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Q. How often should hydraulic fluid be changed?
A. Fluid samples should be sent to specialised Fluid Testing Laboratories on a regular basis and renewed on the laboratories recommendations.

Q. What is a major cause of component failures in Hydraulic systems?
A Oil contamination. Independent tests have shown that up to seventy percent of failures in hydraulic systems are caused by contaminated fluid.

Q. Is there a correct way to filter hydraulic fluid?.
A. New fluid must pumped from the drums via a ten micron filter when filling or topping-up reservoirs. Remember, new fluid is not clean enough for hydraulic systems.

Q. Where in a hydraulic system should filters be installed?
A. For the best protection of hydraulic systems, a pressure line filter and a return line filter are required. A pressure line filter must be installed after the pump, while the return line filter is to be installed in the return line, just before it enters the reservoir.

Q. Are the pressure and return line filters enough to protect a system adequately?
A. All reservoirs must be fitted with side filtration systems. This is a filtration unit which is free-standing, circulating the reservoir fluid on a continuous basis. The unit must run twenty-four hours per day.

Q. What is the recommended flow rate for the side filtration pump?
A. Normally 10% of the reservoir capacity in litres/minute (e.g.200 litre reservoir with a 20 litre/minute side filtration pump). If servo or proportional valves are used, the side filtration pump must be at least 20% of the reservoir capacity in litres/minute.

Q. Is there a recommended micron rating for hydraulic filers?
A. Install filters with a micron rating of at least Beta 10 = 100. (10 micron with an efficiency of 99% for one pass). Important, when servo or proportional valves are used, filters with a rating of Beta 3 = 200 must be installed. (3 micron with an efficiency of 99,5% for one pass).

Q. What is the function of a hydraulic pump?
A. Pumps are installed in hydraulic systems to supply flow rate. The flow rate of a pump determines the speed of a cylinder or hydraulic motor. Pumps do not supply pressure. Pressure is caused by a resistance to flow. (If there is no load there is no pressure).

Q. Which is the best way to park earth moving machinery?
A. Always ensure that where possible, piston rods are fully retracted. All exposed rods must be cleaned before starting the days work.

Q. What are the requirements for determining power to drive hydraulic pumps?
A. Power = Pump flowrate x Pressure.
Power = Kilowatts.
Pump Flow Rate =Litres/Minute.
Pressure = MegaPascal.
To overcome hydraulic losses increase the theoretical power by 20% (i.e. x 1,2)
For Simplification. KW = (MPa x l/min x 1,2) / 60

Q. What is the main function of a reservoir?
A. There are a number of functions of a reservoir. Initially to store the hydraulic fluid. It is also where the fluid is serviced before it is pumped back into the system. The reservoir acts as a heat exchanger facilitating cooling of the hydraulic fluid before it is pumped back into the system. In the unlikely event of there being any entrained air in the fluid, a reasonable dwell time for the fluid in the reservoir, will allow air bubbles to rise to the surface and dissipate.

Q. Are there any pertinent design criteria for reservoirs?
A The first choice of material should be Stainless Steel or Aluminium, to eliminate corrosion. The area above the fluid level is not in the lubricated zone, so corrosion will occur if mild steel is used. Size a reservoir two to four times the pump flow rate in litres/minute.

Q. Is there a preferred method in mounting pumps for a hydraulic system?
A If possible, it is best to use a bell-housing to mount the pump to the motor. Mount the pump outside the reservoir, below the fluid level. On occasion pumps have to be replaced, externally mounted pumps facilitate simple and fast replacement. If the pumps are mounted internally in the reservoir, pump replacement becomes very time consuming and difficult for the maintenance personnel to work over the hydraulic fluid. A further problem is that the large opening will allow dust and debris to fall into the fluid.