Chapter two of Concrete Pump all Plugged up.
Todd 07-22-2011
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Here is the link to All Plugged up incase you want to read Chapter one

But for those of you who want to read it here itis. I would like to thank Lee Horton for his hard work.


 Plug on Prime


Without a doubt, the most common of all types of pump plugging. It has the potential to happen everyday, to any pump and every operator. The plug on prime is also the most common of all “operator error” pump problems. Why? Because plugging on prime is the direct result of loss of lubrication in a situation that almost 100% under the control of the operator. Occasionally the pump might malfunction during the critical 3-4 seconds that it takes to move material from the delivery cylinder to the tip hose or beyond. Even if that happens, its easily worked out if the operator has been taking care of business and the machine is able to be cycled manually.


The loss of material lube can come from a variety of sources. It can be from separation in a water prime if not done properly, from concrete that has been overdosed with “Super-P” and placed behind a thin primer, slick that has been watered down too much or not been allowed to gel, and whats the most criminal of all prime plugs, dirty boom pipe or ground system. I've been saying it for decades, what you did yesterday afternoon has more to do with today than right now...That's why I am an advocate of water washing and it can be done with any type of aggregates and sand as long as the material was able to be pumped, it can be water washed. The trick is in the technique. Poor technique and you may as well plan on a plugged boom. Question is, do you want it today or tomorrow morning? Pay me now or pay me later...doesn't matter.


Lets start with ground system and stand pipes & trailer pumps in general,. There will be lots of this stuff that does not apply to many grout pumpers, Olins, Maycos, Chem-grout and other slurry pumping applications so please keep in mind that most of this is about concrete mixes that contain aggregates. Although its very easy to plug up a slurry pump by priming with dirty system or simple laziness, its easier to screw up when there are rocks involved. I've also seen some well meaning dispatchers order some 5sk slurry prime to pump some 9sk grout....



that's where this battle begins. The key to many pumping issues as well as prime issues is and always will be loss of lubrication. I'm certain that many guys will get tired of hearing that term but it does explain most of the pump-ability problems and prime problems that we encounter. Learning what that means and applying it to the situation that you encounter will assist you in finding a quick resolution.


Priming is not actually what the word describes...pumps do not need to be primed. Pistons pumps need an energy source and that is about it. If that's available the pump is going to move and push or exert force on whatever is in front of the pump pistons. Lubrication enters at this point. If concrete lubricates itself, then it leaves something behind as it travels, Right? So, as the pistons push material thru the cylinder into the transition and into the system where the concrete must transform from sometimes a 8” or bigger material cylinder thru a reducing valve then into a transition piece and finally another reduction until it hits the delivery system size, this all requires extreme lubrication and ever increasing force to make all this happen. Again, as the material travels it leaves some lubrication behind, so the first “slug” of concrete is quickly becoming leaner and leaner until it can no longer lubricate itself. This doesn't take long can happen within 3 ft of the hopper. Because of the need to change shape, accelerate, respond to pressure, reduce and swirl thru bends, the requirements for self-lubrication are very high at this point. Its also a very good place to find out if the material is going to be a problem before it gets 150' down the road where its much tougher to deal with a plug.


The term “priming” means to lubricate the system. It is the use of some form of compatible liquid to lubricate the pipe/hose walls so when the concrete enters there is nothing lost as the concrete travels thru the length of the system. The longer the system the more prime needed. The longer the system the richer the prime need be because it will leave a little behind as it travels and it is absolutely possible to plug on 9sk slurry if the distance is far enough or the grout starts out dry enough. My personal method of choice is to send some water ahead of grout so that the slurry can remain wet and useful longer and travel further. If its extreme line pumping 1000' or more, I'll apply CYA to the process and send water first, then gel followed by the richest grout available. If you want a long day...plug up 800' of 5” horizontal while priming.


Water Priming....

Many areas use plain water to shoot a 100 ft of 2 or 3” line on pea gravel or other small line jobs. There is some method to the madness. If the hose or line is a minimum of 3.5 times larger diameter than the largest aggregate, the concrete can be pumped easily and small line work is always richer by ratio than most large aggregate work so a good dose of water ahead of the concrete wets the system enough to let the richer than usual mix pass thru without much trouble. If the distance is greater, then gel can be used. The old days of 2&2 are about gone..2 bags sand and 2 bags cement on the first load. I'd bet that most people today haven't ever heard that term before...


