A Publication of Hydraulic Training Associates

System Cleanliness is

Primary A GUIDE TO A HEALTHER HYDRAULIC SYSTEM

TABLE OF CONTENTS

1. INTRODUCTION

2. FLUIDS

3. FILTERS

4. RESERVOIR

5. LINES AND FITTINGS

6. HEAT EXCHANGER

7. CONTOLS

8. SEAL LEAKS

9. OIL SAMPLES

10. CONCLUSION

System Cleanliness

INTRODUCTION

System cleanliness if Primary

Cleanliness is the primary means of ensuring satisfactory hydraulic systems life. The oil and all parts of the system must be kept in a very clean condition at all times. There are a number of preventative maintenance procedures that help eliminate many potential problems. These procedures must be performed on a regular basis. Failure to perform the preventive maintenance work can result in the system’s components to be damaged or fail.

With pumps and valves designed to closer tolerances and finer finishes, fluid systems operate at ever increasing pressures and efficiencies. These components will perform as designed as long as the fluid is clean. Oil cleanliness results in increased system reliability and reduced maintenance. As particles are induced or ingressed into a hydraulic system, they are often ground into thousands of fine particles. These tiny particles are tightly packed between valve spools and their bores, causing the valve to stick. This is known as silting.

To prevent silting, early component wear, and eventual system failure, engineered filtration is required. Engineered filtration includes understanding the required micron rating, application of the beta ratio, maintaining proper ISO code cleanliness levels, and filter location specific to the system design and environment.

Fluids How often should I change it?

In a sealed reservoir system, changing the hydraulic fluid every 2000 hours of operation is generally adequate. A more frequent fluid change will be required if the oil has become contaminated by water (indicated by a milky appearance) or by other foreign materials: or if it has been subjected to abnormal operating conditions, such as excessive temperature. In an open reservoir system that uses an air breather filler cap, the hydraulic fluid should be changed after approximately 500 hours of operation. When changing the oil, always clean and flush the reservoir before refilling and use only clean, pre-filtered fluid. Be sure to consult your maintenance manual for the proper fluid to be used based upon manufacture specifications.

Micron is the designation used to describe particles sizes or clearances in hydraulic components. A micron is equal to 39 millionths of an inch. To put this into perspective the smallest dot that can be seen by the naked eye is 40 micron.

Filtration devices are used to filter particles out of the system’s fluid. A filter’s efficiency is rated with a beta ratio. The beta ratio is the number of particles up stream from the filter that are larger than the filter’s micron rating divided by the number of particles downstream larger than the filter’s micron rating.

To specify the cleanliness level of a given volume of fluid we refer to what is known as an ISO code, or ISO solid contamination code. This code, which applies to all types of fluid, provides a universal expression of relative cleanliness between suppliers and users of hydraulic fluid.

With a sealed reservoir system, a good rule of thumb is to check and change the 10 micron filter that is used every 1500 hours of operation. With an open reservoir system, the filter is be changed every 500 hours in conjunction with the oil change. The O-rings and gaskets used on the filter assembly are to be changed each time the filter element is replaced.

Micron, Beta Ratio, ISO?

Filters

The hydraulic reservoir should be checked daily for proper fluid level and for the presence of water or metal particles in the fluid. Before opening reservoir, be sure that any dirt around the filer cap has been removed. Also, the transfer pump and container used to add fluid to the reservoir must be very clean.

In addition to holding the system’s fluid supply, the reservoir serves other important functions. It cools the hydraulic fluid. This is accomplished by dissipating excess heat through its walls. It conditions the fluid. As oil waits to leave the reservoir solid contaminates settle out while air rises and escapes.

A well designed hydraulic system always includes a properly designed reservoir. A reservoir used for mobile applications should include the following components one or more baffle plates to prevent retuning fluid form entering the pump inlet and to prevent the fluid from sloshing around as the equipment moves, a clean out cover, a sealed fill tube, a breather/filler that will clean and dry air entering the reservoir as the reservoir breathes, a sight gauge and temperature sensor, a magnetic drain plug at the lowest pint in the reservoir, and fluid lines terminating below the fluid level.

