Solving 7 common issues in above ground and submersible pump systems

Learn how common issues in above ground and submersible pump systems can be solved by Grundfos solutions, using a real-life case study of a mining company sourcing water from a distant lake.

In this video, we will examine a case study involving a mining company that faced the challenge of sourcing its daily water supply from a lake situated 10km away from its facilities.

The original engineering designers proposed a classic solution, suggesting the use of above-ground, end-suction type and vertical multi-stage centrifugal pumps, which would need to be installed in a newly constructed pumping station building.

Grundfos provided support through consultancy and evaluation of the installation, which concluded that using above-ground pumps would result in a suction lift issue.

As a result, 6 key challenges emerged, primarily concerning the intake of water from the lake. There was a potential seventh challenge that could have arisen based on the conditions of the lake. While this challenge never materialised, Grundfos had prepared a solution just in case. We will explore this potential challenge as it is likely to occur in similar situations.

The challenges included:
• The inability to meet the Net Positive Suction Head Required (NPSHR)
• Aggressive water
• Pump motor overheating
• Minimum submergence – the potential challenge Grundfos faced
• Pump clogging caused by debris
• The ability to lift the pump in and out of the water
• Concerns about water hammering and high pressure in the original pipeline

Let’s begin by exploring the first challenge: The inability to meet the NPSHR.

The Grundfos above-ground pumps, were initially chosen because they fulfilled the hydraulics requirement of the application.

They seemed perfect for the application until Grundfos evaluated the site. Due to their limited lifting capabilities, the pumps wouldn’t be able to lift the water out of the lake, making them unusable.

The above-ground pumps also caused other cost-related problems for the mining company, which included:

The construction of a new building .... to house the pumping stations ... along with the use of plumbing and electrical systems.

Grundfos were brought in as design consultants to ensure the perfect solution for the application.

After recognising the main challenge of lifting water out of the lake, our solution experts suggested installing a large stainless steel submersible pump (or SP) as close to the lake floor as possible. Placing the pump within the lake meant the challenge of lifting the water would be removed. Not only was the water efficiently moved from the lake, the customer saved time and money by avoiding construction and obtaining approvals from local authorities.

Presence of aggressive water:
The second challenge that emerged was the aggressive nature of the water in the lake, which would cause corrosion and damage to the submersible pump over time and cause additional problems, including:
• Maintenance issues – The corrosion would require frequent repairs or even replacement of the pump, and
• Cost issues – The constant need for repairing or replacing pump parts, or the entire pump itself, would cost the customer a lot of money.
To remedy this, Grundfos recommended the SP 215-6-AAR pump with 110 kW MMS 8000R motors.

This pump was specifically designed with special stainless-steel materials to withstand the corrosive water in the lake. With this solution, concerns about corrosion were eliminated, and both maintenance and cost issues were significantly reduced.

Pump motor overheating:
As the pump was to be placed in an open body of water, a specific water flow was required to keep the motor cooled. If the motor had not received efficient cooling, it could have resulted in diminished pump performance, motor damage, or even a system shutdown.

To address this requirement, Grundfos installed a flow sleeve that provided efficient motor cooling and extended motor life. The sleeve allowed the water flow to enter from the motor’s end, ensuring it passed over the motor before entering the suction. It had a small space between itself and the pump, which increased water velocity between the internal diameter of the flow sleeve and the outside diameter of the motor. This increased velocity prevented debris from building up on the motor or the sleeve.

A basket strainer was also included on the bottom of the flow sleeve to keep any debris from entering the pump. Both the strainer and sleeve were made using the same material as the pump to prevent any damage and corrosion caused by the aggressive water.

Minimum submergence:
Due to lake water levels varying throughout the year, the submersible pump could’ve potentially faced a challenge regarding minimum submergence. If the water level in the lake dropped too low, air could be pulled into the pump. If this happened, the pump could suffer severe damage.

This was an issue Grundfos had to consider during this case. While it was determined that minimum submergence wouldn’t be an issue, Grundfos had a solution prepared just in case. The solution was to install a vortex suppressor.

This device would have changed the submergence characteristics by redirecting the water flow around the plate, creating the illusion that the pump was deeper in the water than it was. This would have protected the pump from potential damage as air would’ve been prevented from entering.

Pump clogging caused by debris:

Despite the addition of a basket strainer to prevent debris, there remained a high risk of clogging in the pump as it would be placed at the bottom of the lake in the mud. To overcome this challenge, Grundfos designed and attached a skid at the bottom of the submersible pump. The skid holds the pump off the lake floor, preventing debris build-up.

The ability to lift the pump in and out of the water:
All of Grundfos’ solutions were developed to ensure long-lasting and efficient performance, but there would eventually be a need for the pump to be serviced. A submersible pump positioned at the bottom of a lake would be difficult to lift in and out of the water. The skid that Grundfos designed also helped solve this problem. Lifting eyes were attached to the top of the skid, allowing for easy installation and removal whenever necessary.

Concerns about water hammering and high pressure in the original pipeline:
The final challenge was a high risk of water hammering and high pressure in the original pipeline. Sections of the original pipeline were unable to handle the large amounts of water that needed to be moved, which could lead to pipe explosions. To address this issue, Grundfos proposed the use of the Grundfos CUE Variable Frequency Drive (VFD) with the submersible pump. The VFD allowed for adjustments in...
pipe fill
soft start
and ramp-up speeds to reduce the risk of water hammering.

To meet the required conditions of maintaining a constant flow rate of 250m3/h with a head of 104 meters, Grundfos installed a pressure regulator. The regulator helped relieve excessive high pressure and compensate for the 10km distance to the facilities.

Throughout the project, the customer trusted Grundfos’ expertise and benefitted from the deep application experience and solution consultancy we provided. Grundfos' ability to identify an application issue related to the suction lift early on saved the company from making a common but costly application mistake.

This would have required obtaining approvals from local authorities and would’ve resulted in months added to the construction timeline, delaying the start-up of operations.

This saved the customer operating expenses and capital expenditures as well as ensured uninterrupted water supply for their production needs. Since the installation in 2015, Grundos' solution has operated successfully.

The customer rewinds the motor once every 5 years as a proactive approach to prevent failure and costly downtime.

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