Time consuming and the consistency of the slurry was poor at best, often made useless by too much water since there was rarely a good method of mixing beyond a stick and a bucket. Although having some cement in the water prime is better than none at all, it can be counter productive because the operator assumes that he can use more water since he has some cement in there...not true. If using a cement slurry it needs to be pasty and thick enough to coat the pipe much like paint has to cover a wall. Thin it too much and it doesn't cover well enough to do any good.


The “sin” in water prime on a pea rock pump (or any other) is usually in dirty system. Hoses that did not get washed, or get rolled out completely. It only takes a handful of non-lubricated material to plug a small line. Because pea rock is richer, its harder to plug up from the water causing a separation plug. Its almost always dirty system. The bad news in pea rock is that you only get one option should you blow the prime...since many small line pumps with ball valves or a stator do not have a reverse, its in the operators best interest to roll out his hoses each evening when loading to make sure they are clean. As the pump plugs, the operator must pay attention and be quick on the switch or he can easily blow a hose to pieces and/or jam a plug in a hose so hard that it has to be beat out and that is what will damage that hose and cause it to blow next week.....If your 2” was supposed to be hit with a 10 lb sledge hammer it would have a target painted on it.


An operators full attention is required when priming. If he hesitates as a plug appears he can make things lots worse by not being on the switch fast enough.

What not to do when the water prime doesn't work?

Never ever wind it up and hammer it. ALL that does is cause the system pressure to build up, then some poor soul has to go to the appropriate clamp with a shovel and try to flip the clamp open without being killed by the flying debris as the line flies apart under high pressure. There is no other way to relieve the pressure on many pea rock pumps other than popping open a clamp. THAT is why you decide on your prime wisely and exercise good judgment. If the mix and distance will tolerate a water prime, fine, its your call. Since gel is usually always available its a simple matter of risk assessment.


If the line does plug and does get opened without injury to anyone, the plug has to be found, completely removed, preferably washed out, then the system has to have some lube placed back in for the rest of the distance. Whatever is appropriate. Whatever is available. Time sensitive, use what you have instead of screwing around as the rest of the system sets up and the mud gets hotter. This is where your good judgment comes in.


 Big line trailers are similar except that they DO have a reverse, but the improper use of reverse on a trailer can create as much havoc as not having it. How? Concrete is very heavy. One cubic foot can easily be 250lbs depending on the density of the rock and the quantities of rock. When a system is laying down, the mud's too heavy to be pulled by a reverse. It can be pushed if adequate power is available but reversing is pulling it apart and that creates a separation plug of sorts. The materials lightest parts will try to reverse but the heavier rock won;t, so you end up with separation plugging in the flat line.


A nice stand pipe will let you do what you want since gravity is just as good as HP when you need to go the opposite direction. Hit a plug going up? Reverse it hard and WATCH what comes back in the only takes 2-3 rev strokes to see if you are pulling material back or if the plug is still in place and not allowing the mud to flow backward. If that happens the reversing will be accompanied by a distinct thumping noise and the characteristic hopper level shooting down with each valve cycle if its pulling a vacuum. This takes a little finesse to work out...gently move forward to get a “bite” on the plug, count the strokes backward...continue to do this until you can accurately tell if the plug is moving or not. If it moves it can be worked out. If it does not move, then counting strokes in reverse will help you in discovering exactly where it is that you need to intervene manually...

Plugging on prime in a stand pipe is rare mostly because there is always good grout available, and the system is always cleaned by blowing with water and 2 balls...right? You did find both balls yesterday, didn't you? Clean system primes easy. Its a fact.


Downhill prime plugs...

 Not the everyday pour but very easy to get screwed up on the prime. Always requires good grout since there is more at risk if there is a plug. Often the first thing to enter the system will be a “pig” or a simple wadded up newspaper that's been soaked in water. This prevents the grout or slurry from running ahead of the concrete and it forces the slurry to fill and coat the pipe walls. Without it the slurry can fall straight down not touching the pipe wall and therefore not lubricating anything.

The single biggest mistake in a downhill prime is the prime speed. If you prime too slowly the material will separate as it falls and plug the line every time. Use speed, not power to prime out a downhill system or even a boom that's aimed down. Plugging downhill is not an option since any plug will require the dis assembly of the system to clean it out. Often a downhill is in a poorly accessible location that was set up the day before the pour and/or secured to fixed objects that can help hold the system so having to wrestle downhill sections full of concrete can be quite challenging.