Reservoirs for mobile equipment are usually minimal in size, only holding enough fluid to meet the needs of the system. Less fluid means the fluid is circulated more often, giving less time for heat to dissipate; solid contaminates to settle out, and air to escape. A heat exchanger often becomes necessary to keep the fluid cool.

Am I too small?

Reservoir

Hydraulic lines and fittings should be inspected daily for wear, damage, or any fluid leakage. Tighten, repair, or replace each fitting or line that is found to be defective. Also, check the pump inlet hose, if used, to be sure that the inner liner has not collapsed causing damage inlet pressure conditions for the pump.

Transmitting power from one location to another is a key element in a system design and performance. This transmitting of power is known as fluid conducting. Fluid conductors describe different types of conducting lines that carry hydraulic fluid between components.

The three principal types of plumbing materials used in hydraulic systems are steel pump, steel tubing, and flexible hose. A safety factor of 4 to 1 is recommended on the pressure rating of the plumbing material. To determine the working pressure of the conductor, the rated burst pressure is divided by a safety factor of four.

• Hoses can last a long time, but all rubber slowly deteriorates with contact from various substances, such as solvents, water, sunlight, and heat. Hoses are not a permanent as metal conductors and should be replaced every few years.

• Proper hose installation is critical. Improper bending twisting, or lack of proper anchoring may lead to hose failure.

Size matters?

Lines and Fittings

Core and cooling fins of the heat exchanger must be kept clean at all time in order to maximize cooling and system operating efficiency. The unit should be inspected daily for any external blockage or dirt accumulation and cleaned, if necessary. Utilizing a fin comb to straighten the fins will enhance the coolers ability to condition the oil properly. If the fins are not straightened the cooler will not produce the required cooling and compromises the systems life.

Temperature control is critical in hydraulic systems. Even with the best circuit design, there are always power losses in converting mechanical energy into fluid power. Heat is generated when ever fluid flows from high to low pressure without producing mechanical work. Heat exchangers may be required when operating temperatures are critical or when the system cannot dissipate all the heat that is generated.

There are two basic types of heat exchangers. Each is based on a different cooling medium: water cooled heat exchangers and air-cooled heat exchangers. If cooling water is available, a shell and tube heat exchanger may be preferred. Cooling water is circulated through a bundle of bronze tubes from one end cap to the other. Hydraulic fluid is circulated through the unit and around the tubes containing the water. The heat is removed from the hydraulic fluid by the water.

Air-cooled heat exchangers consist of a steel radiator core through which fluid flows while a strong blast of air passes across the come. In industrial applications the air is pushed by an electric motor driven fan.

Air or Water?

Heat Exchanger

Inspect, adjust, lubricate, and lock the control cable and linkages in place as required. These items can be quickly looked at during the other daily inspection of the transmission to determine whether any problems are visible. Normal operations of systems can vibrate and jar which may take controls out of adjustment or loosen linkages. Lubricating the pins, locks and cables where possible helps to insure the functionality of these components.

Is there a hang up?

Controls

Shaft seals, housing gaskets, and so on used on the pump and motor should be checked daily for any leakage. If any seepage or leakage is noticed, plan should be to replace the seal. This generally will require that the component to be removed from the system in order gain the accessibility to disassemble the unit.

Seals that are allowed to continue leaking will allow dirt to be ingressed into a system. Damage will occur as the system is allowed to be compromised thus costing time and money as you replace the components.

A simple inspection of the systems in operation as well as in down time will help to reduce the down time if inspected properly.

Drips can be damaging

Seal Leaks

Regular oil sampling can produce a good record of how the system if operating. The oil sample will also indicate failures which are about to happen and allow for replacement or repair of damaged components before catastrophic failure occurs. Oil samples should be conducted every time filters are replaced.

Below are four examples of oil samples taken on four identical systems, the first sample indicates a failure taking place and the third shows that a problem is starting to happen.

Do you see what I see?

Oil Samples

1 2

Oil Samples

Do you see what I see?

Being able to read an oil sample will give advanced notice of repairs that need to be made before extensive damage take place, thus saving component cost and down time.

3 4

Understanding Hydraulics and Schematic Troubleshooting: This e-book is just a small sample of what is discussed in our two day seminars.

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