Pump maintenance: Better by design
1 Sep 2011
Maintain-in-place pump designs can help ease the pressure on plant operators, reports Patrick Raleigh
Although centrifugal pumps have traditionally been a familiar part of the internal workings of wastewater treatment transfers, progressive cavity (PC) pumps are often used for handling more viscous media such as filter cake and primary, secondary and dewatered sludges.
PC pumps incorporate a hardened steel rotor and resilient stator, which form discrete cavities within the pump. It is this unique design that enables them to transfer difficult-to-handle media, even types that appear non-flowing. They can also pull suction and vacuum without the need for constant priming, and so can be used above vessels and sumps.
These pumps have been designed so that flow volume is effectively linear to running speed, which means they are easy to adjust to required changes in flow demands. Unlike centrifugal pumps, PC pumps are not greatly affected by pressure, though can still suffer from ragging and grinders.
With the AMP 5 spending set on improving the lifetime cost-effectiveness of wastewater processes, treatment works are increasingly specifying PC pumps offering maintain-in-place (MIP) features to reduce maintenance and downtime costs.
Since the launch of its EZstrip pumps in 2009, NOV Mono claims that all UK wastewater PLCs have purchased the maintain-in-place design in various volumes.
These units have been designed to ensure that flow volume is effectively linear to running speed
“A number of UK wastewater PLCs have specified [the pump] as their preferred asset of choice,” said Mark Viner, European sales manager. “The increasing cost of maintenance and the drive to reduce downtime even further has accelerated [uptake] within the market.”
“One of our greatest challenges was to help our customers justify the replacement of non-Mono and other technologies, since the benefits extended way beyond PC pumps. In support of this, we have provided design assistance to enable [the pump] to be retro-fitted into almost any PD application.”
MIP pumps can reduce the time needed to replace a rotor, stator, coupling rod and joint by up to 95%, said Simon Lambert, group sales and marketing director at NOV Mono. The average time, he noted, to strip down and replace the drive train elements is usually one full day on typical sludge pumps; compared to just 30 minutes with an MIP pump.
Removing blockages
“For example, when the suction chamber is blocked, especially with fibrous material wrapped around the rotating shaft, the material has to be removed,” said Lambert. “Blockage of the inlet can rapidly cause damage to the rotor, stator and drive train, so it must be caught in time.
requently, the problem is only noticed when the flow stops and the protective electrical relays are tripped out; this signifies major downtime.
These designs are claimed to reduce the time needed to replace a rotor, stator, coupling rod and joint by as much as 95
“The chamber of the MIP pump has a two-piece design, which can be dismantled and assembled in place without requiring years of expertise.
It can be opened up and rebuilt with a spanner and an Allen key in a fraction of the time previously required. The coupling rod can be accessed in less than one minute, the suction chamber and rotating parts de-ragged and the chamber re-assembled in minutes.”
For a full MIP procedure, Lambert said all rotating parts can be removed and replaced in under three-and-a-half minutes, allowing the pump to be completely maintained in situ. The drive train can also be dispatched as an assembled unit, so on-site assembly by a skilled engineer is not required. The suction and discharge pipework can be left connected, minimising any pressure testing requirements and reducing the danger of possible leakage. There is also no need to disrupt electrical connections and access to the whole pump is easy and safe.
Weir Minerals -
Slurry pump advance
Sibelco and Rio Tinto are among the early adopters of a new centrifugal slurry pump from Weir Minerals, the companies using the Warman WBH design in Australia’s Tallawang and Mount Thorley Warkworth mining sites, respectively.
The WBH pump features a single-piece frame that is said to allow for truer alignment of the bearings, seals and impeller with the front liner while lowering the part count.
In addition, the pump’s ’One Point’ front liner adjustment mechanism gives operators the ability to both rotate and to axially adjust the liner relative to the impeller, even while the pump is running.
The ability to continuously minimise the gap between the liner and impeller can reduce wear of these components and ensure a superior, longer-term performance, while at the same time reducing production interruptions.
The design features built into the WBH slurry pump are meant to maintain top performance, according to Fred Bradner, Weir Minerals director of technology.
“Specifically, maintenance must be easy and predictable and the new WBH pump is built to ensure longer maintenance-free intervals, and a broader efficiency curve than other pumps in this class. That helps to increase production and reduces energy consumption, which contributes to cost savings,” Bradner said.
The WBH is designed to minimise the risk of catastrophic failure, with safety features including standard leak detection, optional vibration, temperature and wear monitoring, and the ability to add pressure relief and thermal cut-out devices.
“The pump ran beautifully from day one with no dramas whatsoever,” said Matt Cosgrove, maintenance supervisor at the Sibelco Australia Tallawang mine site.
“It’s definitely the pump of the future,” added Paul Burgess, reliability engineer at Rio Tinto’s Coal & Allied operation at Mount Thorley Warkworth mine.
Industry hazard -
Counterfeit danger
Billingham, UK-based Tomlinson Hall & Co, UK distributor for Richter Chemie-Technik, a German manufacturer of polymer-lined magnetic drive and mechanical seal pumps, shut-off, control and safety valves, has reported “a disturbing trend in the supply of counterfeit consumables within certain models of Richter Pumps”.
With the majority of pump applications for Richter pumps being for handling difficult, corrosive or hazardous fluids, often within hazardous locations, pump failure can not only prove expensive with process shutdowns, but also endanger process industry personnel.
“As Richter’s new UK distributor, we ran a competition to win a new iPad once users had registered,” explains Colin Simpson, sales director at Tomlinson Hall.
“On contacting these clients we then came across examples of where the engineers, while thinking their pump had genuine Richter consumables such as impellers etc, encountered a pump failure which had revealed the part was non-genuine,” said Simpson.
“Fortunately, we were able to supply genuine Richter parts on both occasions to our customers’ complete satisfaction and their pumps are now running perfectly again,” he said.
Simpson points out that the use of counterfeit parts not only negates the warranty but also results in non-conformity with the Directive on Machinery and, where relevant, the ATEX Directive. It can also impact on the performance of the original product or on the operational safety, for example, lack of dry-run capability, less efficiency or flow and head.
“The existence of these non-certified consumables within some of the pumps has created a situation whereby plant engineers, unaware of the counterfeit parts, could be putting their operations and staff at risk by thinking they were running genuine Richter pumps and consumables,” concluded Simpson.
