And the Wanner is ... or is it?

Purchase price should be far from the only consideration when buying a new pump. Many in today's industrial environment might also consider installation and commissioning costs as well as energy and operating costs. But how many will think about the expense involved in maintenance and repair, downtime and loss of production, environmental factors and the final cost of decommissioning and disposal?

Initially, of course, it is as much about the motor as the pump, not forgetting the base plate and the cover, as well as an auxiliary device, for example, if you have double mechanical seals. Fluid and pressure have to be supplied to the pump, and this device could be more expensive than the pump. Installation and commissioning is likely to include both hardware and software costs. And will staff training be required?

If the pump is a complicated design then it could well have high energy and operating costs all the time. If it fails and you are pumping a high-price product then shutdown will be very expensive, possibly more expensive than the pump itself.

So, there are many factors to consider when buying pumps. One expert on such matters is Dr-Ing Friedrich-Wilhelm Hennecke, who worked at BASF for 30 years. He has been chairman of the pump working group of the German chemical industry and a member of the German pump standardisation committee.

Hennecke has devised a method and calculation for life cycle costs (LCC) but says this is only relevant when comparing different pump types, such as centrifugal and positive displacement, rather than comparing similar pumps from different manufacturers because, in this case, the cost differences are only minor.

At the request of Wanner Engineering, Hennecke carried out a life cycle cost comparison for five different types of pump. These were Wanner's HydraCell positive displacement pump and pumps of the centrifugal, side channel, peristaltic and membrane piston type. These latter types were supplied by prominent manufacturers and they were able to choose which pump they supplied to meet Hennecke's specification in terms of flow rate and head pressure. They also supplied prices for the pumps and their spare parts and how often parts needed to be changed.

The tube on a peristaltic pump needs to be changed after 1,000 hours, typically. Centrifugal and side channel pumps have a mean time to failure of three years, said the German expert, while the HydraCell will operate for 4,000 hours before key parts need to be changed.

The scope of the investigation covered flow rates of 1.4, 4.2 and 8.4 m3/h and pressures of 5, 10, 50, 75 and 100 bar.

At low pressure and low flow, the life cycle costs for the centrifugal, side channel and Hydracell pumps are almost the same. Peristaltic and membrane piston pump costs are higher because of their greater repair costs, although the investment price for the piston type is also significantly higher.

For high flow rates and at low pressure, centrifugal pumps are clearly the best, according to Hennecke. Investment costs for membrane piston types are high, although they have benefits in terms of energy bills.

Centrifugal, side channel and peristaltic pumps are not suitable for installations operating at high pressures and high flow rates. Life cycle costs for the HydraCell under these conditions are only half those for membrane piston pumps, although energy costs are similar.

In his final analysis, Hennecke said the HydraCell is the most economic pump across his evaluation range. Sidechannel pumps are rated similar in terms of LCC, but they can only handle clean fluids.

Centrifugal pumps are best confined to applications operating with high flow rates at low pressures. Peristaltic pumps put a high demand on replacement tubes.

In application terms, side channel, centrifugal and peristaltic pumps are limited to pressures below 10 bar. Above 10 bar, membrane piston pumps have a better efficiency than the HydraCell, but their initial investment and the cost of spare parts and labour needed to change membranes are said to be extremely high. Thus, above 10 bar, the LCC for a membrane piston type exceeds the HydraCell by a factor of three, according to Hennecke's calculations.

While accepting that the approach taken by Dr Hennecke is broadly fair in the report commissioned by Wanner, other pump makers point out that the results were significantly influenced by the applications used in the comparison.

In particular, Mike Sullivan, marketing manager at UK pumps maker Watson-Marlow Bredel, said the use of different type of fluids would have yielded some very different conclusions.

"The biggest problem is that it is an abstract comparison — clean fluid," commented Sullivan, whose Falmouth-based company is a leading manufacturer of peristaltic pumps.

Peristaltics are widely used to solve many pumping problems such as abrasives handling, fibrous materials, corrosives and gassing fluids, which are contained in the peristaltic hose, according to the Watson Marlow manager.

These materials wear ball valves and seats, clog valves and corrode components in other pumps, continued Sullivan, adding that when entrained gas builds up in a diaphragm pump it will stop pumping.

"Likewise centrifugal and side channel pumps would not be used in the same application areas. Dr Hennecke states that the side channel pump will only handle clean fluids ..... so it is not really a like-for-like comparison," he emphasised.

Sullivan further noted that while the peristaltic pump data "seems about right" it is based on a competitor's pumps and does not reflect the latest state-of-the-art technology in this field.

For example, Sullivan pointed to Watson-Marlow's hose grinding technology which, he said, can double hose life and therefore reduce the maintenance and overall life cycle costs of perstalic pumps.