Chapter One. Concrete Pump is all plugged up.

Concrete Pump is all plugged up.

The title of this paper should be self explanatory. This is going to explain the most common problem in all types of concrete pumping, how it happens and what to do about it. In this installment we are going to look at what that term means. We’re going to dissect the “plug” and learn about it in the hopes that knowledge truly is power. The goal is to give every operator, new or veteran the power to safely solve the oldest and most common problem in the industry. As this article progresses we’ll see what to do when it happens in different situations and a variety of equipment. More importantly, what not to do and why.

The number of possibilities are endless. The purpose of this is to teach operators the skills necessary to deal with a plugging problem as it happens by providing some facts and proven technique. Most of what a pump operator does everyday comes down to making good decisions in the field while under pressure.

If the operator is armed with good information and trained well, his decision making process becomes automatic since he has been taught to handle the situation. Panic and idiotic mistakes cause injury or death. When the operator has been trained well he reacts instinctively and does not hesitate . His training provides him with a plan before the incident even unfolds. That instinct will take over and the operator solves the problem confidently with a minimal amount of down time, if any. Only those that are unprepared have to stop and think about what to do next, only those that have a plan are truly prepared…

We take the equipment for granted too often because normally when everything is going well our level of confidence is high. We find ourselves “in the groove“ and we do our jobs and make it look easy to observers. With experience comes confidence. What we’re going to explore in the following chapters is what has not been taught to many of you because it just hasn’t happened yet. You cannot learn from what is not there or what nobody has described. The single biggest secret to successfully overcoming these hurdles is understanding how and why they occurred. Once that is known, the appropriate action can be initiated. That is why we’ll start with what a “plug” is, then the how & why. What to do will come later and will make much more sense to everyone after they have absorbed the information contained in these first pages.

What separates the best ops from the average is how the sudden, unexpected interruption of their ‘rhythm’ is handled. These interruptions can often take place in milliseconds and how quickly and appropriately the operator reacts can mean the difference between a successful outcome with a signed invoice, or a failed pour. When working with machines as powerful and complex as concrete pumps, whether it be a small line trailer pump or a long boom, the goal is always the same…Do the job, do it safely, do it like the customer wants, make everybody happy and get paid for the work. The goal is easy to understand…it’s the process that gets confusing because of the never ending variables in the normal everyday job of running a pump. Virtually every minute something changes without warning. Being a good, qualified pump operator means having the confidence and the skills to cope with these variables as they appear. Knowing what to do. Being able to assemble the available information and combine that with training and use that to resolve the problem. Plugs can happen that fast as we know.

The operator has to be faster.

To begin, lets define the problem. What does the term “plugged” mean to the concrete pump and its operator?

Basically its an obstruction or blockage in the pumps delivery system or sometimes in the pump itself. This is how it gets ugly real fast. We know what kind of pressure these machines are capable of generating. Suddenly having nowhere to go increases the risk of something coming apart (exploding) when it comes to plugging. The weakest part of the system is at risk where ever that may be.

Whatever pressure that was required to move the material up to the place that it plugged, will instantly increase as the plug sets itself. This pressure will seek the easiest and fastest way to relieve itself. This should happen immediately by the operator reacting and hitting the ‘stop’ or ‘off’ button before something blows apart. Then reversing the machine to remove the head pressure so its safe to stop and evaluate what is happening. What we don’t want to do is to hesitate and allow the machine to continue to build pressure and find its own way of relieving the pressure by blowing something apart. Not even brand new pipe can always be trusted to stay together with the power of today’s concrete pumps.

A good operator was already on the button as he heard the machine bog down, or felt the spike in pressure as the pumps noises change signaling to him that something is not right. No one else would notice this but a good operator would. When pressures (resistance) suddenly increase (signaling that there is a plug happening) the load on the pump engine increases and you will hear it. This is the first clue of what is taking place.

Another way the built up pressure can be relieved is by a piece of your machine coming apart as the pressure extremes cause the weakest piece in the hydraulics to come apart.

Whether its delivery line or hydraulic line the result is similar to what a grenade does…pieces of debris (rocks, oil etc) flying in all directions causing damage or injury to anyone and everything within range. Not knowing exactly which piece will “let go” only compounds the problem making it all the more dangerous.

I have seen an elbow blow and take out the windows on a dozen cars parked nearby. I’ve also seen aggregate go thru the fender of a car. If aggregates that are flying thru the air as if they had been fired from a shotgun will go thru the fender of a Chevy P/U…they’ll go thru you as well.

Plugging can be very dangerous.

Just because you haven’t seen something break as of yet, doesn’t mean that it won’t happen sooner or later.

