Analyzing failing large stormwater pumps
When you see the early signs of a stormwater pump reaching the end of its life or when it becomes obvious that the efficiency is dwindling, it’s important to look at the options and make the best decision for the application.
According to MWI Pumps expert Marc Boudet, there are three options when your stormwater pump begins to fail:
Repair the pump
Obviously, this is often the first inclination. Invest a few dollars to replace the bearings, seals, and apply a new coat of paint. However, Boudet cautions against making such a quick decision. “Are you saving money or putting lipstick on a pig?” he said. “Sure, in the first 15-20 years this may be ok, but as the pump ages, wears, and corrodes, other items need to be addressed—like the shafts and propellers to name a few.”
Replace with the same type and size pump
This seems to be a sensible solution, but certain questions and concerns still exist. There may be no change to the structure, and the new pump may produce the same amount, but ask yourself, does the driver need to be replaced? Is the engine or motor producing the same power it did when it was new? Did you replace the discharge pipe? Is the roughness factor adding head that you didn’t have before? Is the efficiency the same or are there other options available now that maybe were not available 30 years ago? All of these questions must be evaluated in this decision.
Retrofit with a different style of pump
Sometimes, experts have an opportunity to recommend a new technology for an old application. Maybe this technology wasn’t around or maybe the end users or engineer just weren’t aware of the option at the time the pump station was originally built.
When you pull the pump out of operation to perform the analysis, an experienced engineer or service operator can use his senses to make some critical decisions, Boudet said. “You can just listen and know whether it needs new bearings. You can see if it needs new seals. You can learn some things just through listening, paying attention, and relying on your own experience.”
With these options in mind, first ask a few key questions to help determine whether repairing, replacing, or retrofitting is the best option.
Is there a different type of equipment that may work that may also save us some money?
Boudet recalls an example from a pump station in Louisiana in which 54” horizontal pumps were installed in the 1950s. There was a line on the suction side and another on the discharge side. Both lines were submerged. A vacuum pump would evacuate the air, pull the water up to the propeller and then the pump would start, creating a siphon.
This is good in theory, unless one side is out of the water. There was not enough horsepower to pump without the vacuum pulling water from both sides. Boudet said that hydraulic pumps did not exist until the late 1960s, so retrofitting an upgraded technology into an application like this one sometimes makes a lot of sense.
Are the materials worn out?
“When you get the pump into the shop and realize, for example, that the steel that should be a 1/4” thick is now 1/16” thick, well, you may not be able to make the repairs needed to put this pump back into operation,” he said. “When you sandblast it, does it blow holes right through it? It’s a good idea to think in terms of determining if it followed the ‘80 percenter’ rule. This means that if it is 80 percent of the cost of a new pump to repair it, and all you would really keep is the baseplate and the elbow and everything below it like the column, bowl section, intake valve — and everything else would need to be replaced — well, maybe it’s time for a new pump.”
Is this the right pump for this application?
Some people will install the wrong pump for the application strictly because that’s what they’ve always known. They may not shop around for a more efficient pump option, or maybe a technology that didn’t exist when they originally installed this one may be a better solution for this particular application.
How have the events and circumstances of the site changed?
Considering whether to upgrade or not could mean installing a better pump that is more powerful or more efficient for the application. However, what happens if the circumstances change over the course of the pump’s life? You might find for example, when the pump station was installed only 20,000 gpm was needed because it was not a fully-developed neighborhood. Many years later there may be a lot of runoff due to development. Perhaps there is more concrete and more asphalt and now that same location might require double the flow than it once did.
“This is one of the beauties of hydraulic pumps,” Boudet said. “We can install a pump with 200 horsepower to maybe only pump 15,000 gpm. We install hydraulics that handle this but with a cam change, we can up the hydraulic oil flow to pump more gallons per minute. As long as the original horsepower can meet the higher flow condition, this is no problem. Looking at things this way and thinking outside the box can provide some interesting and creative options.”
Is it more expensive to repair it than to replace it?
Boudet said this is a critical question. “If you have a pump that’s 30 years old, and it will cost you $15,000 to repair it, ask yourself if it’s really worth it to put $15,000 into something that is only worth $10,000? In some cases, it’s a better idea to spend $50-60,000 to replace it.”
There are many customers in certain industries who may continuously make repairs because they want to go the cheapest possible route, Boudet explained. “However, a municipality will generally look at a $100,000 pump and think about how it’s a bad idea to spend $80,000 to fix it. A stormwater pump may last 30-40 years, so perhaps this is a good time to just replace it.”
When is it time to replace your stormwater pump?
It really comes down to cost, Boudet said. It’s not simply when it doesn’t run, but when it’s no longer cost effective to operate it.
Is a rental pump an option if you can’t afford to repair, replace or retrofit the pump?
MWI Pumps can provide rental pumps that the customer can utilize while their pump is being repaired, or while they are considering options to replace it. However, this is only a temporary option for a permanent stormwater pump station, Boudet said. “It’s not a great idea to remove one used pump and replace it with another used pump as a permanent solution. However, MWI has the capability to provide new pumps and offer the customer rentals at a reduced price to do the job temporarily while their new pumps are being manufactured.”
There are many considerations when making a final decision on whether to repair, replace, or retrofit a failing stormwater pump. MWI Pumps has a team of experienced, dedicated, in-house sales engineers to help with these decisions. To save time and money, reach out for a FREE consultation and recommendations on viable options for your application – Discuss your needs with our engineers today at 954-426-1500, [email protected] or visit Custom Engineering for more details.
There is no magic bullet for everyone, Boudet said.
“Replacing is not always the best option, but sometimes it is,” he said. “A new pump doesn’t mean it’s the best choice for the application. The original pump may not be doing the job appropriately.”