Diagnostic Hints:
- Hydraulic systems do not normally fail overnight. There are usually symptoms of
an approaching problem. If the “Suggested Remedies” do not correct the trouble and you need to refer to Oiltech’s hydraulic specialists, always give as much
background to the trouble as possible.
- Get to know the operation of the equipment you’re maintaining. Read manufacturers’
instructions and study circuit diagrams carefully, particularly recommended start-up procedures.
- Use the right tools – some hydraulic components are delicate and it can take just
the right touch to make them tick.
- Don’t take shortcuts – it rarely works
- Play it safe. Most modern hydraulic equipment works in the range of 1 Mpa to over 100 Mpa (150 – 15000 psi) and high pressures can be dangerous. The safest way to work on any machine is to shut it down first.
- Analyse the system and develop a logical sequence for setting valves, mechanical stops, interlocks and electrical controls.
- Don’t experiment unless it’s your last resort. Manufacturers spend experienced time designing, building and testing equipment. Take it easy when making any improvements.
CONTENTS:
- Excessive Noise
- Overheating
- Incorrect Flow
- Incorrect Pressure
- Erratic Action
- Leakage Around Pump
Excessive Noise
| Symptoms | Remedy |
| Air in fluid | Be sure the fluid reservoir is filled to normal level and that fluid intake is below surface of the fluid. (With rare exception, all return
lines should be below fluid level in the reservoir.) Check pump packing, pipe and tubing connections, and all other points where air
might leak into system. One way to check a point on the intake side suspected of leakage is to pour hydraulic fluid over it. If the pump noise stops, you’ve found the leak. |
| Cavitation | Check for clogged or restricted intake line, plugged air vent in reservoir. Check and wash strainers in a fluid compatible with system fluid and check that the fluid viscosity is not too high. Check for undersized suction line. check proper pump drive motor speed plus pulley and gear sizes, particularly if a replacement motor has been installed. |
| Pump Misaligned with motor | Align unit and check condition of seals, bearings and coupling. Misalignment may be caused by temperature distortion. |
| Loose or Worn; Pump, Motor, Poppet and Seat | Check manufacturer’s maintenance instructions first. Tightening every nut in sight may not be the way to stop noise or leakage. Look for worn gaskets and packings; there is usually no way to compensate for wear in a part and it is almost always better to replace it. Check the fluid specification and quality. |
| Stuck Vanes, Valves, Pistons etc. | Parts may be stuck by metallic chips, bits of lint, etc which need
to be cleaned out thoroughly. Avoid the use of emery cloth or steel hammers etc on machined surfaces. Products of fluid deterioration such as gums, sludges, varnished, and lacquers need to be cleaned from parts with a solvent then dried thoroughly before reassembling. Be sure new replacement fluid in system provides adequate protection against corrosion and has sufficient resistance to deterioration. |
| Filter or Strainer dirty | Filter and strainers must be kept clean enough to permit adequate
flow. Ensure that original filter has not been replaced by one of smaller capacity or inferior quality. Refill with fluid of quality high enough to prevent rapid sludge formation. |
| Valve Setting too Low or too Close to another Valve Setting | If the relief valve sounds noisy, check the pressure setting by installing a pressure gauge and adjust to the correct pressure if necessary. |
Overheating
| Symptoms | Remedy |
| Fluid Overheating | Make sure the fluid supply is up to the correct level so that sufficient
fluid is available to disperse heat in the system. Make sure the fluid in the system is not contaminated. Check fluid recommendations and viscosity requirements; if in doubt it may be worth your while to drain the system, change the filter and refill with the correct fluid. Unusually high temperature conditions may cause fluid of correct viscosity for “working temperature” to thicken too much because of oxidation. A possible cure would be to use a fluid of a higher viscosity index. |
| Internal Leakage too high | Check for wear and loose packing. Fluid viscosity may be too low. Check recommendations. Proceed with caution if you a tempted to try a high viscosity fluid. |
| Relief or Unloading Valve Set too High | Install pressure gauge and adjust to correct pressure. At least
860 Kpa (125psi) difference between valve settings should be kept on most systems, check with
manufacturer’s recommendation. Check that the relief valve is not stuck open. This indicates the system contains dirty or deteriorated fluid. |
| Poorly Fitted or Worn Parts | Poorly fitted parts may cause undue friction. Look for signs of excessive friction; be sure all parts are aligned correctly. |
| Oil Cooler Clogged | On any machine equipped with an oil cooler, it is probable that high
