Protecting dewatering and slurry pumps' seals is key, Steve Skinner reports.

By Steve Skinner06 May 2009

Tsurumi pumps has introduced a sacrificial shaft sleeve to keep solids away from the mechanical seal

Tsurumi pumps has introduced a sacrificial shaft sleeve to keep solids away from the mechanical seal on its pumps.

Slurry and dewatering pumps are perhaps the unsung heroes of the construction site. Steve Skinner reports on the technology being adopted and the challenges being faced by a sector in which reliability is key.

In terms of materials used and design, seal technology continues to advance across the sector. Paul Aguilar, service and operations manager for Mody Pumps told CE, "The seal is at the heart of the pump and a pump's longevity depends on it, so we are continually researching materials and systems in this area of the pump."

In June Mody will launch a new high chrome slurry pump with agitator that will be able to pump up to 60% solids. To achieve this the company has designed a system that encapsulates the mechanical seal in a cartridge that then sits in an oil bath.

The seal is made from silicon carbide to resist the silica in the slurry and Mody believes this unit will allow the pump to take more abuse than anything it's manufactured previously.

The new 50 kW version of the MSP series slurry pump (the range will top at 99 kW) will be capable of pumping 850m3/hour with a head of 88 m.

Beyond the MSP series, Mody continually evaluates its dewatering range too in order to see how that might also be improved.

Mody is credited with introducing centre line discharge on its pumps (developed for dropping into wells in the US) and more recently the company introduced its ‘double-damp' arrangement to prevent wicking (damp travelling into the pump motor via the electrical cabling) where the individual wires have grommets as well as the outer core of the cable.

Seal separation

Tsurumi Pumps is recognised for its robust sealing system, whereby both mechanical seals are protected not only through the use of quality materials but also by being physically separated from the pumped medium.

"We don't see any need to change because we consider our seal system to be very advanced already," said Stefan Hörnschemeyer, marketing manager at Tsurumi (Europe).

"We use a double mechanical seal inside the oil bath, which means that no part of the seal comes into contact with water. Through this system we reduce the requirement for expensive seal replacements," Mr Hörnschemeyer told CE.

Tsurumi has also introduced a sacrificial shaft sleeve, which is a simple metal ring, to act as a first line of defence. "It's a cheap component, yet it's effective at keeping sand away from the mechanical seal," said Mr Hörnschemeyer.

The new GA200 light duty submersible pump from Pumpex features a triple shaft seal and dry, air filled motor for improved efficiency. As well as auto level control, built-in non-return valve and quick connection easy clean strainer, the GA200 also comes as standard with the company's 'dry suction adapter'.

ABS is equally confident of its seal system. "We use silicon carbide for our primary seals because its wear resistant, shock resistant to temperature fluctuations and performs well in the lubrication aspects of the pump," said Jonas Bladh of ABS Group.

"We don't see any major developments away from this in our primary or secondary seals."

ABS recently introduced what it terms its ‘service factor', which means there's a +/- 10% thermal tolerance built into the pumps. This means the pump automatically trips out when it runs dry and then automatically re-starts once water returns.

Graeme Saunders, sales manager at Godwin Pumps attributes their success to the use of cast chromium steel hardened to 200 HB for the construction of its impellers as well as the adoption of oil bathed mechanical seals.

"The cast chromium steel gives our impellers excellent wear characteristics," Mr Saunders told CE. "Additionally, we equip our pumps with renewable front and rear wearplates that can be shimmed if required.

"Our CD range of Dri-Prime pumps lend themsleves to both slurry and dewatering applications and with up to a 90 m head and solids handling capability of up to 75 mm, we're offering a reliable, cost-effective solution," said Mr Saunders.

ITT Water and Wastewater also credits the efficiency of its NV diesel driven pumps to a new hard iron impeller design, which it says lowers operating costs. The Swedish company's NV range spans connection sizes from 100 mm to 300 mm and ITT expects to launch the series with a 15 cm model in the last quarter of this year.

With a head of 49 m the 15 cm model will feature of flow of approximately 300 m3/hour.

Application

Be it dewatering or slurry pumping, the key is to adopt the correct system for any given application.

"Individual pumps are designed for particular applications and to minimise wear it is important to understand each application," Mr Bladh told CE. "It is important to fit pumps to application."

Mr Aguilar of Mody told CE, "Damage comes from misapplication and users need to understand the needs of the application before ever putting a pump on site."

In Sweden, Grindex is running training seminars for its customer's service technicians as well as offering help with the selection of the right pump for each given application. "A Grindex pump is an investment that will serve a customer longer if it's used, treated and serviced correctly," said Kent Bostrom, marketing communications manager.

"A key issue is how to reduce wear and Grindex pumps are manufactured with a range of features to keep abrasive particles away from the seals."

Market

Increasing pump efficiency will seal market share in the future according to Mr Saunders at Godwin Pumps. "As we continue to push globally for ‘greener' equipment that does not sacrifice performance, pump companies will need to work to increase efficiencies," Mr Saunders told CE.

Tsurumi meanwhile determines that lifetime cost is the most significant driving force. "We don't consider either productivity or efficiency to be the key drivers, because our emphasis is on machine durability," said Mr Hörnschemeyer.

"We are looking at productivity measured in terms of overall lifetime cost rather than basic price and performance," Mr Hörnschemeyer told CE. "Long term usage and easy maintenance are important where pumps, in comparison to the whole construction site, represent a very small share of the equipment investment."

PX Pumper of Denmark last year moved into new production facilities that will enable it to improve production flow. "The new facility is twice the size of our previous building and offers us exciting opportunities," said Tom Schultz, managing director.

"At PX Pumper we adhere to a philosophy that says nothing is too big or too little. We can match the large producers and fulfill huge orders but we can also create pumps that fit the specific needs of every small client," Mr Schultz told CE.

Challenges

The greatest challenge facing pump manufacturers is that of unit strength. "The dewatering market particularly is of a portable nature so pumps need to be robust in order to cope with handling," Mr Aguilar told CE.

A point not lost on Mr Bladh of ABS who said, "We know that our equipment is moved around from site to site and used across a range of different jobs. In this respect, it's important that our pumps are robust."

Strength, durability and flexibility will drive pump design over the next year and as more advanced pump seals and impellers are developed external appearances will continue to deceive.

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