Knowing some of the common challenges associated with electric submersible propeller pumps and understanding how to solve them can open companies to a different type of application than they have ever considered before. This knowledge can save them money and make it easier to maintain the equipment.
Marc Boudet has been working with MWI Pumps for more than 37 years, and said he likes to tell his customers that he is selling them water, not pumps. Therefore, it’s important for them to understand the most efficient and economical ways to pump that water.
Boudet describes the top four common challenges he faces when educating customers about electric submersible propeller pumps.
1. Educating the customer on the ease of maintenance
With some vertical pumping applications, when a pump requires maintenance the entire pump must be retrieved and dismantled. A 42-inch line shaft pump weighs more than 20,000 pounds, Boudet explained. “If you have to reach over the top of the station to get the pump out and take the gear and motor out, that’s a big job,” he said. “With a submersible electric, you take the lid of the can off and pull out a 5,000-pound pump with an A-frame hoist or a gantry crane. The ease of maintenance is that you are only pulling out the pump with the motor, and not taking out the entire column and line shaft along with everything else.”
With electric submersibles, the shaft is about 4 or 5 feet long, and there are no issues of shaft whip or wear on bushings like in a line shaft pump. From a maintenance standpoint submersible electric propeller pumps are much simpler to maintain because a complete dismantling is not necessary.
For example, a pump station in Louisiana has 4 pumps. It installed 900 horsepower motors that are on an above base discharge. The discharge has a 66-inch elbow. From the base plate to the top of the elbow is more than 7.5 feet. The motor is on top. The motor from the top to the base plate is 18 feet. A platform must be built around the motor to be able to do any work on the equipment. When there was a problem with the motor it required two days to take the platform down and retrieve the motor. By contrast, MWI could have supplied the customer with electric submersible propeller pumps. The pump installation would require only 15-30 minutes.
2. Spare parts availability and cost
Many original equipment manufacturers build custom-sized parts so that there is no option but to purchase the overly-priced parts directly from them. Their shafts, bearings, and seals all have very odd sizes. The lack of parts options makes them much more expensive.
In Key West, Boudet said he had a customer who needed to replace some mechanical seals for 20-inch stainless steel pumps that cost $15,000 from the manufacturer. They are replacing them with MWI electric submersible pumps, the cost was only $700 for the same part when required, because they are a standard size and could be purchased from a local supplier.
3. Installation choices save construction costs
The electric submersible propeller pumps can be installed vertically, horizontally, or at an angle. Therefore, a low-profile pump station can be built. For example:
At a country club in Palm Beach, a pump station was built, but they did not want their patrons to see it. MWI Pumps installed a 36-inch, 200 horsepower pump in a horizontal configuration that cannot be seen by country club members and guests. Electric submersible pumps offer choices for the kind of pumping station you want to install. “If you can think outside the box, you can install this kind of pump station however you want” Boudet said.
In Louisiana, MWI built a pump station in which angle submersible electric pumps costing $500,000 required building a $300,000 pumping station. Alternatively, a vertical installation would have cost $2.5 million because they must support the entire station in the canal or directly beside the canal. Sheet piling and other expensive structures are a must. MWI also uses angular contact bearings which can handle radial and down thrust in lieu of a vertical pump which can handle vertical down thrust.
4. Educating engineers on the losses in the system that are different than other pumps
When most engineers do a TDH calculation they are using the static head, friction losses in the pipe and velocity head or exit losses, Boudet explained. With a submersible electric you have a can that the pump slides down inside. With this configuration you have the pump/motor in the discharge flow (this cools the pump, which is an advantage), but you have a motor region loss that must be calculated. It is usually .7 of velocity head.
Boudet said that many engineers will use a spread sheet or standard formula they’ve used for many years for line shaft pumps. However even with this small additional loss taken into consideration, the local parts availability, ease of installation, and the lower cost, then the advantages are still there. They simply must understand the concept of motor region loss, he explained.
“Once an educated customer understands the efficient and effective solutions electric submersible pumps offer, submersible electric pumps often become an easy choice”.