Pumps and Pump Stations
|By Igin Staff|
In the movie THE WIZARD OF OZ, the Tin Man was lacking something; it seems the tinsmith had forgotten to give him a heart.
Here in the real world, of course, no ‘man’ could exist without a heart, much less dance down a yellow brick road. Without a central pumping station in good working order, a living body dies.
The same is true of many irrigation systems. In the past, irrigation designers and contractors may have been able to design and build systems that didn’t need an extra boost from one or more pumps, because plenty of pressure came out of the municipal water system. But today, an irrigation contractor needs to be familiar with pumps and pumping stations.
Pressure drop There are a number of reasons for this. Mainly, it’s that water, and water pressure, just can’t be taken for granted anymore. Growing populations bring an increased demand for potable water. This has lowered the water pressure in many areas, necessitating a need for a boost. And there are other challenges as well.
“Nowadays, it’s getting to the point where cities are providing, as we jokingly say, just enough pressure to get water into a fire hydrant,” said David D. Davis, an irrigation consultant and principal of David D. Davis and Associates in Arrowhead Highlands, California. “That doesn’t include the sprinklers or faucets in a house (or building). So then, the owner of that property has to add a pump to deliver water anywhere else that he needs it.”
Davis says this is partly because of the buildout of residential areas, and partly because “people want homes that sit on top of hills, because they have views. If I own a large home on top of a hill, I might have to install a pump to push that water up to my house.”
If there is any elevation on a residential or commercial site, the first thing you need to do, according to Davis, is a pressure test. Go to the closest fire hydrant and get the information off of it. Or, call the fire department and have them read you the pressure it’s been tested for. You can also call the local utility district. They can tell you that ‘at the corner of Elm and Maple, there is X amount of pressure.’ Most cities keep track of this information.
“You take a look at that pressure, and if you’ve got less than 50 pounds per square inch (psi), immediately plan on a pump,” said Davis. “A 50 psi reading, with not too much of an elevation, would run spray heads and drip irrigation systems, but it wouldn’t necessarily run bigger rotary-type sprinklers.”
“As we lose surface water, municipalities are increasingly unable to get enough infrastructure. They’re building two-part systems; one, a potable system, and two, a nonpotable system for irrigation,” said Andy Schoenberger, product manager for Franklin Electric, the Bluffton, Indiana company that makes Little Giant pumps.
As construction moves further out from city limits and into the foothills, cities are less able to get water out to the newer subdivisions. Pumps are then needed to draw water from nearby lakes, streams and wells, or from graywater or rainwater harvesting systems.
Paul Layshock, vice president of Cary, Illinois-based Naturescape Design, has seen this happen. He says, “In Illinois, it’s not so hilly, but we have the same kind of situation with the municipalities. They have grown over the years, and their demand for water is such that pressures have been reduced.”
“So, you can have a large irrigation system where you’ve got to have 40, 50, or 60 gallons per minute (gpm), and the pressure is just not there to run it,” says Layshock. “Now, any time you have a commercial project, even a small to mediumsized one, you really need a booster pump.”
What kind of pump?
Now that you’ve determined that you need a pump or pump station, how do you determine what type to buy?
Unfortunately, there’s no onepump-fits-all solution. “All pumps aren’t created equal,” said Rick Heidvogel, sales manager for Watertronics, Inc. in Hartland, Wisconsin.
“There are hundreds of different pump types for different uses.”
Contractors dealing with turf in the North American market are almost exclusively going to be using horizontal (motor laid on its side) end-suction, vertical multistage, vertical turbine or vertical submersible pumps. Most likely, you’re going to be installing a horizontal end-suction booster pump. That’s the kind most often used in residential or commercial turf applications. These are used for taking a municipal water supply coming in at 29, 40 or 60 psi, and boosting it to 40, 60 or 80 psi, to produce enough pressure to meet the factory specifications to operate rotors or spray heads.
“People will ask me, ‘What’s the best, most efficient type of pump?’” said H. Rex Hansen, P.E., pump station sales manager for Azusa, California-based Rain Bird Corporation.
“I’ll say, ‘Vertical turbine.’ But you hardly find applications for vertical turbines in turf. You need wet wells to run them.”
If you’re going to be pulling water out of a nearby creek, pond or lake bed, a submersible pump may be just the ticket. However, “submersibles have the worst efficiency,” says Hansen. “And they’re hard to service, because you have to pull all the pipe out.” But if you need one, you need one. You’re also going to need a sediment filter to get the silt and nutrients out that can clog spray heads.
Many times, it is more than just a pump that you need. It is at those times when it might make more sense to get a pump station which can be ordered off-the-shelf, or you can have one custom-built. It’ll be assembled and tested at the factory, then delivered as a package on a skid.
A pump station is comprised of one or more pumps, mounted on a metal deck with plumbing. It could be enclosed to house the pump(s), filter, control valves, pressure relief valve, and the electrical control panel. Some more expensive systems have digital displays, and sometimes, touchscreen controls.
