This is the West Closure Complex, a billion-dollarÂ
piece of infrastructure that protects parts of New  Orleans from flooding during tropical storms.Â
Constructed partly as a result of Hurricane  Katrina, it features one of the largest pumpingÂ
stations in the world, capable of lifting the  equivalent of a fully-loaded Boeing 747 everyÂ
second. When storm surge threatens to raise  the levels of the sea above developed areasÂ
on the west bank of the Mississippi River,  this facility’s job is to hold it back. The gatesÂ
close and the pumps move rainwater and drainage  from the City’s canals back into the MississippiÂ
River and out to the gulf. This pump station may  be the largest of its kind, but its job is hardlyÂ
unique. We collectively move incredible volumes  of fresh water, drainage, and wastewater into,Â
out of, and around our cities every day. And,  we mostly do it using pumps. I love pumps. But,Â
even though they are critical for the safety,  health, and well-being of huge populations ofÂ
people, there are a lot of things that can go  wrong if not properly designed and operated.Â
I’m Grady, and this is Practical Engineering.  In today’s episode, we’re exploring someÂ
of the problems that can happen with pumps. This video is sponsored by HelloFresh,Â
America’s number 1 meal kit. More on that later. I’ve got some colored water and clear pipe outÂ
here in my garage to demonstrate a few common  pitfalls that pumps can face, and the firstÂ
one is priming. Although liquids and gases  are both fluids, not all pumps can move themÂ
equally. Most types of pumps that move liquids  cannot move air. It’s less dense and moreÂ
compressible, so it’s often just unaffected  by impellers designed for liquids. That has a bigÂ
implication, though. It means if you’re starting a  pump dry - that is when the intake line and theÂ
housing are not already full of water, like I’m  doing here - nothing happens. The pump can runÂ
and run, but because it can’t draw air out of  the intake line, no water ever flows. This is whyÂ
many pumps need to be primed before starting up.  Priming just means filling the pump with liquidÂ
to displace the air out of housing and sometimes  the intake pipe. Watch what happens when I raiseÂ
the discharge line to let water flow backwards  into the pump. It happens quickly. As soonÂ
as the air is displaced from the housing,  the pump is primed and water starts to flow.Â
There are a lot of creative ways to accomplish  this for large pumps. Some even have small primingÂ
pumps to do this very job. “But what primes the  priming pumps?” Well, there are some kinds ofÂ
pumps that are self-priming. One is submersible  pumps that are always below the water whereÂ
air can’t find its way in. Another is positive  displacement pumps that can create a vacuum andÂ
draw air through. They may not be as efficient or  convenient to use as the main pump, but they workÂ
just fine for the smaller application of priming. However a pump is primed, it’s critical thatÂ
it stays that way. If air finds its way into  the suction line of a pump, it can lose its primeÂ
and stop working altogether. When I lift the pump  out of the water, the prime is lost. And nowÂ
if I put the pump back down into the water, it  doesn’t start back up. This can be a big problemÂ
if it goes unnoticed, not just because the pump  isn’t working, but also because running a pumpÂ
dry often leads to damage. Many pumps depend on  the fluid in the housing for cooling, so withoutÂ
it, they overheat. In addition, the seals around  the shaft that keep water from intruding on theÂ
motor depend on the fluid to function properly.  If the seals dry out, they get damaged andÂ
require replacement which can be a big job. The next problem with pumps is also related to theÂ
suction side. Pumps work by creating a difference  in pressure between the inlet and outlet. In veryÂ
simple terms, one side sucks and one side blows.  A problem comes when the pressure gets too low onÂ
the suction side. You might know that the phase  of many substances depends not just on theirÂ
temperature, but also on the ambient pressure.  That’s why the higher you are in elevation, theÂ
lower the temperature needed to boil water. If  you continue that trend into lower and lowerÂ
pressures, eventually some liquids (including  water) will boil at normal temperatures withoutÂ
any added heat. It’s a pretty cool effect as a  science demonstration, but it’s not something youÂ
want happening spontaneously inside your pump.  Just like they don’t work with air, mostÂ
pumps don’t work very well with steam either.  But, the major problem comes when those bubbles ofÂ
