Pumps for life

?There are many readily applied steps available to UK process companies when it comes to reducing the life-cycle costs of both new and existing pump systems - if they know how and where to start.

For AxFlow UK managing director Tony Peters, motor efficiency and maintenance should among the first considerations with any life-cycle assessment - simply because these factors account for such a huge portion of overall cost.

“It’s never too late to look at energy-efficient motors - just do the math on kW cost saving versus time of usage,” comments Peters. “Look at new variable speed drives as an alternative to inefficient throttling of pump flow with valves.

“Measuring bearing temperatures and vibration monitoring are easy ways to adopt a preventative maintenance regime. Be ahead of the game to prevent inconvenient pump failure.”

When it comes to investing in new pumps, the Axflow MD advises operators to look at the type of pump being used, and check to see if there are more efficient alternatives.
“Often centrifugal is the only pump type thought of, however rotary positive displacement and reciprocating pumps offer far greater operating efficiency albeit at a larger initial capital equipment investment.

Materials

Another recommendation is to investigate the materials of construction used throughout the pumps.

“Perhaps a more erosion/corrosion-resistant plastics pump might offer a much longer life than cast iron/stainless steel,” Peters suggests. “Most pump repairs involve seal failure, so why not look at seal-less pumps? - there are so many alternatives available nowadays, so get expert advice.”

Overall, though, Peters believes the most common pitfall is for users to trade ease-of-operation for long-term efficiency.

Very often, the pumps that are simple to ‘use and abuse’ are very inefficient, so end users need a balanced understanding of operating costs. Eliminate operator abuse in a pump/system operation and you can then re-evaluate the pump selection.

“Like any piece of equipment - if you treat it with care then you will get longer life. Any good craftsman would tell you ‘choose the right tool for the job - then look after it’. Why don’t process users apply this rule more often to pumps?,” asks Peters.

For his part, Charles Howden, engineered products manager, UK & Ireland at Mouvex, lists the main life-cycle-cost factors as application/control, motors and pump design.
New pumps are typically oversized and, therefore, operate inefficiently once installed. It is, therefore, worthwhile looking for inefficient control by checking installations for regulation using control valves, by-pass lines and to consider substituting variable speed drive systems.

When it comes to motors, Howden’s advice is to check the pump drive motors for efficiency and rewind history: “A rewound motor is never as efficient as a new one. Motors operate most efficiently at rated output. So check if there are options for down sizing.”

Looking at pump design, the Mouvex manager urges users to determine if the installed pump is the most “appropriate and sympathetic” to the process, system and handled product.

“System reliability and maintenance needs can be negatively affected where an applied pump has a pulsing characteristic and the process involved is pulse-sensitive,” said Howden. “In these situations, consider substitution with a pump type having a non-pulsing, volumetric characteristic.”

With many pump types, residual product cannot be stripped from lines once an operation is completed, so additional processes are required to clear lines between operations.
“Utilising a pump type capable of fully pressurising and stripping lines will recover valuable lost product and also avoid the need for additional line-clearing processes,” said the Mouvex expert.

On certain applications, pump types can suffer damage when run dry, be incapable of self-priming, suffer high seal maintenance costs and cause excessive shear damage to handled product.

Where some or all of these issues apply, Howden suggests substituting a low-shear pump design capable of handling dry operation and of self-prime, and utilising a simple seal-less design without magnetic drive system.

“Consider substituting centrifugal types with PD when handling viscous products, where variations in system pressure occur and where shear-sensitive liquids are involved,” he advised.

When it comes to investment, companies should to pay special attention to pump efficiency and maintenance costs because the initial capital purchase can represent less than 14% of a pump’s total life span.

Companies, said Howden, should also “determine an analysis period and factor in assumptions for inflation in energy, labour and material costs. Obtaining maintenance recommendations and MTBF (mean time between failures) data from the vendor as a basis for repair and downtime costs is also a good idea.”

For Howden, one of the biggest oversights among end users is not fully using a life-cycle cost strategy when purchasing new equipment. This includes giving too much consideration to initial purchase cost, which typically represents a maximum of 14% of the total life cycle cost.

“A well specified and energy-efficient pump may compare unfavourably initially, but will often repay its premium within one or two years, and thereafter produce net savings to the end of the life-cycle term,” he remarked.

Size matters

Another oversight occurs when end users design and specify pipe and valve systems for minimal size and initial cost.

“This is usually at the expense of larger pumps and reduces energy efficiency due to increased friction losses. Any initial cost gain is quickly lost and a negative impact on life-cycle costs remains to end of the term,” said Howden.

According to a Wanner International spokesman, the first consideration in choosing a process pump has to be fitness for purpose. It must be able to handle the fluid it is pumping, while meeting specific requirements, such as flow rate, pressure and temperature, and with due regard for safety. It must also, he emphasised, be reliable.

“If it is falling short in some way life-cycle costs will be unnecessarily high. This could be because the guidelines laid down by the pump manufacturer are not being observed, poor maintenance, inefficient control systems, and/or using the wrong type/size of pump for the application,” the spokesman said.

“Regardless of how good the technology is, poor installation, operation and maintenance could lead to failure or higher than necessary life-cycle costs,” he added.

All the main pump suppliers understand the capability and limits of their equipment, however, if these are not supported by the right level of applications engineering and service, this could result in unplanned, costly, downtime or operation, according to Dr. Don Collins, market development manager, chemical sector, at Edwards Ltd.

“Preventing failures is usually the single most cost-effective measure to take since downtime is often the most expensive item on a plant,” said Collins, who is responsible for Edwards’ global chemical dry pump applications engineering.

The Edwards expert lists simple cost-saving opportunities for mechanical vacuum systems as including the use of inverters for low power use when the system is not on process, replacing expensive chilled water with cheaper tower water, if feasible, and reducing or eliminating waste.

The best thing a company can do, he said, is calculate the cost of ownership of the existing vacuum system and compare this to replacing the system or improving the system with help from the supplier. This means accounting for the total installation cost, the running cost, the annualised maintenance cost and the cost of potential failure or the avoidance or elimination of failure.

“Reliability is usually the most important factor, yet it is seldom calculated explicitly. When it is, you should find that in most cases, it is the supplier that has the most expertise and reach who will prove to be the most cost-effective in the end,” concluded Collins.

“Many customers often concentrate on the capital cost of the equipment, neglecting even the rest of the installation cost, let alone the running cost. If capital cost is the only factor in the cost analysis, the selected system will almost certainly prove to be the most expensive over the life cycle of the process.”