Expert Advice
The Importance of Visual Inspections
Buckets are important when changing oil, but when the bottom of the bucket is not visible, another route must be taken.
The condition-based maintenance team recently collected an oil sample on a No. 2 condensate booster pump motor as part of a routine sample collection. While pulling the sample, the oil was observed to be dirty. Due to high vibration on another booster pump and the fact that the unit was coming off in a couple of days, the team decided to let it run.
A few days later, vibration data was collected on the No. 2 motor. Because there were no indications of a vibration problem and a unit outage was scheduled in three days, maintenance personnel decided to let it go and changed the oil on the scheduled outage.
While changing the oil, a unique situation occurred that reiterates the importance of using a clean bucket every time an oil change is performed. During routine procedure, at the conclusion of draining the oil into a clean bucket, the oil is visually inspected for any debris or unusual matter. In this case, the oil was so dirty that the bottom of the bucket could not be seen and a visual inspection was not possible. However, being aware of the importance a visual inspection has on the life of the equipment as well as the possible monetary savings of any findings encountered, we transferred the dirty oil into another clean bucket so visual inspection could be achieved. During this inspection, a steel pin was found.
A maintenance supervisor was contacted, and after examination, he suspected this was an alignment pin from the bearing housing. With this information, further inspection was necessary and upon pulling the sight glass, another pin was found. As a result, maintenance pulled the bearing out and observed that the dowel pins came from the bearing halves.
As a result of routine procedures, utilizing clean buckets and innovative thinking, condition-based maintenance had a great save!
Check the Flow RateOnce a hydraulic problem occurs, the pump should immediately be changed. However, it's recommendable to first conduct some initial tests! An appropriate test for variable displacement hydraulic pumps is to check the flow out of the case drain line. The oil that bypasses the internal vanes or pistons in a pump will flow out of the external case drain. On piston pumps, normal flow rate is one to three percent of the maximum pump volume. The normal case flow on vane pumps is slightly higher, three to five percent. For example, if a 30 GPM piston pump is used, then one-third to one GPM should return to the tank through the case drain line when the pump is performing accurately. The flow should always be checked when the pressure is at maximum, because that is when the highest case flow will exist.
The flow can be checked in one of two ways. With the hydraulic system off and the pressure at zero PSI, the line can be removed and run into a container of known size. If possible, secure the line to the container because holding the line may create a safety hazard. Turn the pump on and record the amount of oil that flows into the container for one minute.
The second method is to temporarily or permanently install a flow meter in the case drain line. This will provide an easy, accurate method of checking the flow rate while the machine is operating.
When the case flow reaches 10 percent of the maximum pump volume, the pump should be changed. In this example, the pump should be replaced when the flow rate is three GPM.
Sometimes oil leaks on large machines, such as paper machines, can be hard to find. When the oil level in the reservoir drops but no puddles appear, look for a leak that is running directly into a "u" drain or other sewer openings. If you use oil coolers and the oil pressure is higher than the water pressure, disconnect the water side of the cooler, turn on the oil pumps and see if oil drains from the water lines, indicating a blown cooler. Inspect Level Gauges
Inspect the vent hole in column-type vented level gauges routinely. In dirty environments, the vent hole can easily become plugged, causing an air lock in the gauge headspace. This will result in a false oil level (higher than reality) in the gauge. Many prefer dual-port gauges (vented to the headspace) instead.
Place the adhesive labels around the bottom half of oil sample bottles. This makes it easier to see the fluid as it nears the top or neck of the sample bottle. Check PMs for Problems
Our plant has experienced problems with one of our many five-ton overhead cranes, which are integral in our material-handling process. The hoists are 20 feet above ground and carry massive rolls of film. Critical maintenance downtime pushed us to a long-overdue reliability inspections.
It was discovered that one of the gearboxes retained sludge deposits in its casing, while another one was noisy. It was noted that one gearbox was grease-lubricated, while the others were oil-lubricated.
Preventive maintenance was performed on two gearboxes with the same oil, which wasn't even the correct viscosity oil. Not only were we lubricating this hoist incorrectly, but we also employ eight others which were lubed in the same manner. This created a safety hazard in addition to lost production.
Bottom line: Double-check the validity and accuracy of all PMs. Just because a PM exists doesn't mean that it's correct.
Oil Mist for Contamination Control
In bearing applications where high contamination levels are a concern, consider converting grease lubrication systems to oil mist lubrication. Oil mist systems are slightly pressurized, which helps to exclude contaminants. Use a pure mist system for rolling element bearings and purge mist for gearboxes and journal bearings.
Seal it Out
To keep the end of your grease gun clean and prevent contamination from entering a bearing when lubing the bearing, place a plastic cap over the end of the lube head. Caps come in all sizes and the half-inch provides a tight seal to keep out everything from dirt to water.
Purge Before Installing
Purge all new grease fittings with a grease gun before installing them on the machine. Use the same type of grease that will be used later for regreasing. This practice removes any dust, burrs and other debris that has collected inside the grease fitting. It also reduces the risk of cross-contamination between different grease products.
In time-critical situations where real-time infrared thermography is impractical and thermocouple/recording equipment cannot be installed, consider temperature-sensitive tapes. These tapes are manufactured in a variety of sensing ranges and will clearly record the peak temperature that a machine area reached since the tape was first applied. A quick visual check is all it takes to read the "paper thermometer".