Because of this, use every precaution and make certain that you are pumping faster than gravity can pull the mud down the pipe. Eventually the head pressure builds up a bit from the horizontal system after the free-fall to help hold back the material in the down pipe,. Keep the speed up and throttle down.. Once the line is full, speed can be reduced but do have the crew kink the tip or use some means to stop the mud from free falling out as they stop pumping for even a few seconds. What is interesting is the obvious reduction is line surge in downhill pumping. The weight of the material helps it try to flow between pump cycles so the actual cycling of the pump is often negated by this assistance from gravity and not felt at the discharge. Its like the flow from a squeezer for those that have ever worked with one. As smooth as your 2 cylinder concrete will ever get..

The 2nd means of screwing the pooch going downhill will generate some debate and I have done it both ways with success...

Some folks believe that the solution to separation in downhill comes by simply leaving out a gasket at the top of the down-turn or using a gasket that has been cut out to allow air to pass. As material drains in the down-pipe, air can enter the system and the material drains without creating a vacuum in the system that causes the mud to separate or pull itself apart as it tries to fall.

Underwater pumping is especially difficult since the constant risk of separation exist where ever there is not concrete inside the system where water could enter. These pours have to be well planned and orchestrated in order to prevent disastrous results when working with divers.


 Boom Prime plugging...


Once again, dirty boom pipe is most often to blame. I see people suck balls back without water and want to go smack someone. How hard is it to add a few gallons of water before sticking a sponge in the tip?

The chances of a successful prime tomorrow using grout, gel or water are greatly reduced if the 5” pipe walls have a nice uniform layer of today’s concrete on them with some small rock included. The “boundary layer” as its called is the layer of material that actually contacts the pipe wall. If that wall has been reduced by a good coat of old grout or slurry from poor washouts the boundary layer forces the actual material slug to reduce in size as well.


Depending on the mix design it may not be able to do this and the result will be plugging. The same effect as trying to pump 1.5” rock thru 4” hose.

As balls or sponges travel they shrink in size and leave more and more scum on the pipe walls until the deck and turret are only 4” in some cases when pea-rock or grout was pumped in a boom. If the velocity was low, the build-up will be high. That is why anytime grout is to be pumped thru a boom it must have about 800 lbs of pea-gravel in the mix to keep the mix from building up in the boom system. That small amount of rock helps grind itself clean as it moves.


Having a dirty boom system you leave yourself open to every possible adverse condition.

If tomorrows mix just happens to be boney, or lean, and your system is dirty, then it ain;t gonna happen. When the pipes are opened to beat out the plug that will be there, everyone gets to see the heavy layers of build-up and see what a rotten washout you did yesterday and probably the previous few days as deck pipe layers are like the rings on a tree trunk. They tell the age of the problem. I do not understand why someone would suck a sponge fast or without a few gallons of water between balls (if there is risk of build-up use 2) knowing they had to pump concrete tomorrow, regardless of how good you think you are. Risk is risk, plain & simple. Lower the risk by doing known good washout procedure today and multiply your chances of success tomorrow with an easy prime. Concrete absolutely loves to slide against clean hates scraping crud off of pipe walls. Whatever loose material remains in the system will be scraped and collected as the fresh material travels and even some wet grout can plug with all this loose trash and force a dry plug in the system, boom or line pump.


Another well known cause of plugs following dirty system, is an improper prime technique with water, gel or even grout.


Lets assume the boom is clean and the mix is avg, decent 5.5sk w/1” aggregates. A decent pump mix for a 5” or even a 4.5” boom.

Water prime is common and thats what the plan is...


How do you screw this up? Quite easily actually. If you think about the cycling of your pump you understand that valve change only occurs at the end of a stroke. People have a bad habit of just spraying water in the hopper without ever looking to see where their pistons are, or when the next valve cycle will happen. THIS is the fatal mistake. If you have 10-15 gallons of water in the hopper, maybe even with gel, and start the pump midstream, you first suck in ½ stroke of water, then a full stroke of concrete, THEN more water. Now you have a full stroke of concrete with water ahead of it AND behind it. This is separation in the making.


Whats worse is the fact that it is so easy to prevent by simply cycling the pump before starting to add concrete and stopping the pump immediately after valve change in forward cycling. This assures you that the next thing the pump does is make a full stroke and load the open cylinder fully.

Add concrete so that it chases the water into the open cylinder that has the piston at the bottom and when the water covers that hole, turn the pump on so that ALL the water/gel is sucked in the first stroke and the next stroke will be all concrete as the 1st stroke of lube/primer is discharged into the rear end. Easy.

If the boom is clean there is almost no way to screw that up... Separation is the enemy here. If you get grout, getting it too thin or too wet will have the same effect and cause separation if its not introduced properly.


