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Sampling Guidelines

Sampling Frequency

The proper sampling frequency balances the costs associated with oversampling on one hand with the frequency necessary to eliminate unscheduled downtime. The goal is to sample only as much as required to ensure the reliability desired, no more and no less. However, determining the proper sampling frequency depends on many variables such as equipment value, system criticality, operating environment, equipment condition, and equipment stress. U.S. Lubricants’ Machine Health ServicesTM can conduct a detailed plant audit, determine machine and system criticality, and help you develop and implement a comprehensive oil sampling plan and process. In collaboration with our Contract Lubrication Services team, we could manage, staff, and perform the lubrication process in your plant.

Sampling frequency should be higher when…

Equipment value is high or the asset is custom-made and requiring long lead times to replace system criticality is high (systems that are critical to equipment operation, would require significant downtime to repair, could cause unsafe conditions for operators, etc).

Operating environment conditions are poor (dusty, or humid/wet conditions, high temperatures, harsh chemicals). Equipment operating in dusty and dirty off-road environments, as well as humid and wet conditions, will require sampling on a more frequent basis due to the increased amounts of airborne particles that can ingress into the fluid system, and the higher chance of moisture contamination. Fluids operating at higher than recommended temperatures tend to significantly reduce in viscosity as temperature increases. This can affect the lubricating properties and lead to increased component wear and heat generation. Fluid systems working with harsh chemicals can react more seriously to moisture and debris contamination, and therefore, should have tighter limits on fluid contamination. This can be monitored through more frequent sampling.

Equipment is new (in the wear-in phase), or old (in the wear-out phase).

Fluids are old (in the wear-out phase). Lubricants deteriorate due to the continuous loading and unloading, heating and cooling, and due to contaminant and debris accumulation.

System is stressed. Systems experiencing heavy loading, rapid cycling, and high operating pressures, (such as those in construction, forestry, agricultural, and mining applications) will require sampling more regularly, as they put stress on the lubricants used. This, along with the wear on seals and wipers, will increase the contamination risk. Lubricants in low speed gearboxes will normally require less sampling due to lighter duty work, slower speeds, and minimal pressure. Systems that experience only periodic loading or are not in continuous operation will normally produce less wear. However, the fluid is also more susceptible to moisture contamination since the system may not be reaching the temperatures needed to evaporate moisture.

Locating Sampling Valves/Ports

In-Line Sampling

In-line sampling valves are the easiest and most convenient method for sampling oils, lubricants, and coolants, while providing consistently clean fluid samples. Sampling valves should be installed in turbulent areas of the system, such as in elbow connection or sharp bends, to ensure particles are thoroughly mixed in the fluid. Primary sampling valves are typically located on the return line before the reservoir, where it can capture oil after passing through the entire system. Most samples should be taken through these primary sampling valves. Secondary sampling valves should be located downstream of critical components and upstream of any filters, in order to monitor the wear of individual components. In case high levels of wear metals are found from primary sampling valves, sampling from the secondary sampling valves can identify which component is producing excessive wear. Sampling valves may also be used to monitor the effectiveness of filters. Installing a sampling valve before and after the filter, allows fluid to be analyzed from each valve to measure the filter’s efficiency and determine whether servicing is required.

Reservoir Sampling

Generally, sampling from a reservoir should be avoided. When necessary, use a tube extended valve. Ensure the tube is positioned to draw active oil and avoid sampling oil from the top, sides, and bottom surfaces of the reservoir as this oil is less active and could result in false readings. Positioning the tube to draw oil close to the inlet will help capture the most representative oil.

Remote Sampling

On large equipment or for added safety and convenience, install a remote access kit to allow sampling from a more practical location. Remote access sampling valves allow sampling to be performed by a single individual more safely and much more quickly, compared to sampling from hard to reach valves located in proximity to hot, sharp, or moving parts.

To ensure a good sample…

  • Avoid sampling downstream of filters as filters will remove the particles intended to be captured for analysis
  • Remember that sampling upstream of critical components will not provide condition data for those critical components that are downstream
  • Avoid sampling from reservoir bottoms or sumps, as this is where the particles settle and can result in elevated levels of wear particles and prompt unnecessary equipment maintenance
  • Sampling dead or static fluid should be avoided as this oil does not circulate through the system as often as oil in the active zones and can result in fluid readings that do not reflect the true condition of the system. This is way it is important to properly purge the valve of static fluid before capturing the sample for the lab.
  • Sampling cold fluids is not recommended as this does not reflect the condition of the system at operating conditions and if the system has not been running, the debris can settle from the static fluid resulting in a fluid sample that is not representative.

Comparing sampling valves and other sampling methods

Complete and Accurate Sample Data

Complete and accurate sample data should be submitted with each sample sent to the oil analysis lab. This data should include the following:

  • Company name and address
  • Unit number
  • System make and model
  • Miles/hours on system
  • Miles/hours on oil
  • Miles/hours since overhaul
  • Date sample was taken
  • Brand and grade of oil used
  • Oil added (make-up oil), quantity and date
  • Contact name (person to contact with results), email, phone number fax number and mobile (for emergency notifications)

This information is invaluable to the oil analysis laboratory, since it is considered heavily when maintenance recommendations are made. For example:

Miles or hours since overhaul - A new or newly overhauled machine showing relatively high levels of wear metals in the oil is perfectly normal when break-in wear is considered.

Miles or hours on oil - Oil samples with low miles or hours containing high wear metals indicate a high wear condition, whereas the same metal levels in a sample with high miles or hours may or may not be considered critical.

Oil added (make-up oil) - Engines or lubrication systems using excessive amounts of make-up oil will tend to show lower wear metal levels due to the diluting effect of the make-up oil.

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