Wilden pumps - a safe option in coating production

Transferring coatings, resins and solvents around a production plant can prove to be a difficult process in respect of preventing leakage and the effects on the pump components

Leakage to the atmosphere creates potential hazardous and environmentally dangerous conditions, making fluid containment a basic necessity.

Furthermore, component wear reduces the working life of the pump, increases maintenance costs and contributes to lost production due to down-time.

Of the many pump types that can be considered for transferring fluids in the coatings and resin industry, the air operated double diaphragm (AODD) positive displacement pump can be described as ticking most boxes.

At the Valspar Deeside plant the pump of choice is the Wilden PV8 2inch SS ATEX Teflon fitted fully bolted AODD pump.

Over the past five years AxFlow has supplied upwards of three dozen ATEX certified Wilden AODD pumps to Valspar, the vast majority of which are being used in designated hazardous areas for pumping liquids ranging from low viscosity solvents through to high viscosity resins.

Valspar produces a wide range of coatings for different customers in the packaging industry but the make up in all cases is very similar.

The largest batch will be around 40m3 and smallest around 300litres.

According to a Valspar spokesman, the pumps are used for transferring raw materials into vessels and on the discharge side for re-circulating and filling off into IBCs and road tankers.

The objective is to shift raw materials and product quickly on demand.

High levels of pumping accuracy are not required nor are the pumps expected to handle temperatures above 50C.

There are some materials that have a high solids loading content and the Company does produce a lot of water-based products containing titanium dioxide.

However, this type of product does not present a problem to the Wilden pump as it flows well.

It is not a slurry, but more of a dispersion.

Gear pumps could handle this, but the plant engineers prefer the AODD as the uptime is good, plus components such as diaphragms are easy to change.

Some five years ago, the Valspar plant was equipped with a plethora of AODD pumps from many manufacturers, but it was Wilden that had the best reputation both in terms of performance and service support provided by AxFlow.

Thus, when it came to replacing ageing or damaged pumps a decision was taken to install Wilden AODD pumps, not only because of their superior performance but also because it made sense to standardise on one manufacturer of pump.

This, says Valspar, enabled it to reduce spare parts stockholding, standardise on procedures and have the ability to swap and change pumps if problems arose.

The Wilden PV8 pump can transfer almost any fluids and is suitable for operation in the most hazardous and difficult conditions.

It can transfer heavy, abrasive liquids and slurries equally as efficiently and effectively as fluids that can be damaged by high shear forces.

The other key factor in its employment is that because air operation is intrinsically safe by design, the pump can be used in hazardous areas where ATEX compliance or certification is required.

When running, the dynamic components that come into contact with the fluid are the two diaphragms which are connected by a common shaft, the two inlet valve balls and the two discharge valve balls.

The diaphragms act as a separation membrane between the compressed air supply and the fluid.

Driving the diaphragms with compressed air, rather than the shaft balances the load on the diaphragm which removes mechanical stress and therefore extends diaphragm life.

The valve balls open and close on the valve seats to direct the flow.

The absence of close fitting parts allows solids to pass through the pump without harm, whilst abrasive and viscous products can be pumped without any damage to the fluid characteristics.

Furthermore, the pump can run dry, self-prime and 'deadhead' without any adverse implications.

The primary wearing part of this pump type is the diaphragm, so it is essential that the correct type of material is specified for the media to be transferred in order to attain long working life and reduce maintenance costs.

For Valspar, AxFlow has supplied Teflon diaphragms.

In addition, reducing the stress to which the diaphragm is subjected will contribute to long diaphragm life.

In the case of the Wilden pump, the diaphragm is moulded in an 'operational' shape, such that stress concentration is minimised throughout its entire stroke length.

In contrast, traditional and dome-shaped diaphragms re-form as the pump operates, which induces high stress levels in the rubber and fabric from which the diaphragm is constructed.

One positive change has been the introduction of fully bolted pumps to replace clamp banded models as these are able to cope with very low viscosity fluids.

Given the opportunity, low viscosity fluids will find a weak point in the pump and in the Valspar experience, clamp banded pumps do have their shortcomings.

Valspar reports that the fully bolted pumps ensure trouble-free operation.

When it comes to maintenance Valspar places a relatively low priority on the Wilden AODD pumps as it has confidence in their ability to run for long periods.

The plant runs a batch production schedule on a 24/7 basis and it is common for individual pumps to run non-stop for 4 hours a day.

In fact, more often than not, it is only when the pump has reached break-down point that it is taken out of operation for servicing and two years' unbroken operation is not unusual.

For any processing plant not to experience some difficulties or challenges would be highly unusual and Valspar conforms to the norm.

One problem that has been experienced is foreign objects getting into the pumps and damaging the diaphragms.

The reason behind this was due to poor experience in cleaning the 'Y' strainers upstream of the pump units which allowed matter to get through to the pumps.

However, the company has recently instigated a programme whereby when a new pump is installed an in-line filter that is easy to maintain is fitted immediately before the pump.

The new filters are of a basket type and are very simple and easy to clean.

For the Valspar Deeside plant to satisfy its customers' requirements, it needs to be able to supply products on demand at all times.

The efficient transfer of raw materials, intermediates and finished products using AxFlow Wilden AODD pumps is making a significant contribution to the plant performance and meeting company targets.

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