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System contamination is a leading cause of forklift hydraulic pump failure. Hydraulic repair is an important process to do to improve your equipment’s longevity. There are multiple causes for system contamination including:
- Improper fluid flushing after repair
- A non-thorough cleaning job is performed
- Technician does not remove contaminants from hydraulic system
- Technician cannot see the oil cleanliness level before or after repairs
Phases of Wear
Wear on a lift truck begins as soon as it is put into use. Some wear can be identified through regular maintenance checks, while other wear may not be noticeable until later. As a lift truck gets older, it may show signs of wear during routine maintenance. Oil analysis can help identify potential issues. At this stage, it may be possible to keep the lift truck operating normally by addressing the wear. However, if too much wear has occurred, it may be necessary to replace components or perform an overhaul. The task of a service technician is to monitor the lift truck and make any necessary changes when wear or contamination is detected, using regular maintenance practices and tools like filter caddies. An effective oil analysis program should allow for early detection of issues that may require a flush, allowing for a simple oil change rather than a more extensive procedure. The success of this detection depends on taking oil samples at the right intervals and using appropriate laboratory tests.
Phases of Wear Table
| As Time Progresses | ||||
|---|---|---|---|---|
| Operating Normal | Operating Normal | Some Symptoms Appear | Performance Issues | Failure |
| Non Detectable Wear | Some wear detectable through fluid analysis | Point of no return | ||
| Visible wear, changes in behavior | Very visible symptoms and wear | Forensics | ||
| Objective is to increase the operating time with non detectable wear through standard maintenance practices, including conditioning units (filter caddy) and an oil analysis program. | ||||
Causes of Hydraulic System Failure
According to industry data, a forklift hydraulic pump failure, which occur at a rate of 70-80%, is likely not due to design issues, but rather to contaminants such as water or lubricant degradation. These contaminants can be introduced through various means, including improper maintenance and service procedures, the addition of fluids, the replacement of failed components, and dirty equipment or parts storage. Contamination can also occur due to ingression, such as through leaky cylinder seals or poorly maintained reservoir vents, as well as due to internal wear and part failure. Additionally, chemical reactions between lubricant additives, water, air, heat, and metallic particles can also contribute to contamination.
Contaminant Caused Hydraulic System Failure
When there are high levels of contaminants in a hydraulic system, it can lead to wear on all moving parts and erosion of soft metals. Chemical reactions between additives and water or incompatible oils can also cause etching, which reduces pump efficiency and increases the likelihood of internal leaks and high temperatures. High temperatures can reduce the life of oil additives and impair the lubricant’s ability to separate moving parts, and metallic particles can contribute to the rapid oxidation of the lubricant. This destructive process can result in the failure of major components, such as pumps or cylinders, and when a failure does occur, it can release millions of metallic particles, fibers, and contaminated oil throughout the system. Simply replacing the oil in the reservoir is not enough to fully restore the system.
Double Oil and Filter Change
This process is intended for lightly contaminated systems or those with degraded fluid, and should not be used for systems that have experienced major component failures. It is worth noting that replacing a large volume of oil and disposing of contaminated oil can be costly, and if the oil is not degraded, this would be a waste since it is only contaminated and not degraded. To “condition the fluid” by removing particles and water, a filter caddy can be used.
This process involves an initial oil drain and filter change to remove a significant portion of contaminants and degraded fluid. The system is then filled with pre-filtered oil and the fluid is circulated at low pressure until it reaches operating temperature, each hydraulic function has been operated three full cycles, and the fluid has been turned over at least five times. The oil is drained again, the system is refilled with filtered oil, and the filters are changed a second time. After the fluid has been circulated, each circuit has been operated three full cycles, and the system has warmed up to operating temperature, an appropriate oil sample should be taken to evaluate the success of the flush.
Mechanical Cleaning
When a forklift hydraulic pump failure or cylinder failure has occurred, it is necessary to include mechanical cleaning as part of the flushing strategy. This involves using a pneumatic projectile gun and sponge projectiles to clean tubes and hoses, as well as disassembling other components for cleaning using brushes and clean solvents. It is important to also mechanically clean the reservoir to remove any residual contamination particles. While mechanical cleaning can be labor-intensive, it is the most effective way to restore the system to reliable operation after major mechanical failure.
Component Cleaning Process
Reservoir Cleaning Process
- Ensure absolute cleanliness in all of the following procedures.
- Clean the top of the filter housing, cap, and surrounding surface to avoid adding extra contaminant.
- Remove the filter housing cap, filter element, and element bowl to allow access to the interior.
- Use a filter caddy to pump the fluid from the reservoir to a storage container to dispose of.
- Remove all remaining oil from reservoir.
- Remove and get rid of the suction strainer.
- Remove and get rid of the reservoir breather.
- Clean the reservoir to remove all contaminants.
- Clean all accumulated metallic particles from the magnetic plug and reinstall.
- Install new reservoir breather.
- Install new suction strainer.
- Cover the reservoir openings until ready to perform flushing operation.
Cylinder Cleaning Procedure
- Ensure absolute cleanliness in all of the following procedures.
- Clean the external surfaces using industrial, residue free wipes prior to loosening fittings and components.
- Cover all connecting hose and cylinder openings immediately with caps to prevent dirt and debris from penetrating the system.
- Disassemble the cylinder and clean all parts with filtered petroleum based solvent to remove all contamination particles. Ensure that you clean the seal grooves, gland nut, and port threads.
- Install new seal kits.
- Fill the cylinder with filtered hydraulic fluid. This will displace the air and reduce the risk of air compression in the cylinder that can cause dieseling during initial pressurization at start up. Dieseling will result in damage to the cylinder and seals.
- Plug all ports and reinstall into the equipment.
