Fluid condition monitoring can be used to assess not only the condition of hydraulic oil, but also of the engine. Service intervals can then be matched to the actual condition of the machine. Results from the analysis can be used to extend the life of engines and hydraulic systems and predict faults before they occur. Experience at the Port of Tacoma, Wash., epitomizes this concept.
A potential for savings
Much of the yard equipment at the Port of Tacoma is owned and operated by the port authority or leased to private stevedores. Each machine operates for 200 to 2500 hours annually. In an attempt to reduce maintenance and extend the life of its container handling straddle carriers, Figure 1, authority officials first experimented with hydraulic fluid testing in 1994.
Initially, a testing system was tried with the hydraulic fluid on two older Drott hydrostatic straddle carriers and two Kalmar lift trucks. The straddle carriers are huge machines, which becomes evident when observing the size of the man standing at far left in the picture. These carriers operate at pressures to 4000 psi and have two 75-gal reservoirs supplying Dynapower piston pumps, manufactured by Eaton Hydraulics. The lift trucks have a lower operating pressure of 2900 psi and 80-gal tanks fitted with Vickers piston pumps. The oil used is Chevron AW MV ISO 46 hydraulic fluid.
Particle counting
The first step was to assess the contamination of the hydraulic fluid by particle counting, which detects the size and quantity of contaminants in the fluid. The framework is provided by ISO 4406, which gives two measures: the total number per ml of particles 5-µm and greater in size and 15-µm or greater. This is expressed as two numbers, for example 17/15, each of which denotes a range of the actual number of particles (see Table 1, below).
Based on the experience of our oil analysis department, the port authority officials determined that the target cleanliness level for the straddle carriers and lift trucks should be 14/11 and 15/13 respectively, the difference reflecting, among other conditions, the higher operating pressure of the straddle carriers.
The first test results revealed particle counts for the straddle carriers of 20/15 and 20/16 the lift trucks came in at 21/15 and 21 /16. We estimated that the life of the hydraulic systems could be extended by three and a half times on the lift trucks and four to five times on the straddle carriers by reducing the amount of particulate contamination.
Benefits of success
The next step was to improve the hydraulic systems' filtration systems. We installed a depth-type kidney loop filtration system (including a low flow rate filter with a high particle capture performance) on each machine— a total cost of about $1500 per lift truck and $5000 per straddle carrier.
The initial results were very impressive: particle counts dropped to the target levels, and some tests returned results as low as 10/9. Not surprisingly, annual maintenance costs subsequently fell by 45% on one straddle carrier and by 97% on the other. This machine had been costing Port of Tacoma $45.52 per operating hour just in maintenance costs!
Similar benefits were gained with the lift trucks. They exhibited a 65% to 71% decline in particle count, with maintenance costs per operating hour down to 77¢ for one machine and 86¢ for the other.
Engines also benefit
Port Authority officials then shifted their attention to 21 Valmet/Sisu straddle carriers. Average engine life before overhaul on these machines was 7200 operating hours, and their maximum life was 9000 hr. Engine oil was changed every 250 hr and had an average ISO cleanliness code of 19/16.
The target to extend engine and oil change intervals was determined be an ISO particle level of 15/12. We fitted the machines with new filtration systems, and the result was oil change intervals extended to 750 and 1000 hr.
Furthermore, such favorable performance and test reports prompted the Port of Tacoma to push the period between engine overhauls out to 21,000 hr. At the beginning of last year, the equipment's Volvo engines had reached 16,000 service hours and were expected to reach the 21,000-hr target set nearly six years ago. Some of the engines have lasted even longer. Officials attribute much of this success to maintaining particle counts at or below target levels. In fact, ISO levels of 14/11 and 13/10 now are common.
Investment pays off
Tacoma Port Authority's cost of replacement hydraulic components fell by 59% within four years of implementing the testing and filtration systems. The total cost of maintaining its fleet of 21 straddle carriers fell by $209,000/yr - and this is after including the costs for oil analysis and filtration system retrofitting. In addition, officials claim to have all but eliminated unscheduled downtime for these machines.
Preliminary tests are now carried out on site. A sample of hydraulic fluid is taken from a gauge tap adapter that is installed just before the return filter, Figure 2. The fluid sample flows through a microbore hose with swivel fitting. With oil at operating temperature, a 4-oz bottle is filled and examined by a technician, who has a small lab set up on-site. The oil is diluted with hexene and pulled by vacuum through a patch, which the technician subsequently views through a microscope. If anything out of the ordinary is observed, a second sample is taken and sent off for an accurate particle count and viscosity check.
We installed filters for the engine oil as well. Fluid enters from the cam galley and returns to the oil pan. Two samples of hot oil are taken. One is sent to an Exxon/Mobil lab for spectrographic analysis, and the other goes to our lab for particle counting. This procedure is conducted every 250 to 500 operating hr, and the oil and filter are changed every 1000 hr.
For more information, contact By Bruce Anderson, General Manager of Contamination Control Engineering Co. (CCECOLab & Filtration), Kent, Wash., at (253) 872-5500, or visit cceco.net.