So, the pump is a little long in the tooth; it still functions but performance and efficiency have dipped to levels that are impacting operations and energy bills. Many plant engineers in this situation will have found themselves pondering the repair-or-replace dilemma.
Before determining the optimum way forward it is worth identifying why pump performance and efficiency diminish over time. According to Paul Pearce, sales director at industry service provider Rotamec Engineering Solutions, there are many factors at play here. He says: “Key influencers that affect pump performance include: surface roughness; internal clearances; mechanical losses such as bearing wear and failure; lip seal deterioration; mechanical seal deterioration; cavitation and impeller wear; and changes in the media being pumped.”
In the event that one or several of these circumstances begin to affect pump performance there will likely be a number of visual indicators, such as increased power consumption, reduced pressure or more frequent blockages. Further tell-tale signs can include increased vibration, higher operational noise levels, reduced production output, or the pump deviating from its performance curve.
“The interval period for pump maintenance varies from application to application, but is typically determined by factors such as the media being pumped, the environment and the customer’s budget. To provide an example, we would recommend a service every six months for a sewage/wastewater pumping station, and generally an annual service/inspection on other pumped liquids,” explains Pearce.
For those thinking that a maintenance check comprises little more than a basic once-over, think again. At Rotamec, the company has a 19-point checklist of all pump components. Such checks include those for sump condition, motor resistance, cable condition and security, oil, impeller condition, vibration and noise, guide rail fixings, running amps, valves, earth bonding, and lifting chains.
“A standard pump repair at Rotamec would begin with a complete strip down and the identification of worn parts,” says Pearce. “A quotation is then provided for the required repair, including photographic evidence. Once approval is received, the repair is undertaken, with the pump re-assembled, tested, resprayed and despatched or reinstalled on site.”
Of course, there are situations when a repair, no matter how effective, is not the way forward. For Rotamec, there are clear circumstances when this eventuality comes to bear.
“We would generally recommend pump replacement rather than repair and overhaul when the unit is either aged and parts are obsolete, when the power consumption on site dictates a pump upgrade, or when the repair/overhaul costs are more than 70% of a new replacement unit,” says Pearce. “However, as a matter of course, we always provide customers with a repair price [where possible] and a new unit price.”
Another specialist in this area, Dura Pump, has produced a six-point guide that covers the main factors to consider when contemplating pump repair or replacement. The first is pump age and type. If there is life left in the pump and a certain level of lower efficiency can be tolerated, a repair will be more cost-effective. On the flip side, most new pumps are greener and more energy-efficient, so a replacement could save more money over time, particularly if there is a risk that the repaired pump might fail again.
Further considerations, according to Dura Pump, include the actual run time of the pump, the number of repairs already performed and the regularity of failures. Space is a further point of scrutiny: would a new pump fit the space vacated by the previous pump?
The company also cites lead times, disruption and downtime as additional influencers. Not all pumps are available from stock; can a new one be obtained within a reasonable lead time? A delay could prove costly, meaning an interim repair may be the only option. In addition, what about the plant context? Is it a critical pump with no back-up? If so, a repair might prove less immediately disruptive than a replacement.
Dura Pump says there is “no right or wrong answer to whether to repair or replace. There is a careful weighing up of factors after intelligent analysis.”
In a recent case study example, a large UK distribution warehouse needed critical support during the COVID-19 lockdown to maintain supermarket supplies after the sudden deterioration of drainage pumps due to increased demand. A service visit by Dura Pump revealed that some pumps were producing a reduced flow rate. Despite many issues – such as signs of bearing failure, rotting guide rails, a pit that was full of debris and gravel, blocked NRVs (non-return valves), and worn impellers – repair was deemed the optimal route, particularly due to the urgency of keeping the warehouse operating to capacity.
Dura Pump’s engineers completed numerous tasks, including dismantling and cleaning the NRVs, and unblocking and replacing the balls, which were heavily worn. The guide rails and guide rail brackets were also removed and replaced with stainless steel variants. Another pump received new bearings, a mechanical seal, O-rings and a new impeller. In addition, to making the repairs, Dura Pump also recommended drain-tracing the system and a full drainage survey to discover where gravel and debris were entering.
According to ERIKS Pump Services, its data logging and condition monitoring can reveal key information that includes pump performance and energy efficiency. With these facts and figures to hand, the company can work with customers to determine whether they should continue to support existing pumps or carry out replacements.
If maintenance or repair proves more cost-effective, the reverse engineering capabilities of ERIKS Pump Services mean it can help keep pumps running even after component obsolescence, and modify and up-rate components for improved performance and reliability. This process can include a material upgrade, with the ability to engineer-out any wear or damage to the original parts. General pump types supported include both rotodynamic and positive displacement.
In 2016, the European Commission published its ‘Putting Energy Efficiency First’ study, which suggested that energy bills can be as much as 20% higher due to inefficient pumps, according to service provider Pumping Solutions. With this thought in mind, the decision to repair or replace should be taken sooner rather than later.
BOX: MORE EFFICIENT CENTRIFUGAL PUMPS
Houghton International has been appointed as a channel partner of oil services company Baker Hughes, focusing primarily on API 610/ISO 13709-compliant centrifugal pumps in the UK and Ireland for petrochemical applications. The agreement allows Houghton to provide overhauls, repairs, parts and replacements.
Some of the more than 150 units have been operating for 30-40 years, so Baker Hughes’ knowledge and technology sharing with Houghton International is claimed to be able to help improve pump efficiency, reduce energy consumption and extend mean time between failure (MTBF). As an authorised channel partner, Houghton will also be able to support the specification and installation of new Baker Hughes pumps across various sectors.