Now I know there will be a thousand guys read this and say BS! “I don't cycle my pump and I prime with water everyday and never have a problem” Good, I'm glad. You WILL someday. If you want to postpone that day for as long as possible, try it my way.


The method comes from over 30 years of experience in the field. Take it or leave it. Your choice.

Allowing the pump to cycle before concrete is dumped in just makes the mud and water mix and makes for a sloppy prime. It waste the customers material and makes a mess to be dumped somewhere. You can very easily waste a ½ cu yd of concrete in a sloppy prime and when you set up to do a 7 yd pour that can make or break it. Doing the prime the way I described sends ALL the water or gel first and I can start a pump and tell the hose-guy when to pull the tip hose back over the pour because I know exactly when the water will go from clear to solid concrete exiting the tip. When you learn to count strokes and know the boom angles and positions you will get good enough to close your eyes and still know exactly when the concrete first hits the ground. Because the mud's not been mixed with the prime, you waste nothing and the mess is kept to a minimum. Plug up on the prime because you created a separation issue when priming and the mess can be extensive besides having zero support from a contractor that is loosing material, time and money.


Lets say you did screw it up....What to do? Perhaps the pump stopped cycling as you primed from a loose cord or a blown fuse. Not all is lost. If the prime was done as I described, and the top of the boom was not reached yet, you can stop, let it sit for 10 minutes, do a 2 stroke reverse and go forward as usual. All you are doing is pulling what might be separated at the point where the prime and concrete meet and allowing it to return to a semi fluid state instead of the separated material that can cause the plug if moved forward. If there was material that actually flowed from the tip indicating that you reached the top, even just barely, you;re home free.


 The worst that can happen in an interrupted prime is stopping before mud gets past the turret or into the turret. It tends to separate very easily in deck pipes since they are laying down flat and the prime washes apart the bottom and fails to lube the top half of the pipe. Gently resume forward pump until it tries to hang, then back it up a couple strokes and try again. It might take several rev/for cycles but you can get it to move again as soon as lube is restored to the system.


To explore what to do “if”...

Lets go back to previous pages and apply the same principles. If the booms main, 2nd & 3rd are pointed up, 4th (5th&6th) down, and you know where its plugged because you counted strokes, you know instantly that you can reverse it hard and watch the hopper for mud rising. If it does come up, you're pulling the plug. Pull it back as far as possible and then drop the power and gently move it forward. The pump is not pulling the mud, the concrete is. As the mass moves backwards it keeps the “slug” intact and pulls itself back. If its forced to separate that is because the plug is jammed tight and has not moved yet. A familiar term. Loss of lubrication.


Whether it be separation or a lean mix its still loss of lubrication that caused the mud to stop moving. By reversing and moving forward the “good” material is bringing more lube (cement/water/slurry) to the plug and pressing it into the dry slug. As its reversed it tries to break the plug apart making the next forward push more successful in bringing lube to the front of the slug. Never beat on a plug in ANY pump. That's begging for a system failure and possibly injury. Who is going to get nailed by the flying debris is any ones guess. Rest assured whoever it is has probably seen a 1-800 SUE-YOU2 television commercial.

That's what the pump company was looking for....another lawsuit. That's not what you want them to remember when your review comes around for pay raises or bonue's.


Don't beat on the plugs...


If you are sure the plug is in the downhill run of the boom, there is likely more to it than loss of lube. There could be a clinker, old build up, sometimes something that came down the chute. I've seen a dead rabbit plug up a boom...a floor mat, a hammer, pieces of conveyor belt, a tooth off a loader bucket and just about all other things you can imagine. They usually happen on the downhill because as long as they are under pressure they will remain contained in the center of the traveling concrete slug. As they free-fall the downhill boom sections they tend to hit the next elbow that stops the fall and they sit there and get beat into a plug since they are not a source of lube to the material. Knowing that we cannot suck concrete uphill as we described in the above section on trailer pumping, what are the options?


The most obvious is to break it open. Resist the urge and think about this before acting. As soon as you pop a clamp you have disconnected your best tool from the problem. The pump. If you start opening pipe system there is nothing that the pump can do to help you, so save that move as a last resort. If you bust open a pipe to find a plug you also separate yourself from the functional part of the pump that is filled with concrete and requires your attention as much as the plug does. Why not keep in touch with both and use one to work the other?


The first choice would be to use whats at your disposal, the power of the pump and gravity. Look for a place where you can swing around and stand the boom straight (or just upward) and reverse it to help pull the plug back. Again, know the strokes and where you are. Know the signs of mud moving back or not. Gently go forward and be extremely careful because you might actually succeed and there could be rocks and falling debris from the tip hose that's anywhere from 100 to 200 ft over the ground. That's why we swing around and get it away from the crew and property that would be damaged by falling debris.


