Many companies in the water and wastewater industries use high-flow, high-pressure peristaltic pumps at some point in their treatment processes. Consequently, there is no shortage of replacement hoses available from manufacturers out to make a fast buck by exploiting the financial pressures under which their customers operate.

However, while it is easy to understand why low-cost offers are so attractive, the plain fact is that non-standard replacement hoses are a false economy.

Considerable additional expense can be incurred through the use of less robust alternatives; they need more frequent replacement, not to mention the significant knock-on costs caused by loss of performance and associated failures at other points in the system, leading to expensive downtime.

These additional side effects often amplify the increased frequency of hose replacement costs by a factor of four or more. All this can far outweigh and negate the original savings made by low-cost purchases. In the light of hard facts and figures, it is difficult to understand how using non-standard parts can ever be viewed as a good business decision. Yet it continues to cause problems in the industry.

Lower efficiency levels, higher power requirements, greater wear, increased maintenance and greater risks of part/equipment failure – all these factors are overlooked in the face of significant savings.

Looking at just a handful of examples from the Watson-Marlow Bredel catalogue of ‘pirate hose horror stories’ gives some indication of the scale of the problems:

l At one installation where the operator had opted for the cheaper alternative, pumps were required to run faster and for longer periods, with a serious adverse effect on running costs and the overall efficiency of the sludge-handling system.

l At a multi-pump site, where undetected bearing failure resulted in shafts falling into pump housings, the cost of replacement rotors, pressing shoes, shafts, bearings, front covers and bearing seals was between £3,000 and £4,000 per pump. Spread across several pumps, this dwarfed any theoretical savings achieved by using pirate hoses.

l On another site using Watson-Marlow Bredel SPX100 (100mm bore) pumps, the result of using inferior hoses was two cracked pump housings, with replacement costs (excluding labour) amounting to £5,500.

In particular, bearing failures due to uneven loading or overloading, and stemming directly from variations in hose wall thickness, can have serious consequences in terms of operating costs and downtime, especially on unmanned multi-pump installations, where failure may be undetected or detected too late to prevent serious damage.

Premature failure

So what are the defects which potential purchasers need to consider before opting for the cheaper alternative?

As the only component in contact with the pumped media, the hose (or tube in the lower pressure designs) is the heart of any peristaltic pump. Dedicated hoses such as those produced by Watson-Marlow Bredel are essentially the end product of continuous research and development. Watson-Marlow Bredel’s hoses consist of a thick, resilient inner layer and an outer layer of natural rubber reinforced internally with braided nylon. They are produced to close dimensional tolerances – between 0.25mm on larger hose bore sizes and 0.4mm on smaller sizes – and ground to the precise diameter. Wall thickness is the key factor in the hose construction – a hose could be 2mm larger on the diameter, but if the wall thickness remains the same, the unsuspecting purchaser would not notice problems.

Recent measurements of a cheaper ‘pirate’ hose found the bore-to-wall ratio to be out of concentricity by 1.5mm each side – on a compressed hose up to 3mm difference, for instance. The resulting changes in compression forces lead to premature bearing failure and even broken pump castings. On a SPX100 hose pump, for example, the approximate 8,000N of load from this degree of over-occlusion would reduce bearing life by more than 50%.

Figures for hose life also highlight the wisdom equally of using dedicated manufacturers’ hoses, notably in the area of sewage sludge pumping and similar arduous waste-handling applications. One example of this is at a site where two identical pumps are installed for the same duty. A maintenance contractor replaced the original Bredel hose with a cheaper ‘pirate’ alternative on one of the pumps. 12 months later, the original Watson-Marlow Bredel hose is still in service. The second pump, using the pirate, is on its fourth hose fitting.

In another comparable sludge-pumping installation, pirate hoses last about 200 hours, equivalent to about one month’s service – a retrofitted Bredel hose is still in service after more than eight months.

Hoses that appear identical on visual inspection will not necessarily be comparable in performance. This is reflected both in hose life and the speed with which a hose change can be carried out. In one case, a maintenance contractor who customarily fits cheaper non-standard hoses normally took a whole working day to carry out a hose change on a Bredel SPX80 peristaltic pump. Our own engineers took under one hour to fit a dedicated 80mm Bredel hose.

There have been instances of dimensionally inaccurate hoses becoming stuck half in and half out of the pump housing, eventually having to be cut into pieces before extraction of the offending item was possible.

Significant savings

It is also important to take into account lack of provenance, non-compliance with standards, the reputation of often little-known manufacturers and products with no real validation that the parts being purchased will perform at the required levels.

Add in the complications of compromising original manufacturers’ warranties (plus insurance implications), and those significant savings all too quickly start to unravel.

The truth is that only highly engineered, high-performance, precisely fitting parts will provide the accurate flow rates, long-life and 24-hour reliability required by water and wastewater treatment providers. This is key to achieving low whole-life costs, and the very real problems which stem from using non-original spares are simply not worth the risk.

Phil Bolton is a water industry specialist at Watson-Marlow Bredel Pumps.

Tel: 01326 370 370.

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