A big problem is that plugs also cause the hydraulic pump to automatically increase the power that its applying so the situation gets worse as its taking place. Pressure builds as the material stops flowing as the plug becomes ‘set’. This can snowball and get out of control so fast that the original plug can become secondary to the blown turret pipe or the blown pipe on the mast of a placing boom or the reducing elbow on a hi-rise trailer rear end. When you’ve blown something apart, the problems then arrive by the truckload….no pun intended. The operator suddenly has multiple issues to sort out and has to effectively deal with them all. This is why we train and attempt to explain these things to the new operator when he has not seen then yet.

Often, a rookie might go solo without having had the benefit of getting big time plugged with a veteran there to show him what to do and how to safely get it pumping again. The rookie operator that has no experience with plugs, stands a very good chance of loosing control of the pour and loosing the boom or the line. Once plugged, it’s easy to blow something apart, now there’s system to repair or replace. Trucks keep rolling on site, getting hot and there’s the inspector reminding you that you can’t have any more water since the temps have gone past 90* and the mud’s past 90 min. and he’s being an ass talking about rejecting some loads right now and you’re not even close to having this mess sorted out yet.

While all this is going on and overwhelming the new operator, there is also the partially completed SOG, or wall or column that’s only half full, and the old mud that’s been sitting in the pump not moving for the past 20 minutes as the drama unfolds.. It’s starting to look like a long day ! It could be..

Only if the operator allows this to get away from him. If he was fortunate enough to be trained in plugging and has been taught what to do and when to do it by a veteran operator that was kind enough to explain things in detail, then the rookie will finish this pour and go home in one piece. He’ll react to the challenges as if it were second nature and not waste a minute having to think about it.. Besides dealing with any damage, there is still the small problem of the plug, the several loads of material, the customer, the pour…all under control if he paid attention to his training. Just another day at the office.

Describing what a plug is will now get a little more complicated as there are many reasons why and how. Since there are almost as many different types of “plugs” as there are leaves on a tree I’ll outline the basics and we’ll explore those in detail as we go.

So, what is a ‘plug’ ?

As previously stated, a ‘plug’ is an obstruction or blockage in the delivery system or in the pump. The typical plug up is usually some form of the material that was being pumped. it’s lost its ability to lubricate itself or has changed in some way to render that piece of material un-pumpable or impassable. Each plug has its own characteristics and its own requirements to clear, so this first installment will examine the basic concrete plug or material plug. First, lets look at the many basic forms of plugging up…we’ll eventually visit each of these and learn how to prevent, and what to do should it happen to you.

This list has the more common types of plug-ups. Material plug (various reason, see below) Plug on Prime (in ground pipe, boom, deck or turret) Material Cylinder packing/plugging Plugging in concrete valve (rocked up in Tube, etc) Rear end plugged (sweep or reducing Elbow Separation plug

Dry plugging

Bleeding mix

Gap graded course sands

Lean mix

Flashing

Plugged in reducers (rear end, on boom, on tip, on ground)

Foreign object in system (where’s my hammer?)

Twin Pipe (a good one)

Pumping downhill or straight down.

Plugging while reversing/sucking a ball

Water wash plug

Dirty system plug

Clinkers

The list goes on….

Basically, it don’t take much to plug up a concrete pump. There are thousands of ways to do it, fewer ways to resolve the problem and continue pumping. Once you understand the problem, you can apply what you know to the current situation and find a solution. First is to locate the plug, next would be to remove it, and study the overall situation to try and learn what caused it. This goes a long way toward preventing the next one that could end in disaster. Utilizing the knowledge that’s been acquired in past experiences or in articles like this can is how an operator gains useful experience in dealing with the unexpected.

Answers that the operator has seen put to work and used successfully that he will use down the road someday for reference. Every challenge that’s been resolved becomes a tool the operator can use again at some point in the future where there had been no specific instruction, just examples of how to evaluate and react.

Non-Specific Material Plug

The very thing that you’re pumping and have been pumping suddenly ‘turns’ on you and will not move. I can tell you that every single material plug has something in common. The loss of lubrication. To further explain what that means, we have to go back a couple steps in training and review what we know. Concrete can be pumped because of the “self lubricating” principle. This simply means that the cement is the lubricant. Like oil, it can be thick or thin but always slippery. Whenever a concrete mix is made the most basic ingredients will include cement and water and together these make for a very slimy material that’s both product and pumping lubricant. As the mix gets its other ingredients added, the level or amount of lubrication gets reduced or at least altered. The mix must retain some of the slippery properties in order to be pumped. It must be capable of flowing or remaining plastic, it must be able to support itself without separation, and it must contain enough cement to supply lubrication in the pump and system yet meet the demands of the mix design.

When a typical mix that has been pumping well suddenly plugs… there is a reason. Look at the basics of the mix. What changed? How does the material appear compared to how it looked in previous loads that day? How is the consistency? In a 100 cu. yd pour that’s somewhere between 8 & 12 loads. Each truck might get the same batch, but you have to keep in mind that there might have been something in the drum before it was loaded…washout from the previous load, rocks of a different size/grade, old slurry water, even a pile of clinkers from the driver beating the buildup off his fins and charge hopper. That’s why we try to run our pumps with one eye on the pour and the other on the hopper so we can see whats coming down the chute. If you’re really watching and focused you will see the plug before it gets pulled up in a cylinder and you can deal with it there, instead of risking boom pipe, ground line, or the damage caused by some thing coming apart. If you see the problem, now is the best time to deal with it.

