Using the right oil sampling hardware helps ensure you're getting an accurate sample every time. Below we'll talk about the oil sampling equipment you need to take an accurate oil sample.
Quality Oil Sampling Hardware: Why It's Important
Coupled with the knowledge of how to take a proper oil sample, a lubrication specialist extracting a representative oil sample is only as good as his or her tools. Without these two things, you'll most likely wind up with a non-representative oil sample, which can have detrimental consequences down the road. Using the wrong or inadequate oil sampling hardware, taking oil samples from unsuitable locations, collecting samples incorrectly and even handling the samples improperly can all lead to an oil sample that doesn't represent the true condition of your equipment.
For example, taking an oil sample from the wrong location, such as a point downstream of a filter, won't show an accurate representation of the amount of wear debris or other contaminants in the oil, portraying the oil in the system as clean and eventually resulting in unexpected downtime. Conversely, using the proper oil sampling equipment by installing a correct oil sampling valve where needed (in this case, ahead of the filter) and extracting an oil sample there using the proper procedures will cost much less than any error resulting from incorrect sampling.
Proper oil sampling tools are also needed to prevent the sample and the system from being exposed to the ambient air, which contains airborne contaminants like water or particles. Sampling oil without opening the bottle can be done using the right oil sampling hardware. Having a correctly sized and properly cleaned bottle, a zip-lock sandwich bag, the right sampling port and valve, and a sampling device like a vacuum pump are all things you'll need to accomplish this.
Below we'll discuss the various pieces of oil sampling equipment you'll need to take a truly representative sample of the oil inside your machinery. These include oil sampling accessories like vacuum pumps, tubes and bottles; sampling ports, port adapters and gauge adapters; and sample valves for high- and low-pressure systems.
Oil Sampling Hardware: What You Need to Take an Accurate Oil Sample
While the procedure and method of oil sampling may vary depending on the type of application and machine you're sampling, oil sampling equipment can, in most cases, be applied universally.
Oil Sampling Accessories
- Sample extraction tube: A sample extraction tube takes oil from the valve or sump to the sample bottle. If it is used with a valve, it will have a probe or adapter fitting on the end. Typically, sample extraction tubing is made of low-density polyethylene, bought in bulk and cut to size as needed. Tubing comes in various sizes, most commonly 3/16, 1/4 and 5/16 inches. For more precise sampling or for sampling hard-to-reach machines, you can use microbore tubing. Microbore tubing refers to sample tubing in smaller diameters, typically around 2 millimeters.
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Vacuum pumps: Vacuum pumps are used to extract oil samples from pressurized systems not equipped with sampling valves. They are utilized in tandem with a flexible extraction tube to pull the fluid sample to the sample bottle. This tube can be fitted with sample port adapters if a sample valve is deployed. To set up the vacuum pump assembly, cut a piece of tubing long enough to reach halfway down into the vertical oil level height in the compartment of which you're sampling. If you are sampling from a valve, the tube must be long enough to reach the valve. On the other end, insert the tubing about 25 millimeters through the knurled knob on the vacuum pump. This is the pump location where you'll screw on the sample bottle below where you tighten the knurled knob to grip and seal the tube (do not overtighten).
Make sure your vacuum pump accepts the size of your tubing. The bottle should be threaded tightly onto the pump to achieve a vacuum-tight seal. It's best practice to place each bottle in a zip-lock sandwich bag (see the previous link) in advance to restrict particle ingression from the ambient air and dirty hands during sampling. Once the pump is assembled, follow the proper method for drop-tube vacuum pump sampling or valve and tube-adapter sampling. It's important to note that you should change the tubing each time you draw an oil sample to prevent cross-contamination.
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Oil sample bottles: Choosing the correct oil sample bottle depends on the application and planned oil tests. Before selecting a sample bottle, you'll need to consider features like bottle size, cleanliness and material. Bottles are typically made of materials in three categories:
- Opaque plastic: Opaque plastic like high-density polyethylene (HDPE) is one of the most common bottle materials on the market. You should try to avoid this material because it's difficult to visually inspect the sample due to its opaqueness (similar to a plastic milk jug). A less opaque polypropylene is also sold.
- Polyethylene terephthalate (PET): This type of plastic is completely clear and compatible with most types of lubricating oil and hydraulic fluids, including synthetics. Other clear plastics are sometimes used including polyvinyl chloride (PVC).
- Glass: Glass bottles are more expensive, heavier and come with the risk of breaking. Glass bottles can be cleaned and reused multiple times, and their cleanliness usually exceeds that of plastic bottles.
