low (besides an air leak somewhere)? What does it mean if it gets too high? When or why should i be using the blow down valve? When and why should i use the aerator valve?

    PLEASE add on to this and answer those questions. Maybe my process is wrong and i dont understand or could use improvement.
     
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  3. Northern Nomad

    Northern Nomad Light Load Member

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    Hi,
    Your tank pressure and line pressure will vary depending on the product you are hauling. However, you don’t want to exceed 15 PSIG.

    Step 1 is correct. Hook your hose to the blower, make sure the valve to charge the tank is open all the way, blowdown valve is closed, engage PTO, and set RPM’s.

    Step 2 is mostly correct. When you have enough tank pressure, leave the tank valve open, then open your line valve to the desired position, and then open up a product valve, usually all the way. And, do one pocket at a time. Sometimes you can open the next one without having to recharge the tank pressure, sometimes you can’t, depending on the product.

    If the pressure gets too low, usually that’s an indication that the pocket you are currently offloading is beginning to empty, or you have a leak.

    If it gets too high (above 15 PSIG) that’s usually a sign that your line is plugged. Be sure to learn how to unplug it!

    You use your blowdown valve when you are all done and ready to disconnect. This discharges all the remaining pressure in the tank. This stays open after your done and until it is reloaded. Also, you will use this in case of a plugged line.

    You will use your aerator valve when you are offloading. This too depends on the product you’re hauling. Sometimes I use it, sometimes I don’t, depends.

    These should help you. I haul talcum powder, plastic pellets, resins, soda ash, and other products in a dry bulk tank. Some people may have a different process, but this should give you a better understanding, hopefully. You’ll like it once you get used to it, I enjoy it more than any other type of trucking. Good luck
     
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  4. wis bang

    wis bang Road Train Member

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    Charging the tank with the top air -or- the aerators depends on the product. Cement needs to be 'fluffed up' with aeration while plastic pellets will flow on just tank pressure.

    Once you open the pressure control [line] and open the product valve slowly.

    Then using top air and the line air you could raise or lower the tank pressure as needed. Same idea with aeration an line pressure.

    DITTO on learning how to unplug the line. happens to everyone.
     
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  5. Suspect Zero

    Suspect Zero Road Train Member

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    I have never done sand so I can't really comment on anything related to that type of unload.

    The way you have listed is a decent jumping off point to start in general terms. As you do it more and become more familiar/comfortable with it you will start to experiment and make adjustments and develop a system that works for you.

    I would say that just after you start the blower open the bottom air valve (pressure control valve, proportioning valve) and close the top air valve for a moment to make sure that the pipe under the trailer and all the lines/hoses to whatever you are unloading into are clear, then reverse the valves again to pressurize the trailer. If you have a blockage you don't want to wait until the trailer is pressurized to find out. This may not be an issue with frac sand, I have no experience with it, it's just the process I follow when starting up for any product.

    If you are still training I would say take lots of notes. It may seem dumb, and some guys looked at me like i was silly when I did but once I got out on my own I was glad to have them. You never remember all the crap you think you will.

    Using aerators will depend on what you are unloading, some stuff needs them, some doesn't.

    Be nice to your hoses. Dropping them on the ground will eventually leave them out of round and have a lot of people pissed off.

    Just a couple very small thoughts. Sorry I can't comment more, but I have no experience with what you are going to be unloading and don't want to tell you to do something that works for what I do but won't work for what you are going to do.
     
    Last edited: Jun 29, 2021
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  6. wis bang

    wis bang Road Train Member

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    2 good points.

    The first one should be a standard thing as the product valves may/will leak into the discharge line and starting to unload with a slug there will cause problems.

    We ran caustic soda beads where the blower intake air went thru a huge desiccant canister to insure no moisture and step one was to blow the discharge line thru to the customer tank for 15 min. to insure the pipes were 100% dry. Drop a few on the ground and watch them melt from the humidity in the outside air

    Aluminum female hose ends get egg shaped from dropping.

    Learn about all types of hoses, jointed flex stainless hoses can be one-way or two way, important to know and they shouldn't be laying on the ground when you vacuum load.

    Pharma grade resin [$1.00 a pound] gets downgraded over a few specs of black stuff sucked in thru the hose to a common grade [$0.20 a pound] for one whale of insurance claim.
     
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  7. Lazy

    Lazy Light Load Member

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    I'll come back to this post often thanks for the replies. The guy training me would sometimes use the blowdown valve during unload. I assume this was to relieve some pressure? For whatever reason. And i did plug up the hose twice, he showed me how to reverse the blow to unclog it. He never used the aerator for the sand so i was unsure. Just have to learn what works best for me
     
  8. Long FLD

    Long FLD Road Train Member

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    Lots of good tips for you here. I would always have air going through the product line before I’d close valves to build tank pressure. It was just a habit I had, send air out the product line and make sure you don’t build line pressure to verify their pipe is cleaned out.
     
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  9. RockinChair

    RockinChair Road Train Member

    The blowdown valve should remain closed during unloading. If tank pressure gets too high, open the discharge valve a little more so that less air gets diverted into the tank and more gets sent through the discharge line.

    You don't need to close the tank valve when opening a product valve because tank pressure will drop a little bit even with the tank valve all the way open, and then if it doesn't recover you can pinch back on the discharge valve to increase the tank pressure.

    Regarding tank pressure, aerators are used to fluidize the product being unloaded. So unless you have a product that flows freely, use them. Top air is good for "fluffy" product that needs to be pushed down, like hydrated lime.

    When starting your blower, keep the blowdown and discharge valves all the way open and the tank (whether aerators or top air) closed. Once you got your blower at the proper RPM close the blowdown, so that all the air is sent through the discharge line. Once you're sure the discharge line is clear, open the tank valve then close the discharge valve to pressure up your tank.

    Once you get your flow stabilized, if you're not having to keep your discharge valve all the way open, you can try opening a second product valve to cut down on your unloading time.
     
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  10. Lazy

    Lazy Light Load Member

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    Anything to do when turning the blower off?
     
  11. wis bang

    wis bang Road Train Member

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    After going back thru all of the hoppers and blowing the line some, open the blow down and then throttle down but let the blower keep turning to cool down.

    Pop the air hose off the blower outlet to kelp it cool faster.
     
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