To determine what size or horsepower of pump to order, you first need to figure out the “duty point” of your system. That’s the combination of the pressure and the flow. To determine that, you look at the most demanding zone that you’re going to irrigate.
Let’s say that you’ve determined that you need X amount of flow, going through a one-inch valve, at 25 gpm at 50 psi. That is your preliminary duty point. You need 50 psi, but the municipal water supply will only give you 25 psi. Subtract what you’re getting from the municipality, 25, from the number you actually need, 50. Fifty minus 25 equals 25. That means you’ll need a boost of 25 psi to give you the 50 psi you need. The result is your actual duty point, 25 gpm at 25 psi.
Irrigation manufacturers and distributors have charts that will show you what horsepower pump you’ll need to supply your system’s needs, whether that’s ¾ hp on up to 60, or even higher, to get you to your duty point.
You also need to consider what kind of power is available. Is it a typical residence with 120-volt and 220- volt, single-phase power? Or a commercial site with 240-volt or 480-volt, three-phase operation? “That is a limiter,” says Heidvogel, “because not all pumps have dualpower capability.”
Variable Frequency drive (VFD)
When you’re dealing with pumps, you should know about Variable Frequency Drive (VFD). Simply explained, this controls the speed and torque of the motor by varying its input voltage. Fixed-speed motors lurch to life with high starting torque, and can experience current surges up to eight times the full-load current. VFDs instead gradually bring motors up to operating speed. This gentler ramp-up lessens mechanical and electrical stress, thus reducing maintenance and repair costs. It also saves energy. Pumps with VFD cost a lot less to run.
The most important thing?
What’s the most important consideration when choosing a pump or configuring a pump station? According to Davis, it’s “Whoever has the best field service. Preferably they’re local, with a service facility within a hundred miles (from the site).”
Layshock agrees. “It comes down to reliability and service. Pump stations are more complicated than they used to be, so getting the technical support that you’ll need is vital. Especially with today’s VFD pump stations, you really need someone knowledgeable about those systems. If something goes wrong with a VFD, it’s more technical than most irrigation contractors can work on themselves.”
Local service is important especially if the contractor is going to be doing maintenance on the system. For instance, in the Midwest, where Layshock works, pump stations have to be winterized. “We’ll take the suction pipes out of the lake or pond, and put them on the shore.”
He continues, “You have to make sure to cover the ends of those pipes, ‘cause little critters will make their winter homes in them. And if you don’t clean those out in the spring, or at least take a look in there before you put things back together, you’ll find yourself sucking a mouse or a squirrel into the pump station. Then you’ve got to take off the bolts and clean it up. It’s quite the mess.”
And apparently, size matters. “The one mistake that we see a lot is when people try to cut costs and undersize the pump, when the properly-sized pump was only about 50, 100, or 200 bucks more,” said Schoenberger. “That’s unfortunate for the project, as well as the end user. They don’t get what they need, and then people get a bad taste in their mouth, thinking it’s the product’s fault. They had the right product, it just wasn’t sized correctly.”
Halford, irrigation manager for Enviroscape, Inc. in Mechanicsville,
Virginia, really likes having touchscreen controls at the pump station
itself, as well as web-enabled remote monitoring capability. “One of our
big sites is an hour’s drive away, but I can get on my laptop and view
past historical data, graphs of flow and pressure, or see if any alarms
have gone off. I can deduce what may have happened before I get there,”
he said. He can also get texts on his smartphone that tell him if any
alarms have been tripped.
A complicated business
Building a pump station can get complicated. Once the concrete base is poured and the station is being in stalled, it is the wrong time to discover that you’ve bought the wrong things. And the larger the system, the more variables there can be in a configuration. If you’re the one responsible for choosing the components and you’re new at this game, you might want to seek the help of an irrigation consultant.
Fortunately, pump manufacturers and their representatives are very helpful. Says Schoenberger, “We work with everybody in the chain, municipalities, contractors, installers and whoever’s buying from us, with our technical support group and our field support technicians as well as online. We can assist with the project from beginning to end.”
“Be prepared,” advises Halford, “with information about what you’re about to install, so that when things get turned sideways, you have some wiggle room to work your problem out. Don’t have tunnel vision and just do a read-the-manual-and-install-the-station.”
He cites this example. “The first couple of stations I installed were shipped with drop pipes (pipes that come out of a pump station and get buried underground) with standard flanged fittings. Well, when you bolt a plastic flange onto a metal flange, it isn’t the strongest of connections. We had a couple of minor leaks that showed up as major pressure losses, because they were right at the station.”
Halford asked that in the future, the flanges be omitted and that all drop pipes be shipped with plain ends. “This allowed us to put sleeves made of ductile iron over the ends. These are a bit more forgiving than bolted-on flanges.”
As water, and water pressure, grows scarcer, pumps and pump stations will increase in importance. As a contractor who’s not already experienced in this area, it’s time to pump in some knowledge. Because chances are, you’ll be installing one soon.