temperatures are anticipated. If temperatures run high normally, they’ll go even higher if oil cooler passages are clogged. If you find a clogged cooler, try blowing it out with compressed air. If this does not work, try solvent or Oiltech Transclean 801. It may be necessary to replace cooler control valve and/or cooler. |
Incorrect Flow
| Symptom | Remedy |
| Pump Shaft Turning in Wrong Direction | Shut down immediately. Some types of pumps can turn in either direction without causing damage; others are designed to turn in one direction only. Check belts, pulleys, gears and motor connections. Reversed leads on 3-phase motors are a common cause of wrong rotation. It may be necessary to replace pilot pressure pump. |
| Pump Not Receiving Fluid | Replace dirty filters, clean clogged inlet line, clean reservoir breather vent and fill the reservoir to the correct level. Overhaul or Replace supercharge pump. Check the yoke activating device is Operative (variable displacement pumps). |
| Mechanical Trouble (broken shaft, drive motor not operating, loose coupling etc.) | Mechanical trouble is often accompanied by a noise that you can locate very easily. If you find it necessary to disassemble, follow the manufacturer’s recommendations to the letter. Improperly assembled pumps are often the cause of no flow. |
| Pump Shaft Speed Too Low | Some pumps will deliver hydraulic fluid over a wide range of speeds, others must turn at recommended speed to give appreciable flow. Find out the speed recommended by the manufacturer, then check the speed of pump with a flow counter if possible. If the speed is too low, look for trouble with driving motor and check relief or unloading valve. |
| Excessive Flow | Check that the Yoke actuating device is operative (variable
displacement pumps). The flow control may be set too high or an improper size replacement pump has been used. |
| Air Leak in System | If any air at all id going through the pump, it will probably be quite noisy. |
Incorrect Pressure
| Symptom | Remedy |
| Pressure Reducing Unloading, or Relief Valve Setting Incorrect | If valve settings are too low, fluid may flow from pump through
valves and back to the fluid reservoir without reaching point of use. If valves are set too high, refer to OVERHEATING advice.
Check that valves are not damaged, worn or dirty. To check relief valve setting, block discharge line beyond relief valve and check line pressure with pressure gauge. |
| Incorrect Control Valve Setting, Fluid “Short Circuit” to Reservoir | If open – centre directional control valves are unintentionally set at neutral, fluid will return to reservoir without meeting any appreciable resistance and very little pressure will be developed. Scored control valve pistons and cylinders can cause this trouble Replace worn parts. |
| Leak in System | Check whole system for leaks. Serious leaks in the open are easy to detect, but leaks often occur in concealed piping. One routine in leak testing is to install pressure gauge in discharge line near pump and then block off circuit progressively. When gauge pressure drops with gauge installed at a given point, leak is between this point and check point just before it. |
| Broken, Worn or Stuck Pump Parts | Install pressure gauge and block system just beyond relief valve. If no appreciable pressure is developed and relief valve is OK, look for mechanical trouble in pump. |
| Accumulator Defective or Lost Charge | Check gas valve for leaks. Charge to correct pressure. Overhaul if defective. |
Erratic Action
| Symptom | Remedy |
| Valve Pistons etc. Sticking | First check suspected part for mechanical deficiencies such as misalignment of a shaft, worn bearings etc. Then look for signs of dirt, sludge, varnished and lacquers caused by fluid deterioration. You can make up for mechanical deficiencies by replacing worn parts, but remember deficiencies are often caused by the fluid level being too low or the use of the wrong fluid. |
| Lack of Mechanical Lubrication | This can cause noisy as well as erratic movement. To avoid wear ensure linkages and machine ways are correctly lubricated. |
| Malfunctioning Servo Amplifier, Servo Valve or Feedback Transducer | Clean and adjust or replace. Check the condition of system fluid and filters. |
| Sluggishness when a Machine is first Started | Sluggishness is often caused by fluid that is too thick at starting
temperatures. If you can accept this for a few minutes, fluid may thin out enough to give satisfactory operation. If fluid does not thin out, or if ambient temperature remains relatively low, you may have to change to fluid of lower pour point, lighter viscosity and/or higher VI. Under severe conditions immersion heaters are sometimes used to pre-heat oil. |
Leakage Around Pump
| Symptom | Remedy |
| Worn Packing | Tighten packing gland or replace packing. Trouble may be caused by abrasives in fluid. A check of points where abrasives might enter should be made. |
| Head of Fluid on Suction Line | Usually it is better to have slight pressure on the suction side of the
pump, although it may not be necessary. With more than slight head, leakage may result. If head is not required and components can be re-arranged, do so. Leakages should always be fixed because they are points which allow suction of air. |