If this does not work and you've decided that the plug is near the tip, then use this vertical position to suck back as much as possible so that if you have to open the boom there won;t be a flood of mud draining on top of you and where you do this.

Look to the tip elbows. That's the last chance for a boom to plug and often where it happens since the boom jib is long and the falling concrete often does separate during that free-fall. If you have a reducer hanging, that's the likely spot since mud loves to separate before it tries to reduce after a long free-fall. Concrete that is not well mixed and lubricated does not reduce...ever.


If you did hang a reducer, always open the small end first, and use a stick or something to poke in there (not your hand or face) and see if there is a plug there before popping the big end that might have a bunch of material stacked on top of it waiting to find a way your face. You only get the pair of eyes that you came with..


Sometimes you get lucky and find a minor plug (because you did not beat on it and make it worse) in the tip elbow that can easily be beat out with a hammer hitting the ring on the elbow or the clamp. I mention this “ring” because hitting a dual-wall elbow in the radius or anywhere else that has a liner will result in its eventual failure and cause premature wear and blowing. The purpose of these expensive pipe sections is to extend wear and coincidentally safety, but beating them causes damage that ends up costing the company more money that they would have gladly given to you as a reward for exceptional performance and for taking care of their machine.


They're (the company elders) going to spend the money. They can spend it on you or the pump. The operator always decides which. They simply observe your decision over the course of the year...


Things to remember about plugging...


Anytime a plug has to be removed by opening the system, prime/slurry must be replaced to travel ahead of the remaining concrete or a loss of lube condition will cause another plug. You gain nothing by trying to skip this step, except anger and frustration that will cloud your judgment further. Act intelligently and think it thru before acting.


Plugs are accompanied by a rapid build-up of pressure behind the plug or between the plug and the pump. Relieve that pressure before opening any coupling and attempting to clear a plug.


Loss of lubrication can often be prevented by stretching what cement or cement compatible materials are there with water. Primers are usually not welcome in foundations and especially unwelcome in walls and columns. Properly priming procedure reduces the waste and utilizes the maximum amount of delivered material. Avoid the prime and material mixing by use of good pump priming technique.


Pay attention to whats going in the hopper and how the concrete is discharging from your system. A sudden stop in falling material from a boom tip hose with the pump still running signals a plug that’s solid and you only have 1-2 heartbeats to stop the pump before it pressures out and fills the boom with high pressure and possibly causes a pipe to blow or a coupling to break. Be “on the button” at all times and do not allow yourself to be distracted by conversation or other activities. Stay focused. There is no room for the “walk & chew gum” debate here. Do that later when other peoples money or life is not at risk from your distraction.


The key to successful concrete pumping is knowledge and good judgment. Since I cannot describe each and every possible scenario and tell you how to escape unscathed, I have to provide the information necessary for you to process, learn and be able to make your own decisions and develop the kind of skills that can only come from experience. This is not intended to be a “how to” instruction, but more of how and why and what can be done. You decide. In learning these things that we've discussed here, you now have the tools that can be used to make good, solid decisions and that can be your source of power in dealing with the things that can happen during the course of your career in pumping. Use it and pass it on.

Next Chapter:

Plugging in the cylinder and concrete valve/rear end.


By Lee Horton
Published by
All rights reserved.


Telealbelt 07-22-2011
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I have to think about how I learned 25 years ago and how helpful this info would have been. Excellent job Lee.

MVCP 07-22-2011
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Great info!!!! I will print this one out. Thanks Lee

WgtnPumps 01-25-2019
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Amazing info, thank you so much for sharing! Todd your link no longer works - can we access the rest of this somewhere else these days? Cheers

SUPERDOFFER 01-27-2019
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I remember in the beginning of this site there where a lot of these helpful articles on here.

But that was the time the site was for pumpers and not for sponsors.

In these days experienced pumpers took the time to answer questions of newbies, but I think they all left the site.

My advice for the Newbies, start reading on page 1

mcratchet 01-29-2019
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I cant open the link on chaper one is this the continuous from the one that was posted in 2011?

SUPERDOFFER 01-30-2019
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mcratchet i think you mean this post


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..

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.

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


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


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.


WgtnPumps 02-02-2019
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Thank you SO much these are gold

WgtnPumps 02-02-2019
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Is this from a book you can buy?

mcratchet 02-05-2019
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