Tips for Corrective Maintenance in Hydraulics and Pneumatics

“Innovation and product expansion is key, not only for the growth of individual business practice, but to boost growth, employment, productivity and competitiveness in South Africa. We have to align ourselves with the global market in order to gain a competitive advantage” says Seal & Gasket owner Allan Plotz.
In 2012, we purchased the Seal-Master 700, reported at the time to be the largest diameter CNC seal making machine in South Africa. The acquisition has allowed us to expand our product offering to provide comprehensive sealing solutions that can be customised to varying hydraulic and pneumatic applications. “The machine can manufacture seals with diameters from 5mm up to a maximum of 720mm and is able to turn various materials and compounds such as polyurethane, various grades of rubber, plastics and PTFEs” says Plotz. “The machine has immense capabilities and has allowed us expand our product portfolio to better support our original-equipment customers by providing range, quality and reliability that exceed their expectations.” 

The industry has seen an increasing need for dependability and longevity in a trade where there is an obvious lack of expertise and skilled professionals. The quality of each individual component is vital in optimising hydraulic and pneumatic capabilities. It is becoming increasingly difficult for companies to absorb the costs incurred from failures or maintenance. “We want customers to understand that compromising on quality components will be more costly for them in the long run. We also need to train operators to identify potential maintenance problems before they transpire, for example, for a seal to operate safely and efficiently, hydraulic equipment needs to operate within a specified maximum speed, temperature and pressure range.” One of Seal & Gasket’s core strengths is our ability to provide technical advice and support before and after the purchase. “Reliability can not only be determined by the product, but also the levels of service and support acquired by your suppliers.” 

In order to increase productivity and reduce breakdowns and costly downtime in hydraulic cylinders, Plotz stresses the importance of seal upkeep as a key area of preventative maintenance. “In order to increase the lifespan of equipment and components, industry players need to understand the direct correlation between each part.”

Plotz suggests the following quality control methods to avoid rod seal leaks in order to eliminate the need to replace cylinders and rods:

  • One of the major causes of seal failure is a damaged piston rod which is caused by misalignment. Poor alignment between the cylinder and the load will cause piston and gland bearings to be exposed to side–loading which will then cause damage to the rod or the surface of the tube, and therefore the seal. This can be an extremely costly exercise because a new piston rod is a customised part that’s made to order and cannot be repaired, but will need to be replaced after a complete strip down and rebuild of the cylinder.

    While there is no real solution other than cylinder review and accuracy in machine alignment, it is important to ensure that piston and gland bearings are correctly proportioned to support the cylinder loads and handle the thrust forces created by the application. It is also important to understand that cylinders are designed to provide linear force and that the maximum thrust of this force is limited by its rod diameter and overall length. In cases where Clients have requested a sealing solution to further prevent the issue of misalignment, we have identified and manufactured a profile ideally suited for heavy-duty mobile and stationary service, and that is highly resistant to side loading and insensitive to pressure spikes.
  • Make sure the seal housing is free from any damage that could possibly harm the seal. It is important to remove all sharp edges and burrs from metal parts, especially ports, grooves and threads over or through which the seal passes during assembly. All seal housing areas, as well as surfaces adjacent to the passage of the seal, must be cleaned to ensure that all metallic bits and other dirt particles have been removed.
  • To further avoid premature rod seal failure, it is important to lubricate all seals and components with clean operating fluid. Fluid contamination is often the result of water or air suspended in the fluid. Water affects the lubricity of the fluid and causes many seal materials to harden, crumble or disintegrate. In these instances, we offer a hydrolysis resistant polyurethane seal (HPU) as this material is more resilient to high water based fluids at higher temperatures. Heated air bubbles are also a common problem when dealing with hydraulic applications and are commonly caused by a rapid increase in hydraulic pressure. The intensely heated bubbles sit at the lip of the seal and cause small, damaging marks on the inner surface of the seal.
  • It is important for the seal to be the correct size, type and material. The choice of seal material is extremely important in eliminating problems caused by extreme temperature applications or where the seals may be damaged by chemicals. While a static seal such as a cylinder body O-Ring can tolerate swelling to a degree, the same cannot be said for a dynamic seal which will cause friction and faster wear if swelling occurs. The best solution is to ask your seal supplier for a material recommendation based on a particular fluid.
  • Seals must be stored (distortion free) in a cool, dry and dark place prior to fitting
  • Where the difference between a thread diameter over which the seal must pass and the seal diameter is small, use some form of protection over the thread, for example, a fitting sleeve made out of hard plastic
  • Where seals are fitted to pistons awaiting further fitting, it is important to make sure the seals are not subjected to misaligned or localised loading as this will cause deformation
  • Remember to flush the hydraulic system carefully before connecting the cylinder to it
  • Special seal designs should be considered when a severe flow restriction at the head end of the cylinder is accompanied by accidental pressure increases. This, together with an oversized rod, can cause high pressure leakages and rapid wear. We always recommend polyurethane seals as the most effective material to withstand this type of leakage.
  • We also urge the importance of understanding how the application works and the pressure it requires to better optimise efficiencies. For example, the cylinder may not work to its full capacity because some elastomer lip seals require a minimum pressure level to be fully energised. Your sealing specialist should be able to guide you in terms of what profile is required, based on the amount of pressure to be applied.

Further, it is important to identify that innovation does not only pertain to the product, but also to service efficiencies. “The Seal-Master 700, for which we have a dedicated and trained expert resource, allows for an exceptionally fast turnaround time so we can provide an express service to our hydraulic and pneumatic customers.”

It has also allowed for productivity and accuracy optimisation and developments which, according to Plotz, “are crucial to position South African manufacturers as highly competitive players in the local and global markets.”