Fresh Water Pumps - Vertical Turbines
Vertical Turbine Pumps are used in a high number of municipal water systems for fresh water processing.
Vertical turbines are commonly used in all types of applications, from moving process water in industrial plants to providing flow for cooling towers at power plants, from pumping raw water for irrigation, to boosting water pressure in municipal pumping systems, and for virtually every other imaginable pumping application. Turbines are one of the most popular types of pumps for designers and end-users.
A.R.&E. is an EASA (Electrical Apparatus Service Association) member and an "EASA Accredited Service Center". As such we have at our disposal, the full engineering staff of EASA Headquarters. I mention this here as a preface to offering you access to an article in "Pumps & Systems" magazine that was written by Eugene Vogel, one of the EASA Staff Engineers. You can click this link to be taken to that website article on Vertical Turbines. It's well written, and very informative.
But what is a "vertical turbine" pump? These pumps are "LONG"! And depending on their capacity, i.e. GPM and TDH specs... they can be outright
monstrous in size.
They are designed with the suction end connected to the prime mover, typically an electric motor, by way of a
long drive shaft enclosed by the delivery pipe for the pumped liquid. The exterior delivery pipe is usually multiple flanged sections of varying lengths, but sometimes the
sections are "threaded together", depending on the
manufacturer and the final installation environment. The drive shaft is made up of a number of "sections", threaded on each end and connected together with threaded couplings.
Designs vary but this drive shaft may be totally "enclosed" by another tube, or it may actually be in the stream of the pumped liquid. When it is enclosed, the bearings may be
lubricated by an external water source or they may be grease or oil lubricated. When the shaft is "open", the bearings are lubricated by the liquid being pumped. Bearings are
"sleeve" bearings and depending on the manufacturer and environment may be made of steel, bronze, rubber, nylon, or other man-made materials. Each bearing is supported within
the outer pipe by a "welded in place" web design. These supports are typically placed every 3 to 5 feet. Since we're talking here about "sleeve" bearings, we must understand
that any "thrust" created by the pumping action, plus the weight of all the impellers and drive shaft, must be borne by the bearings of the prime mover.
So
what's the real magic in vertical turbines? I'm not sure it's actually magic, but it's pretty cool anyway... We talk about the "stages" or "bowl assemblies". The magic happens
when you "stack" bowl assemblies in a vertical turbine. The actual "pumping technology" happens based on the design of the impeller and bowl assemblies. As
the impeller spins, it draws water into it's lower mouth (the suction case) and based on pure hydraulic dynamics, gets forced to the outside of the spinning circle and up toward
the outlet
diffuser. In doing so, the laws of physics turn the mechanical energy into pressure and the pressure "increases". So if we design a "bowl assembly", capable of pumping 1000 GPM
(gallons per minute) at 100 Ft TDH (Feet Total Dynamic Head) and use it as a "Single Stage Pump", we'll be able to pump 1000 GPM against a 100 ft head. Meaning we can push the
water 100 feet up the hill. Now, let's stack a second bowl assembly on the column. We now have a "Two Stage Pump". But the magic is that while we can still only pump 1000 GPM,
the outlet pressure has been DOUBLED, so we can now pump the water a full 200 feet! Pretty amazing, right? And we've seen three, four, or five stage pumps in the shop.
So remember, when it comes to the Vertical Turbine, the designed GPM pumping capability has nothing to do with number of stages, but instead with the diameter and design of the impeller and bowl assembly. And the number of "bowls" or "stages" is what determines the total lift ability or TDH the pump can push water against. When it comes to "moving water", a municipal system has to process a lot of water to keep it's inhabitants happy. So the vertical turbine is a true solution to the problem of pulling water out of the river and pumping it up the hill to the processing plant where it is cleaned, filtered, and distributed to the town folks. We used an example above of pumping 1000 GPM. That's a drop in the bucket compared to some designs. Vertical turbine pumps have been designed to provide 25 or 30 THOUSAND GPM. And in extreme cases... over 100,000 GPM. That's a lot of water! Know your needs... before making your final decision on the pump design for your project.
