Repairs revitalize papermill system

Removing water at the earliest stage in the papermaking process speeds up the formation of a hard, strong, consistent sheet whilst also reducing web breaks and water removal costs and this is typically performed by low vacuum fans. However, further along the production line there are stages where higher vacuum levels are required to remove water and assist in the drying process. These duties are often performed by Nash liquid ring pumps as they are suited to adjusting the vacuum levels to optimize water removal and deliver maximum efficiency.

Of all the Nash liquid ring pumps operating in paper mills, the CL series are the ones that are most widely-used. They are continuously operating and so have to be hardworking and reliable. So when AxFlow Finland took delivery at its Kotka workshop of a Nash CL pump from a paper mill in northern Finland, they were not surprised to learn that the pump had been operating for over 45 years.

Patience is a virtue

The pump was delivered to the workshop as a complete unit, and due to its size, a crane had to be used to transfer the pump from its transporter into the workshop. The first task was to strip the pump down in order to determine the cause of failure (Figure 1). This was not a straightforward task and it took around five days to complete the job and record details of the state of all the components. Because of its age and long operating life many of the parts had fused together, so the engineers undertaking repairs had to be patient. 

Figure 1. Repairs being carried out at the Kotka plant.

Once the pump had been opened up, it became clear that the bearing rollers at one end of the shaft had failed due to overheating, (Figure 2) and the most likely cause was a lack of lubrication. The bearings at the other end were in a reasonable condition as there was sufficient lubricant in the gear box. In order to remove the damaged bearing rollers the complete bearing housing had to be cut free from the end plate and a replacement bearing housing installed. The condition of the original end plate was a cause for concern and beyond repair, so the customer supplied a replacement along with the pump, and to bring this up to specification it was cleaned and given a wear resistant coating.

Figure 2. The rollers' bearings were badly worn as a result of overheating.

Refurbishment and cleaning

Whilst there was little sign of wear to many of the components, due to the non-aggressive nature of the media being pumped, a programme of refurbishing and cleaning the pump was undertaken prior to the installation of the new bearing rollers and end plate. The exacting process of recoding the condition of components during strip down enabled AxFlow's engineers to identify where refurbishment work was required and also highlight to the customer the remaining lifespan of components for maintenance purposes. It's a procedure the company undertakes on all repair jobs. In the case of this pump, failure was down to the absence of oil in the roller bearings, so the pump had performed extremely well over its many years of service.

AxFlow Finland's knowledge of Nash liquid ring vacuum pumps and its engineering skill sets enabled it to take on such a challenging project “Nash places considerable emphasis on the quality of its pumps and demands that its suppliers are suitably qualified to undertake repair and maintenance of its products,” says Sami Salonen, AxFlow technical account manager. “AxFlow has extensive engineering facilities together with the necessary qualifications and approvals from Nash to undertake this type of work and provide a minimum two year warranty. For this particular job we had to develop specialist tools.”

Condition monitoring

A key service that AxFlow Finland offers to Nash pump users is condition monitoring. AxFlow engineers go to the plant and attach a purpose-designed flange to the pump inlet ports. Once the pump is rotating they can measure how much air is coming through the holes in order to measure vacuum levels. Knowing the area of the holes enables the engineer to determine how much air can be sucked. With these results, a pump curve can be created so the actual performance level can be compared against the designed performance level. Alongside this service is the provision of hydroscopic inspection, which reveals the condition of components.

Figure 3. AxFlow's new repair and sales facility in Kotka, Finland.

Having invested in an expanded service and repair centre in Kotka in late 2015, AxFlow now has the heavy lifting, machining and cutting edge engineering resources, enabling it to provide extensive services. not just for the pumps within its own portfolio, but for many other types and brands.