stream collapse back into a liquid. Liquids aren’t  very compressible so these collapsing bubblesÂ
send powerful shockwaves that can damage pump  components. This phenomenon is called cavitation,Â
and I have a video covering it in a lot more  detail that you can check out after this one toÂ
learn more. It usually doesn’t lead to immediate  failure, but cavitation will definitely shortenÂ
the life of a pump significantly if not addressed. The solution to this problem at pumpsÂ
is known as Net Positive Suction Head,  and with a name like that, you know it’sÂ
important. Manufacturers of large pumps will  tell you the required Net Positive Suction HeadÂ
(or NPSH), which is the minimum pressure needed at  a pump inlet to avoid cavitation. The engineer’sÂ
job is to make sure that a pump system is designed  to provide at least this minimum pressure. ThatÂ
NPSH depends on the vertical distance between  the sump and inlet, the frictional losses inÂ
the intake pipe, the temperature of the fluid,  and the ambient air pressure. Here’s an example:Â
With this valve wide open, the suction pressure at  the inlet is about 20 kPa or 5 inches of mercury.Â
Now watch what happens when I move the pump to the  top of the ladder, but leave the bucket on theÂ
ground. The suction pressure just about doubles.  A constriction in the line also decreasesÂ
the available NPSH. If I close this valve on  the intake side of my pump, you immediately seeÂ
the pressure in the line becoming more negative  (in other words, a stronger vacuum). ThisÂ
pump isn’t strong enough to cavitate,  but it does make a bad sound when there isn’tÂ
enough Positive Suction Head at the inlet.  I think it easily demonstrates how aÂ
poor intake design can dramatically  affect the pressure in the intake lineÂ
and quickly lead to failure of a pump. The last problem that can occur atÂ
pumps is also the most interesting:  vortices. You’ve probably seen a vortex form whenÂ
you drain a sink or bathtub. These vortices occur  when the water accelerates in a circular patternÂ
around an outlet. If the vortex is strong enough,  the water is flung to the outside, allowing air toÂ
dip below the surface. This is a problem for pumps  if that air is allowed to enter the suction line.Â
We talked a little about what happens when a pump  runs dry in the discussion about priming, butÂ
air is a problem even if it’s mixed with water.  That’s because it takes up space. A bubbleÂ
of air in the impeller reduces the pump’s  efficiency since the full surface of the bladesÂ
can’t act on the water. This causes the pump to  run at reduced performance and may causeÂ
it to lose prime, creating further damage. The easiest solution to vortexing is submergenceÂ
- just getting the intake pipe as far as possible  below the surface of the water. The deeper itÂ
is, the larger and longer a vortex would have  to be before air could find its way into the line.Â
This is achieved by making the sump - that is the  structure that guides the water toward the intakeÂ
- deeper. That solution seems simple enough,  except that these sumps are often major structuralÂ
elements of a pump station that are very costly to  construct. You can’t just indiscriminatelyÂ
oversize them. But how deep is deep enough? It turns out that’s a pretty complicatedÂ
question because a vortex is hard to predict.  Even sophisticated computational fluid dynamicsÂ
models have trouble accurately characterizing  when and if a vortex will form. That’s an issueÂ
because you don’t want to design and construct  a multi-million-dollar pumping facility justÂ
to find out it doesn’t work. And there aren’t  really off-the-shelf designs. Just about everyÂ
pumping station is a custom-designed facility  meant for a specific application, whether it’sÂ
delivering raw water from a reservoir or river  to a treatment plant, sending fresh water outÂ
to customers, lifting sewage to be treated  at a wastewater plant, pumping rainwaterÂ
out of a low area, or any number of other  reasons to move large volumes of water. SoÂ
if you’re a designer, you have some options. First, you can just be conservative. We knowÂ
through lots of testing that vortices occur  mostly due to non-uniform flow in the sump. AnyÂ
obstructions, sharp turns, and even vertical walls  can lead to flow patterns that evolve intoÂ
vortices. Organizations like the Hydraulic  Institute have come up with detailed designÂ
standards that can guide engineers through the  process of designing a pump station to make sureÂ
many of these pitfalls are avoided. Things like  reducing the velocity of the flow and maintainingÂ
clearance between the walls and the suction line  can reduce the probability of a vortex forming.Â