Speak with the lab to ensure you're using the correct bottle size for your sample. Bottle size is based on the type of fluid and the types of tests the lab will run. Most standard oil tests require the sample to be taken in a 100- or 120-milliliter bottle. Sometimes the test requires a 200-milliliter or larger bottle.
Finally, you'll want to confirm that your bottle meets ISO cleanliness standards to ensure the bottle doesn't add a reportable amount of contamination to the sample. Again, cleanliness depends on the type of test to be conducted and the objectives. Generally, the sample bottle should have a specific cleanliness level of two ISO codes cleaner than the target cleanliness objective. ISO 3722 provides a guideline for bottle cleanliness testing. The following cleanliness categories are frequently applied according to their contribution to the particle count:
- A clean bottle requires fewer than 100 particles greater than 10 microns per milliliter of bottle volume.
- A superclean bottle requires fewer than 10 particles greater than 10 microns per milliliter of bottle volume.
- An ultraclean bottle requires fewer than one particle greater than 10 microns per milliliter of bottle volume.
It's important to flush all sampling hardware (hoses, tube, valves, etc.) to get a truly representative sample. Flush five to 10 times the dead space volume before you collect your sample. Flushed oil can be collected into a purge bottle and returned to the system.
Sampling Ports
Two of the most critical aspects of the sampling process is where and how oil samples are collected. However, ports (and valves) aren't always where you need them to be. In fact, 71 percent of people reported to Machinery Lubrication magazine that they had to modify their equipment to enable oil sample ports and valves to be accurately located in order to obtain an accurate sample.
Installing multiple ports in strategic locations can isolate components to help troubleshoot the source of problems after abnormal conditions are found. Primary sample ports should be positioned where routine samples are taken to get the best overall assessment of fluid and machine condition. They are used for monitoring oil contamination, wear debris, and the chemical and physical properties of the oil. Primary sampling port locations vary, but for circulating systems they should be located on the return line before the fluid enters the sump or reservoir.
Secondary sampling ports can be placed strategically on a system to isolate components. This helps you localize the root cause of contamination by looking at individual components. An oil sample from the secondary port location should only be taken when the sample from the primary port detects an abnormal reading and you need to investigate the root cause further.
A good sample port is designed to draw samples from the most representative areas on the equipment and under normal operating conditions. This is done by using gauge adapters, port adapters and sample ports with pilot tubes (in the case of sumps and tanks). Below are examples of sample valves positioned at various locations on circulating and non-circulating systems.
Sometimes a machine's design or operating environment requires you to install a remote oil sampling port using line extensions. These may be necessary to effectively take samples for condition monitoring during runtime conditions. Many machines can't be easily accessed during normal operating conditions, but yet they may be the most critically important to sample. Cooling towers are a good example. They are critical and also difficult to conduct routine condition monitoring. Modifying cooling towers with remote sampling ports helps ensure they are properly maintained.
Sample Valves
Sample valves are installed into ports located on sumps and oil circulating lines for clean and efficient oil sampling. This achieves a controlled, fixed sampling location. Sample valves can help prevent leakage and accidental sample contamination. They also don't interfere with the machine's normal operation. As such, samples can be taking during normal operating conditions, which improves the quality of the sample.
Depending on your system, you might need to use multiple pieces of oil sampling hardware with the appropriate valve. For example, high-pressure hydraulic systems require a pressure-reducing valve, sample port adapter and hoses. A low-pressure system may demand a vacuum pump with a valve adapter to draw an oil sample. There are several valve options to consider:
- Portable high-pressure valves: High-pressure systems are difficult to sample during operation for safety reasons. Pressure must be reduced with either a portable pressure reducer (attached to the main sampling valve) or with stainless-steel helical tubing to lower the pressure. Be sure to get expert advice on the proper oil sampling hardware and procedure.
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Minimess valves: many consider the minimess or probe valve considered the best valve for taking a consistently accurate sample. Minimess valves should be installed on an elbow if possible for lines with high fluid velocity. To draw a sample, attach the probe fitted to the tube protruding from the sample bottle to the valve to let the oil flow into the bottle. Probe adapters can also be used. The probe unseats the mechanical check (spring-loaded ball) located inside the valve. As the probe is engaged, it pushes the check in the valve off its seat, allowing fluid to flow through. The vented bottle cap forces out air or exhaust. Minimess valves can be used on low-pressure systems. Low-pressure systems require a soft valve seat to avoid leakage.
