Innovative design, engineering and high-performance testing highlight the KSB pumping system to be installed 85 meters beneath the River Thames.
by Pumps & Systems Staff

The first four pumps are expected to be installed in the third quarter of 2015. After one year of operation, KSB will disassemble and fully-inspect one of the pumps. The pumps will be maintained and serviced by the specialists from the Britain-based KSB Limited.

“These Super Pumps have been challenged a great deal during this project, and so have we,” Ulmschneider said. “Seeing these pumps being pushed to the edge and not fail gives us a lot of confidence for all the challenges to come. We are ready.”

Powering the Super Pumps

Pumping power of this magnitude requires a motor that is customized to handle extremely high temperatures and voltage. Each KSB Super Pump is powered by a Siemens A-modyn vertical motor, which runs at 3.4 MW at 6,600 volts/50 hertz and speeds up to 333 rpm.

“Our challenge was to design a motor that could increase the power factor to 400 amps,” said Torsten Fiedler, Siemen’s sales manager for medium-voltage motors. “We added iron into the design to improve the power factor and the electronic behavior of the motor. This motor has a special electronic package. The stator of the motor consists of iron laminations. The more laminations in the design, the better the power factor and the lower the current.”

Each motor weighs 30.13 tons and measures 2.85 meters long, 2.75 meters high and 3.83 meters wide. The motor features a Rockwell Automation variable frequency drive.

One of the biggest challenges in creating the right motor to power the Super Pumps was the weight of the motor, Fiedler said. “Our competitor offered a motor that weighed 50 tons, but it was rejected by the client. Siemens was able to create a motor with the same power but with a lower weight.”

The Siemens design features a water-cooled motor. The motor has a constant air stream cooling circuit. The heat exchanger serves as the water cooler. Fresh water runs in between the motor casing and the cooling jacket. Water circulates and cools the inner parts. It is cooled by the rising pipe connected to the heat exchanger in the closed circuit. “This is a special design,” Fiedler said. “Usually, the water comes from an open source.”

These motors—manufactured at the Siemens Drasov, Czech Republic, facility—are a special design made for pump applications.

Mechanical Seal Technology

The mechanical seal is complicated and was specially made for this pump by EagleBurgmann design engineers Hans Steigenberger and Peter Haselbacher.

The Lee River HGH 300S1/400-E1 seals have split seal faces, which can be replaced without tearing down the pump (see Image 6). The shaft underseal is 279 mm (11 inches) in diameter. The seal weighs 300 kilograms.

Mechanical Seal Technology (continued)

EagleBurgmann and GIW worked together early in the project to carefully design the mechanical seal to meet the needs of the pump and also to account for the special challenges of the deep tunnel project.

“The seal for this project was specifically designed for purpose,” Haselbacher explained. “On the one hand, it is a simple semi-split case design—only it is much bigger. However, there are special issues with a vertical system. It must be straightforward and as safe as possible but engineered to purpose.”

In the HGH semi-split seal design, repairs can be made with the split parts. This is critical for this particular application, Haselbacher said. “Semi-split mechanical seals are used if there is sufficient axial clearance to pull off the seal housing and seat housing until the sliding parts are accessible. That is, only the wearing parts—such as the seal faces and O-rings—are split,” Haselbacher explained.

The Lee River HGH 300S1/400E1 sealImage 6. The Lee River HGH 300S1/400E1 seal

“In the case of the GIW seal housing, Part 4 is made split, for the case of repair, as space is limited. The seal faces, O-rings and springs can be replaced without complete disassembly. In the case of the GIW pump, the inflatable seal has to be activated.”

Haselbacher explained that the mechanical seal for this project was designed with an inflatable seal that blows up “like a tire” 2 to 3 bars above product pressure to prevent leakage. This is a safety precaution. The pump cannot run with the seal inflated. “The flowback device is state-of-the-art,” Haselbacher said. “This helps keep the seal chamber free of particles.”

The seal usually has a flush in with clean water (plugged Bore 1 in Figure 1) with about 15 to 20 liters per minute. This is to keep the area around the seal as clean as possible since a bell-shaped seal chamber cannot be used in this application, Haselbacher said.

“In case of necessary repair by opening ‘the flush out’ for cleaning (Bore 2) so the service personnel can clean up the seal chamber before opening. We flush the seal chamber with clean water.”

The plugged bore (Bore 3 in Figure 1) is for venting.