Cement, fly ash and those types, unloading. Top air?

Never used top air with cement products. Lime and sand are a different story. Cement powder has enough fluff to let the aerators do the work.

 

Hope this thread isn't too dead to ask you all something. Started doing pneumatics about 3 months ago. 99% of the time I'm unloading Cement into a silo at 2 different places. Place #1 always takes about 1hr and 15min to 1hr 30 minutes to unload. Place #2 always takes about 45min. They both seem to have the same distance of piping before it gets to the silo. Always run tank at about 14-15 PSI at both places but get different results. Do I need to do something different at place #1 to unload it faster or is this pretty much "you get what you get"?

Edit: on a side note, ever heard of anyone unloading the middle hopper first (on a 3 hopper trailer) then the other two?

 

Depends on the number of bends/turns in the pipe. they use those big sweeping bends to limit friction loss. with liquids a 90 degree elbow cuts the flow rate in half.

One silo must have a different amount of piping or a vent restriction unless the product density is different like you will see in plastics..

Look at the shape of a three hopper dry bulk trailer. with cement, blower heat is not a problem and starting in the middle will unload most of the product...your mileage may vary...it has been done before.

 

It might be the baghouse is dirty on silo #1. In that case, not much you can do aside from telling the plant operator. Do you have a lot of back pressure when unloading in that silo? (In case you don't know what I speak of, next time unloading there, close all product valves and just blow air into the silo. Watch the line pressure gauge. Anything over 3-4lbs is gonna slow you down.)

That's really all that comes to mind.

For the last question, about unloading the middle hopper first, I do it alot. Always with flyash. Just a preference. I doubt it will affect unload times. As was said earlier in this thread, ask a question about unloading to 10 people and you'll get 12 answers. All may be correct, too.

 

Only time I ever put air in through the top was when I was needing to pack down a light fluffy product (i.e. hydrate lime) to get more in the trailer. While unloading, any air I needed to put into the trailer, I'd run through the aerators. Air passing through the product is what makes it flow, which is the purpose of the aerators. Putting air in the top packs the product, and that just isn't helpful.

 

If the baghouse is plugged up, there's nothing you can do. If the dust collector isn't running, ask the plant operator to turn it on. Sometimes there's enough buildup on the inside of the silo pipe to cause a restriction. Before you connect your discharge hose, take a mini-sledge and give the pipe a few good whacks right above the camlock fitting.

 

45 minutes a hour and 15 isnt too outrageous. Different silos breathe differently.

You forward pot first then middle and later the aft pot. If you tried the middle pot, and she gets to shaking and singing... you will never see that pot get empty, you follow me? (A little bit of "Duh" in there he he)

The best benefit to front middle and rear last to be empties is that once your front pot is empty and nothing but tank air, it's a option to "Punch" your line once your exhaust turbo starts choking or your discharge hose stops snaking.

 

I open my top air when starting out building pressure, but that's only for one reason, and that's to clean out the top air pipe. The pressure relief and tank vent is on the top air pipe on my trailer, so if you have any product in there and have to open the vent at all, or the pressure relief goes off you will be thankful you did that! The one product we haul is "fluffy" so the trailer is full when getting loaded, and takes a little while driving to get it to pack down, and I have forgotten to close the blowdown vent after getting loaded, and have had to hit the brakes hard only a couple miles down the street, and have had the product move and come out the blowdown, and leaves product on the road, so you can imagine that the top air pipe could be completely full of product just from normal driving.

I have tried using just top air on flyash, to try it since it's pretty much a free flowing substance, the stuff we get around here anyways and it didn't make a difference in time for me atleast.

It depends on where I go as to how I unload, whether it's front, middle, or back first. We keep the same trailer all the time, so if go someplace that it might not all be able to fit, bc we take product back to where loaded and unload the rest, unless getting same product again will topload on top of whats left. I will unload the back, middle, and then front. Especially this time of year don't want most of the weight on trailer axles and not have any on the drives, could make for an interesting ride! The issue is if you have setback dolly legs where they are behind the first pocket, you can not drop the trailer as the weight will be forward of them and will teeter on them, depending on how much is left and you will find out you have a really bad day! But most of the time I unload middle back and then front. The other time I change it up is if I think I have a set of vibrators starting to plug up, I will unload that pocket second after letting another get completely empty as the vibrators for the empty one will assist in getting the product moving somewhat in the pocket that the vibrators may be plugged up and then let that one go completely empty and then start last one, and hoping that it will clean out the plugged up vibrators. Doesn't work if you did get unlucky and get product pushed up to almost the air pipe.

As for the slow down in time, as others have stated could be any number of issues, backpressure, buildup in pipe choking it down, etc. the only things I could recommend is to play around with it, you may find a sweet spot that allows it to unload a little quicker. May drop your pressure a little, sometimes a couple pounds could make a huge difference, some of our guys think you need to run it at 16-18 psi all the time and hope to get done quicker than anyone else, and it actually slows them down bc now the product is not flowing but you are trying to force more through the pipe. Some places we go to you can unload a lot faster running at an idle vs bumping it up and then there are places like you say, "You get what you get" where it doesn't matter what you do it takes the same amount of time. It's just one of those things you learn as you go, some places you know it'll take you an hr and half to unload, it's those places where it may take you 45 mins to unload all the time, and then takes an hr and 15 or longer to unload that you know there is an issue someplace that just popped up.

 

Exhaust turbo?