Portable minimess valves can be installed onto the female end of a standard quick-connect coupling. The male end is permanently fixed to the pressure line at the proper sampling location. Just like a regular minimess valve, as the female end is threaded onto the male end, the check inside the valve is depressed, allowing fluid to flow. Portable minimess valves can be utilized on both low- and high-pressure lines as long as a pressure-reduction valve or a helical coil is used.
- Ball valves: Like minimess valves, ball valves should be installed on an elbow on low-pressure systems. Ball valves let you start, stop, adjust and direct flow or prevent backflow. Make sure the ball valve is flushed before taking the sample.
Other sampling valves are sold for specialized applications and needs. These include the valves shown and discussed below. Advantages to many of these models include a tethered dust cap to prevent contamination and oil leakage after sampling, the ability to also bleed air, and minimal dead volume. Common disadvantages include having only one or two sealing features, the inability to be used as a diagnostic port for periodically installing sensors and transducers, and the risk of damage to the "soft-seat" design in high-pressure conditions.
- Stauff sampling valve: Stauff sampling valves come in five models with maximum operating pressure ranging from 5,800 to 9,000 psi. The valve design provides you with three sealing techniques to protect against oil leakage: a dust cap oil ring seal, an internal valve core hard-seat seal and a dust cap internal probe seal.
- Circle-seat control valve: The P-500 series sample-and-bleed valve has an operating pressure of 0 to 3,000 psi. To draw a sample, turn the valve head one-quarter of a circle to allow the oil to flow into an open bottle.
- Fluid line sampling valve: Wear check oil sampling valves on fluid lines have an operating pressure of 0 to 600 psi and allow for a sample to be drawn into an open bottle by depressing the valve button.
- Parker aerospace sampling valve: With a rated operating pressure range of 30 to 5,000 psi, these valves provide good sealing at low to medium pressure. A sample can be drawn using a hand-held probe device connected to a tube inserted into the mouth of an open bottle. The tube can also be attached to a port on a bottlecap or connected to a vacuum sample pump.
- Taylor sampling valve: Taylor valves are available in brass (with an operating pressure up to 2,000 psi) and stainless steel (with an operating pressure up to 5,000 psi). Soft-seat technology makes these valves good for sealing at low to medium pressure.
- Eaton sampling valve: The Eaton FD 150 oil sampling valve should be installed in low-pressure dynamic fluid lines and return lines. Operating pressure for the Eaton FD 150 is 0 to 300 psi. It should be noted that this model is not intended for aerospace applications.
- Checkfluid sampling valves: These valves come in three models: KP Series Pushbutton, KST Series and LT Series (drain port sampling device). The KP series has a sampling pressure range of 5 to 750 psi and the KST has a sampling range of 5 to 4,000 psi; both with maximum operating pressures of 6,000 psi. The LT series has a sampling range of 0 to 125 psi with a maximum operating pressure of 1,000 psi.
- Caterpillar sampling valve: The S.O.S. oil sampling kit is approved for use by Caterpillar and is standard on its products. The valve uses soft-seat technology to enable good sealing at low to medium pressure and allows for sampling in nearly any orientation.
Improvements to Oil Sampling Hardware
Over the years, technology and ingenuity have improved upon the designs and availability of oil sampling hardware to make sampling easier to obtain and more representative of system and fluid conditions. Two of the most notable pieces of oil sampling equipment that have been recently introduced are the Ultra Clean Vacuum Device (UCVD) and Luneta's Condition Monitoring Pod (CMP).
The UCVD is an advanced sampling bottle designed to hold a pre-established, pre-distribution vacuum, making it "ultraclean" by being free of almost all moisture and contaminants. It works by attaching the bottle's nozzle to a sampling tube, inserting the other end of the tube into the sampling valve and turning the nozzle to release the vacuum, which draws oil into the bottle. This method actually eliminates the need for a traditional hand-pump vacuum pump and can be used on any lubricating system, including pressurized systems.
The Condition Monitoring Pod is a multifaceted piece of equipment that lets an inspector perform multiple tasks from the same port. Described as a "multi-parameter inspection pod," the CMP is an oil sight glass and sampling port engineered into one piece of equipment. The CMP lets you readily view oil levels, color and clarity, aerating and foaming, corrosion, varnish and wear debris. Additionally, you can draw an oil sample from the built-in, vacuum pump-compatible sample port. The CMP includes a stainless-steel pilot tube that can be bent to the desired sampling location inside the machine.
