Manufacturing of hydraulic, pneumatic units &
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Contamination / aeration of hydraulic fluid


Contamination affects all types of hydraulic equipment. The precision parts to high tolerances are susceptible to the effects of contamination. A dirty fluid causes wear, which accelerates the leakage and the development of the heating system. The heat reduces the lubricity of a fluid and cause more wear.

If a hydraulic pump or motor is defective, the system becomes contaminated. Remove the unit for repair disorder. The tank should be drained, washed and cleaned. An inspection of hoses, pipes, cylinders and valves should be made for wear and the presence of particles from the unit disorder.

Replace filter elements. Have fluid removed from the system and fill the tank with new hydraulic fluid clean. Install a new unit or refurbished and start the system. Let the system work for a period of time to verify the normal operation of the system. The filter elements should be replaced after 40 to 50 hours of operation. This ensures that the system is essentially clean and free of all residues of the defective unit.


The contamination of a system can result from various factors:

  • Inadequate Design

    • Tanks can be cleaned.
    • Vent cap with inadequate filtration, which lets the contaminants in the air.
    • Design of seals cylinder inadequate (no scraper rod).
    • Material rod with low wear characteristics.
    • Circuitry incorrect (anti-cavitation valves failed in some circuits).
    • Inadequate filtration.
  • System Maintenance weak or missing

    • Contamination during oil filling.
    • Event tank defective or inadequate.
    • Rod and cylinder damaged or defective seals.
    • Changes of hydraulic parts made in conditions of filth.
    • Change filter elements not met.
    • Cleaning the hydraulic system is not after a broken pump.

A surgical cleanliness is essential. However, the common practice of cleanliness during assembly of the system will become profitable by increasing the useful life of equipment.

An excessive and inappropriate use of sealant on threaded pipes and gaskets can cause breakage of pumps, especially if a hardening sealant is used.

Another source of possible contamination: pipes and fittings received from suppliers without plugs to block the openings, which allows access to all kinds of particles.

  • Inadequate operating conditions (dust, humidity, rain ...)

From experience, it has been proven that the machines used in a very dusty and high airflow require more robust components. Piston rod chrome plated and changing filter cartridges are required more frequent.

Aeration (air bubbles in the fluid)

Aeration can be of several forms: large bubbles, foam at different levels of suspension. This is usually the cause of a noisy pump. The bubbles cause extremely rapid wear of the "ring" wear and corresponding valves.

This wear develops undulations in the "ring" and there will be a frosted appearance. In cases of extreme ventilation, wear is so fast that the "ring" and the valves can be destroyed in one hour.

Aeration can also cause incorrect functioning in some circuits sensitive to this problem.

  • Possible causes and remedies:

    • Leaks in the inlet of the pump
      • The nipples may be porous. Use an approved sealant on all threads of the conduit.
      • If the surface of the inlet of the pump is rough, broken or mutilated, air can penetrate through the seal ring O-ring ".

With either of these defects, air can be admitted in the hydraulic system.

    • Leakage by O-rings O-ring "

O-rings are used to seal the entrances / exits in many control valves. These joints can be verified by applying grease around the part to check. If the noise stops, the problem was localized and can be repaired.

On systems that are operated at excessive temperatures, the O-rings can harden, allowing air to enter the system. This is true not only in the pump, but also in other parts of the system.

Another factor accentuating the admission of air into the system, the composition of the fluid. The fluids that contain lots of sulfur tend to accelerate the hardening of the O-rings. This is one of the main reasons for keeping a good operating temperature.

The normal operating temperature of the system is 110-120 deg F. When the operating temperature exceeds this value, problems can occur. The operating temperature of a system should be measured at the outlet of the pump. Every 5 degrees above 150 degrees F to 200 hours decreases the life of the hydraulic fluid.

    • Leakage through the seal of the pump shaft

Most pumps valves are internally drained. The cavity of the sealing of the shaft is connected to the pump inlet. Voids Excessive intake can cause the penetration of air through the seal of the tree. The vacuum measured at the maximum pump inlet should not exceed 5 inches of mercury.

A misalignment of the shaft can increase the intake of air beyond the seal of the tree. The couplings to universal joints or grooves can cause the intake air through the seal when not perfectly aligned. The direct couplings should never be used.

The use of inappropriate tools can maim and distortionner seals at the facility. The outer diameter of the tree should be lightly polished before installation to remove the burrs and roughness to the place where you installed the seal.

For a given application, the material forming the seal must be appropriate. A material that is not compatible with the fluid system can deteriorate and cause leakage problems.

    • Leak seals rod caused by a cylinder cavitating

On applications with rapid cycling (eg up / down), air can enter the system through the seal of the cylinder rod. Voids in excess of 20 inches of mercury have been recorded in systems without a "check valves" anti-cavitation. This is sufficient to force the particles of dust and air to pass through the seal and the stem into the system.

A "check valve" anti-cavitation will flow from the tank into the region of the cylinder rod in a vacuum condition. The "check valves" anti-cavitation should always be used to prevent a condition of high vacuum to develop. This will reduce the possibility of contamination of the fluid by the seal of the cylinder rod in action.

    • Turbulence in the tank

When not properly located, the return lines can cause turbulence and aeration in the tank. A plexiglass window should be placed on the tank to study the flow conditions. Return lines that discharge above the level of fluid favor the formation of bubbles in the system. The lines should always be completed below the fluid level. The container must be deep enough to prevent aeration.

    • Swirling fluid in the reservoir

If the fluid level in the reservoir is low and demand for admission is high, swirl (vortex) can develop, which has the effect of admitting air into the pump inlet. In a hydraulic system, turbulence is usually the result of a fluid level too low or inadequate design of the tank.

One of the best ways to address the problem is to place an anti-cavitation plate above the tank outlet. This is a simple plate of sheet metal of at least 1 / 8 "thick, just above the opening of the tank outlet. This plaque will flow horizontally and actually enhance and expand tank opening. This prevents the development of turbulence.

    • Release of trapped air in the fluid insufficient

There is a considerable amount of air suspended in the fluid cold. The fluid warming, air is released into the system. Similarly, a reduction of fluid pressure releasing trapped air.

A simple valve billowing "poppet" may create an opening which will increase velocity and decrease its pressure. With the pressure reduced, releasing the air in the system. The return of this type of valve should be below the level of the fluid reservoir and as far as possible to the exit. This gives enough time to air released by the valve billowing to be eliminated before entering the exit area of the tank to be subsequently admitted to the pump. In some cases, a special line of return, or valves are bled of air used to remove air from the system.

A deflector 60 is special "mesh" can be installed in the tank. The deflector should be positioned at an angle of 30 degrees in the tank so that oil entering the tank is above the deflector, while the oil that comes out is below the deflector. The screen should be below the fluid level, deep enough to prevent the foam surface to come into contact with the deflector. The foam surface may infiltrate and reach the exit region of the tank.

The deflector screen when properly designed and installed, remove the fluid in all the bubbles of medium and large.


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