Minimizing the Risk of Hydraulic Cylinder Contamination

Microscopic Particles Cause Catastrophic Failure

It is a common scenario for machinery using hydraulic systems for transmitting power: a microscopic solid particle causes catastrophic failure of a component. According to industry experts, contamination causes 65-90% of all hydraulic system failures. The malfunction may be intermittent, requiring extensive troubleshooting to identify the faulty component.

Once technicians identify the component, they must remove it for repair or replacement—a further time-consuming and often messy task. Throughout this period, the machinery remains out of service, leading to lost productivity and associated profits. To prevent a recurrence, engineers investigate the contamination source, and they often suspect the cylinder as the primary culprit.

Due to their relatively large internal volumes and manufacturing processes, new or repaired cylinders have earned a reputation for harboring destructive hydraulic fluid contamination. As a result, when a sensitive valve or pump fails, operators often blame the cylinder manufacturer.

Preventing Hydraulic Cylinder Contamination

Cylinder manufacturers must create and follow strict processes to prevent a hydraulic cylinder from contributing to the failure of other system components such as valves and pumps.

Step 1: Identify Contamination Types Specific to Cylinder Manufacturing

The first step is to identify the common types of hydraulic system contamination specific to the manufacturing process.

• Category 1 – Hard Particles: Hard particles include various types of metal, such as steel, iron, bronze, or aluminum, which may be generated during cutting, machining, grinding, or welding. It also includes dust and dirt. Airborne dust can settle on the surfaces of the internal cylinder components before assembly. Granular absorbents are especially troublesome because they swell and clump when oil is absorbed. Larger hard particles can cause sudden and severe damage, such as cutting seals and scoring metal surfaces. Smaller hard particles, also called “silt,” can be equally destructive but gradually cause wear and damage over a longer time period.
• Category 2 – Soft Particles: Sources of soft particles during cylinder manufacturing include rubber or urethane seals, composite bearings, and cloth fibers. These soft particles typically cause failure by clogging orifices or small passageways.
• Category 3 – Water: Water can be introduced from a humid environment or component parts that are not fully dried after cleaning, and it can cause corrosion and microbial growth.

Step 2: Stop Hydraulic System Contamination at the Source

After identifying the potential sources, the cylinder manufacturer can take steps to prevent building contamination into the cylinder during the assembly process. Although cutting and machining processes are necessary, the parts can be cleaned thoroughly. Work surfaces, storage locations, and material handling devices can be kept free of dust, dirt, and metal particles. Parts that have been cleaned can be kept in sealed plastic bags or covered with plastic to prevent re-contamination.

Climate control and air filtration systems can limit airborne dust and humidity in areas where cylinders are manufactured. Implementing procedures to completely dry parts after cleaning can ensure the moisture does not become a contaminant. Because common shop rags and disposable towels are notorious for shedding lint and fibers, selecting lint-free shop rags, disposable wipers, and absorbent mats can limit the introduction of soft fiber contamination. Granular absorbents should never be used in a hydraulic component manufacturing facility.

Step 3: Remove Contaminants That Eluded Preventative Measures

The last line of defense is to remove any hydraulic cylinder contamination that eluded the preventive measures before providing the complete cylinder to the customer. Functional testing is standard to check for internal or external leaks and ensure the cylinder provides the correct stroke. As the cylinder is cycled during the test procedure, hydraulic fluid flushes out contamination built into the cylinder.

While it is beneficial to remove particles from the cylinder, the result is a spike in the contamination level of the test stand hydraulic fluid. To prevent contamination of future cylinders, the test stand system can be equipped with hydraulic filters to remove the particles from the fluid.

Hydraulic filter manufacturers have developed high-performance filter elements that effectively remove microscopic particles, even down to 1 micron. The best strategy is multiple filters at different locations in the system.

Return Line Filter

Operators should prioritize the return line as the primary filter location. This placement immediately captures hydraulic cylinder contamination flushed from the cylinder and maintains clean fluid in the reservoir. Engineers must always size return filters for the maximum possible return flow. They calculate this flow by multiplying pump flow by the ratio of blind-end area to annulus area. Hydraulic cylinder test stands typically handle cylinders with ratios from 1.1:1 to 10:1. Designers size the return filter according to return flow from the highest-ratio cylinder tested.

Pressure Line Filter

The next location is in the pressure line, generally after the pump and before the directional control valve, to ensure the fluid going into the cylinder being tested is as clean as possible.

Kidney Loop

Ideally, the system will also include a low-pressure offline circuit that operates at a consistent flow rate, independent of the main test stand hydraulic system. These subsystems are designed for the sole purpose of conditioning the fluid. If the fluid becomes contaminated, the kidney loop can filter the fluid to prevent damage to the high-pressure components in the test stand hydraulic system.

Reservoir Breather

This critical piece of the filtration puzzle is often overlooked. Each time a test cylinder is extended, air from the surrounding atmosphere is drawn into the reservoir. Inexpensive, coarse cellulose or foam media will allow a high percentage of particles less than 10 microns to pass, increasing the contamination of the fluid. Select breathers that closely match the fluid filter’s micron rating and replace them regularly to meet your targeted cleanliness levels.

Significance of Cleanliness Standards

Operators should regularly measure and monitor test stand fluid cleanliness. This confirms proper filtration system function. It also removes hydraulic system contamination from each cylinder test. The ISO 4406 standard is most widely accepted. It uses a three-digit format. This format reports particles greater than 4, 6, and 14 microns per volume.

For example, ISO code 17/15/13 shows 640 to 1,300 particles over 4 microns per milliliter. It also indicates 160 to 320 over 6 microns. Additionally, it reveals 40 to 80 over 14 microns. Users apply this format to define fluid cleanliness or specify desired levels. Hydraulic component manufacturers often publish maximum allowable contamination levels. Because tiny unseen particles cause damage, visual fluid examination proves inadequate. Conventional analysis methods include gravimetric, laboratory, and inline particle counters.

• Gravimetric:

  The gravimetric method involves passing a fluid sample through a patch to capture particles, followed by weighing and microscopic examination. This approach remains labor-intensive and typically exhibits a high margin of error.

• Laboratory Analysis:
  Operators collect bottle samples and submit them to laboratories for detailed analysis, which evaluates particle count, viscosity, water content, contamination composition, and other factors. Although results are comprehensive and accurate, delays arise; for instance, a two-day report revealing fluid issues exposes all cylinders tested during that period to contamination risks.

• Inline Particle Counters: [DSC_0111-2]

  An inline particle counter directs a laser through a fluid stream, where sensors detect particle size and quantity, yielding continuous, immediate reports on particle counts and ISO cleanliness codes. This real-time data supports actions such as postponing tests until cleanliness improves, links specific cylinder tests to fluid cleanliness levels for potential warranty claims, and assesses the efficacy of continuous improvement initiatives aimed at enhancing cleanliness.

Reduce Your Risk of Hydraulic Cylinder Contamination

Machine OEMs and End Users should take measures to prevent costly and time-consuming hydraulic failures. In addition to installing and maintaining hydraulic filters, preventing ingression of particles into the system, and excluding moisture, it is also beneficial to consider contamination when selecting a hydraulic cylinder supplier.

Specifically, choose a manufacturer who understands the risk of hydraulic cylinder contamination and has implemented appropriate standards and procedures. These preventive measures should begin when workers cut the first piece of material with a saw. They must continue through all machining and welding processes. The precautions need to carry through until engineers complete functional testing. These precautions demand investment and commitment from the cylinder manufacturer. Likewise, customers should look beyond the cylinder’s initial purchase price. They must consider the far greater value of reducing risks from contamination-related failures.