Common material plugs are almost always the result of something that’s contaminated the material that you’ve been pumping. What else has changed? Its so easy for clinkers to hide in the mix as it flows thru the hopper that they can make it all the way thru a boom and get hung in the tip elbow when they just happen to get turned the correct way to act like a butterfly valve and block the flow,.

The other big cause of a plug in an otherwise good mix is water. Drivers will often add a shot of water at the last revolution to chase the trailings down the chute so that you get it all and there is less to scrape out of the chute. If this splash is not well mixed with the next load it will be sucked in the pump as a single cylinder full of water that will cause the mix to separate at some point…in a boom it’ll be an elbow or deck if you just happen to stop while that wet splash is passing thru the deck…that can be real bad and might be very difficult to work out if you do not catch the pump and reverse the instant the pressure surges…packing it in the deck and into the turret offers nothing but heartache, so pay attention and avoid the water splash and shut downs IF you have one in the boom. A ground pump will be effected in a reducer somewhere. Never ever pound a reducer. That’s hopeless but I see people trying…If there is a plug in the 5” end of the reducer, why or how exactly is it supposed to make it thru the 4” end?

Just take it off and shake it out

The water splash might be something that you have to do for various reasons but it will cause good material to plug. If it absolutely has to be done, have the hopper full of concrete so the water will stay on top since rocks and sands/ mix are heavier and will be pulled in the pump first. That way the mud picks up just a little of the water over the next few yds that come down the chute as the falling mud passes thru the water that’s floating on top. This will spread the water out over several yds and lessen the chances of plugging. Sometimes the mix can be so marginal that the few rocks that were already in the truck when it was loaded can make the difference. This is harder to see but if its enough to cause a plug you’ll be the first to know… It could be anywhere, but always consider the rear end reducers first. A few good reverse strokes watching to see how much and when the mud starts to rise in the hopper will tell you if you got a ‘bite’ on the plug and were able to reverse it back into the hopper where the valve can chop it up and remix it into the rest of the material in the hopper.

In the event of any material plug, that’s how it should be handled. If it’s a ground line you have to find where the plug is and most likely open the system. A stand pipe can be reversed but that’s not an everyday line pump job. Should this happen in a boom, reverse the pump, watch the level in the hopper and attempt to go forward gently until you get material flowing from the discharge again. If it tries to plug again, you must determine if its in the same place. This might mean there is another problem and not just a simple material or mix plug. Do this by reversing and keep reversing until there is mud definitely coming back into the hopper. If you hear and feel the pump “thumping” real hard as the valve cycles and the mud sucks down fast then rises with each cycle but nothing really comes up in the hopper, you’re not getting the plug to move.

You’re pulling a big vacuum on the system because the plug is in there so tight. Go forward gently and this time count the strokes to see how far the plug is from the pump rear end. This is a term that every operator should be familiar with and know how to use. Counting strokes tells you where the mud is in the boom or the vertical so you don’t have to guess. If you do not know, learn how many strokes it takes to get to the highest point on the boom, or the tip. Remember, each machine will be different so don’t count the 39m 25 Schwing and then try to use that info on a 21c Putz with a 55m boom.

If your pump refuses to pull the plug back, now its urgent that you ID where that plug is and get the tools and deal with it. The pump is your best friend, so use its power and use gravity to assist you. Once you break open a pipe, the pump can no longer help you suck out a plug. I have seen water or slurry poured in the tip and the boom stood up then reversed to help loosen a plug and suck it back, and I’ve seen the blow out cap installed and charged to push while the pump sucked. Point to remember…99% of all plugs are simple lack of lubrication. Replacing that somehow,. If practical can save your pour and your pride. Once the plug has been located and removed by opening the system or however it was done, you’ll see that the jammed up wad of rocks and sand is so packed in there that it took a sledge hammer to beat it loose. When you find and remove the plug, LOOK at it and see what it was made of. Knowing that will help you avoid doing it again. You can see if it was washed clean like too much water went thru it or if its just a wad of nothing but rocks. Whatever it is, that’s from a chunk of bad material that was sent thru the system, but its jammed in there so tight because the operator failed to get in the switch fast enough…Material plugs are the easiest and usually a one time event. They are the result of something changing in what was a working mix and getting out of spec somehow. If they become chronic and you expect to deal with a plug every load, all day long, there is something else going on and it needs to be addressed. Simple material plugs aren’t constant. Poor mixes, contaminated mix, poor water control or aggregates are what cause chronic plugging and that is what we’ll look at in following chapters.

NEXT CHAPTER: PLUGGING ON the PRIME