There are also lots of geometric elements that  can be added to a sump or intake pipeÂ
to suppress the formation of vortices. The second option for an engineer is toÂ
build a scale model like I have here.  Civil engineering is a little bit unique fromÂ
other fields because there aren’t as many  opportunities for testing and prototyping.Â
Infrastructure is so large and costly,  you usually only have one shot to get the designÂ
right. But, some things can be tested at scale,  including hydraulic phenomena. In fact, thereÂ
are many laboratories across the world that  can assemble and test scale models of pumpÂ
stations, pipelines, spillways, and other  water-handling infrastructure to make sure theyÂ
work correctly before spending those millions  (or billions) of dollars on construction. TheyÂ
give engineers a chance to try out different  configurations, gain confidence in theÂ
performance of a hydraulic structure,  and avoid the pitfalls like loss of prime,Â
cavitation, and vortices at pump stations. It’s time for everyone’s favorite segment of  me trying to cook while my wifeÂ
tries to capture that on video. “Don’t mind if I just groundÂ
some espresso in the background.” Goofing around in the kitchen isÂ
one of our favorite things to do  together. That’s why we’re thankful forÂ
HelloFresh, the sponsor of this video,  for converting cooking from a chore intoÂ
our favorite thing to do on date night. “How geometrically pleasing to the eye...” We are indecisive eaters, meaning neither of usÂ
likes to be the one to decide what’s for dinner.  It’s nice to have HelloFresh curating deliciousÂ
and healthy recipes so we don’t have to. “Don’t mash it.” The pre-portioned ingredients mean there’s lessÂ
prep and less food waste, and the packaging is  mostly recyclable or already recycled content.Â
HelloFresh also helps us get dinner ready quickly  when we don’t feel like planning, prep, andÂ
shopping which is pretty much every day right now. [Miscellaneous baby noises] Go try it yourself at HelloFresh.com and use  code PRACTICAL12 to get 12 freeÂ
meals, including free shipping. “Youre mashing it… just throw that one in there.” Supporting our sponsors helps support thisÂ
channel. That’s HelloFresh.com and use code  PRACTICAL12. Thanks, HelloFresh, and thankÂ
YOU for watching. Let me know what you think.
I love pumps!
I've seen the aftermath of the death of a pump. It was almost like a god honest crime scene investigation.
What had happened was a large feedwater pump which had suddenly, for unknown reasons, lost all pressure on the suction side. These pumps are usually lubricated by whatever flows through them, although the bearings are on a separate oil lubrication loop. Now, when a high pressure, high volume pump like that loses lubrication, it's going to seize in a matter of seconds or minutes at most. It did but its motor did not. I don't remember what the power output of the motor was, but it's easily in the 200-400 hp range.
Between the motor and pump shafts is an alignment coupling, a lump of steel and bolts of approx 45 lbs mass. That sucker had detached and flung into the ceiling with enough force to tear out an entire pipe gallery and caused thousands in damages, not to mention the pump itself, valued at at least $150,000 was a complete write-off.
Another time was an enormous sewage pump which had seized because of an internal blockage (debris in the waste water). It was connected to a motor which sat at a considerably higher level, driving the pump through a long shaft with a set of U-joints. The pump-side U-joint had failed, but the engine-side joint held, basically turning the remaining shaft into a humongous flail which had destroyed everything inside the pump well.
Love this guy. Voice is so soothing and he is hella smart.
Practical engineering is an excellent channel
damm thats a lot of issues. then imagine how hard it must be to replace our heart with something mechanical..
Very nice video!
This video pumped me up.
Idk. This guy says “he loves pumps”, but something is telling me he is throttling a certain anti-pump propaganda. I wouldn’t be so certain that he loves pumps. If he did love pumps, why didn’t he install just as powerful of a pump himself? I mean, I wouldn’t say I love pumps, but c’mon right? At least I’m good at priming his mom’s pump when she needs it. Anyway, it’s not the actual machinery of the pumps in the first place, it’s the pumps themselves that keeps it going forward. I’m just not sure this guy loves pumps is all. As he said, “one side sucks and one side blows,” so he doesn’t seem that happy in his relationship with pumps.
whoa for a sec there I thought I miss clicked on a Lockpickinglawyer vid.