Impeller Design
The "bowl assembly" (referred to as a "stage") is the working section of the vertical turbine and therefore considered the most important. Within that "bowl assembly" is the impeller which moves the water and causes the pump to actually be useful. Some general questions need to be addressed about the impeller and we'll touch on a couple of the most important ones here.
There are basically 3 types of impellers associated with the pumps; Open, Semi-Closed and Closed. Each has a purpose and your selection of one versus the other is critical to both the efficiency of the pump and your project's success. Another important factor of the impeller is the material of which it is made. So let's talk about the "type" first. And while the photos below are NOT necessarily indicative of a "vertical turbine" pump, they do show the design differences of the 3 types.
An OPEN impeller has vanes that are attached to the center hub and mounted directly to the rotating shaft. There is NO backing plate or "wall" surrounding the vanes which contributes to the open impeller being weaker than it's other 2 counterparts. An open impeller can handle "suspended" solids and is less susceptible to "clogging". If it does clog, it's pretty easy to clean and make operational again.
A SEMI-CLOSED (or semi-open) impeller will have a backing plate on the "back" side of the vanes which adds significant strength to this type impeller. These impellers are typically used to pump liquids with solids. And while efficiency is a common problem, the ability to pass solids balances out that issue.
The CLOSED impeller has a plate on both the back and front of the vanes. This makes it the "strongest" type of impeller, from a physical strength standpoint. Because of the "totally closed" nature of the vanes, this type of impeller is best used in applications that are pumping "clear" liquids. Although, in larger pumps, due to the physical size, liquids with "suspended" solids can be moved successfully. That having been said, the "closed" impeller does not work well with solids and are difficult to clean, should they become clogged.
Impeller Material
The material of which the impeller is made is as critical as the design. This particular topic has more to do with "Fresh Water" than other liquids. But think about other applications for Vertical Turbine pumps other than "clean", "fresh" water. Maybe pumping a slightly caustic or acidic liquid using a pump with brass impellers may shorten the life of the pump assembly. And even the pumping of "clean" water... actually how "clean" is the water being pumped out of the river? There will probably be sand, silt, and other debris that gets through the suction screen and into the impellers. Sand is not compatible with softer materials like brass or bronze. Cast Iron may be the solution here. So impeller material IS an important factor and should certainly be considered when selecting your "perfect pump". And make certain you do some research into the actual makeup of the liquid you're going to be pumping before you finalize your vertical turbine selection. Better safe than sorry!!!
Installation and Removal
One final note on this design is that when selecting a Vertical Turbine as your pumping solution, keep in mind that you've got to have a mechanical room with a VERY HIGH CEILING and usually a "wet well" pit or holding tank into which the vertical bowl assembly (working portion of the pump) will reside. The top of the pump will usually have a large bed plate (maybe 36" to 48" square) depending on total pump size. The pump column with the turbine stages will hang from this plate. The plate will be mounted over a hole in the floor of the mechanical room over the "wet well" pit. This takes care of the pump, but now you have the electric motor (or right angle gearbox for a diesel engine) sitting on top of the bed plate, as well as the discharge piping from the pump. Depending on horsepower and speed, the motor may be 4 or 5 feet tall. Put all this together as a complete assembly and you may have 40 feet or more of equipment.
So how do you install and remove a "pump assembly" that's 40 combined feet of machinery? And you know it's going to have to be removed at some time for maintenance or upgrades. First of all you've got to have access to the building with a crane. Make certain you've got easy and safe access to the area. Cranes today can reach and lift some really awesome loads, but you still have to plan for their access. Then, do you cut a hole in the roof of your building or are you going to have to disassemble the pump "on site"? Disassembling on-site still requires crane access because each piece you remove is going to be heavy. Maybe you install an internal, overhead crane, within the building. That'll work, but now move those pieces from the working area to a loading dock where you can load them on a vendor's truck for transport to some repair facility. Think about it NOW!!! Because when it comes time to remove the pump, it would be a whole lot better to have had any access holes designed into the building in the beginning rather than when you're under the gun to get things out, and back in, during an emergency breakdown.
Call on A.R.&E. for help with any of your questions. We've been through a lot of different scenarios with rigging pumps in and out of our customer's facilities, and maybe we haven't seen them all, but our technician's experiences will help you make the right decision when it comes to selecting your "perfect pump".
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