Mobile Hydraulic Applications
Oil Coolers, Air Coolers, Plate Coolers, Oil to Air Heat Exchangers and Oil to Water Heat Exchangers, Butterfly Valves, Butterfly Flanges, Hydraulic Couplings.
For Mobile and Industrial Applications
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The Use of Oil / Air Coolers ( Oil Coolers, Air Coolers, Plate Coolers) in Mobile Hydraulic Applications
1. General : Why do we need hydraulic oil coolers?
Tests show that exceeding the maximum temperature of hydraulic oil reduces its performance and useful life. Additionally high oil temperatures reduce the viscosity of the oil, which leads to increased leakage and increased temperatures. High oil temperatures also result in hardening seals and increased wear on hydraulic components.For example:
An oil temperature increase from 60ƒC to 70ƒC (18 degrees F) reduces the life of the oil by half.
As the oil is overheated it loses its lubricating properties and increases friction and wear on hydraulic components. The result is increased heat and increased wear on hydraulic components. Hydraulic components are constructed with very close tolerances, high heat and loss of lubrication can result in severe damage or seizure.
The following damage may occur:
• Seizing of pumps, motors and valves
• Hardening of seals
• Damage from friction on cylinder tubes, piston rods and valves
• Damage to valve seats, etc
Why are oil air coolers (hydraulic oil coolers, air coolers, oil coolers, plate coolers) used in mobile hydraulic applications?
The temperature of available water makes it necessary to use air to cool the hydraulic oil to a desirable temperature. In mobile hydraulic applications there are three options for driving the cooling fan. DC electric (12v or 24V), hydraulic or mechanic power.
2. Calculation of the heat dissipation:
The calculation is the same for all (mobile & industrial) applications, it depends on the type of system and the components in the system.
Efficiency of particular systems:
• Gear pump power station and fixed pump systems: 0.7
Following points should be taken into consideration:
• Variable pump systems: 0.8
• Hydrostatic drives: 0.8
• Piston hydrostates: 0.85
• Open circuits with piston components: 0.8
• Orbit motor systems (Gerotormotor):0.8
• Type of equipment: which units are operated via hydraulics? (motor drives, cylinder systems, combination of both)
• Period of use (service factor)
• Location (dust laden air, other environmental influences, elevation)
To get the right cooler (hydraulic oil cooler, air coolers, oil coolers, plate coolers) size you have to pay attention to:
Oil flow :
Generally the oil flow is known and it is necessary for the calculation. But sometimes there are some requirements, where the oil flow can change considerably. For example, a hydraulic crane: The power of the pump is known. The movement of cylinders causes a momentary high flow in the return line. This pulsation has no great effect on the heat dissipation, but we need to make sure the oil can flow through the cooler element without damage to the element. The increased flow will result in a higher flow resistance in the return line. This fact is very critical in systems that are used in cold climates or if the oil has a high viscosity when it is started. You can avoid damage by using a bigger element or by the use of a bypass valve.
Oil Temperature :
Usually in mobile hydraulics the oil temperature should not exceed 60ƒC (mineral oil and synthetic oil). Using biologic oil, the temperature should not exceed 50ƒC. Exceeded these temperatures can result in loss of lubrication and gum.
Cooling circuits :
The most commonly used cooling circuit is the return line circuit. Here it is important that there are no pressure spikes or shocks, which could damage the element. Such pressure spikes may be caused by control valves, sequence valves and relief valves. Because such pressure spikes only last for a interval of a few milliseconds they cannot be detected by standard instruments, the use of special electronic instruments is necessary. Bypass valves are of little help with these high-pressure spikes.
The only way to avoid these pressure spikes is by using an accumulator, or by using a separate return line for those components that cause the pressure spikes (in most cases this is not possible or not cost effective). The easier solution is the installation of a separate cooling circuit.
The above mentioned return line cooling is used in open circuits. In hydrostatic drives (closed circuits) normally the charge circuit or the flushing circuits are used as a cooling circuit. As mentioned in the paragraph on oil flow, there are pulsations in some machines (the oil-flow through the cooler changes quickly). In contrast to pressure spikes, a larger element or the installation of a bypass valve can solve the problem of pulsations.
3. DC Fans
Generally, power supplied to the fans should be done through a relay. Additionally, check that the alternator is sufficient to supply the fan, otherwise the battery of the vehicle will be drained when using the fan. Use a main electrical switch which will turn off all electrical power when the machine is not in use. Without a main switch it is possible that the thermostat could activate the cooling fan because of warm oil. If the machine is not running there will be no oil flow through the cooler and no cooling, except convection. The fan will run for hours and drain the battery.
4. Use of electronic components:
Some applications are in use with electronic components, which are supplied with DC power, this may cause problems when the cooling fan is started. The operation of the oil cooler is not effected by these problems, but we need to be aware of them if a customer asks.
The starting current (in rush) is 3 times the normal current for a typical cooling fan. If there is a weak battery or generator a high decrease in voltage will occur. This decrease could damage or disrupt some electronic components. Additionally, the surrounding wires will produce a magnetic field via induction and a voltage spike. This impulse is taking the shortest way to ground and may damage electronic components. A good solution is to install the cables separate from the vehicle system and go directly to the main power switch. The use of shielded cables is also recommended.
5. Recommendations for using oil/air coolers in mobile applications:
Mounting of the oil cooler ( hydraulic oil coolers, air coolers, plate coolers, oil coolers) is much more critical in mobile applications than it is in industrial applications. Factors such as vibration, shock, space available, access to clean cooling air and protection from damage all must be considered when mounting the cooler in mobile applications.
Vibration from the motor and road are an important factor in mobile equipment. To avoid damage from vibration it is necessary to shock mount oil coolers. This is done using isolation blocks; these blocks consist of rubber or combinations of rubber and steel. This flexible mounting requires all connections also be flexible so the cooler is free to move and the connections are not stressed.
The cooler ( hydraulic oil coolers, air coolers, oil coolers, plate coolers) can be protected from damage by stones or other objects by using a protective housing and a core guard available from ASA.
Location is an important factor in mounting the cooler ( hydraulic oil coolers, air coolers, oil coolers, plate coolers). Place the cooler ( hydraulic oil coolers, air coolers, oil coolers, plate coolers) where it is protected against damage, but remember it is necessary that the cooling air can flow unrestricted. Without clean, cool air the heat dissipation by the cooler ( hydraulic oil coolers, air coolers, oil coolers, plate coolers) will decrease significantly. The distance on each side of the cooler ( hydraulic oil coolers, air coolers, oil coolers, plate coolers) should be half the element width (minimum). The same is true for the area behind the cooler ( hydraulic oil coolers, air coolers, oil coolers, plate coolers). Don’t place the hydraulic tank behind the cooler ( hydraulic oil coolers, air coolers, oil coolers, plate coolers), otherwise the warm air from the cooler ( hydraulic oil coolers, air coolers, oil coolers, plate coolers) will be absorbed by the tank, and reduce the heat dissipation. At all times keep the cooler face clean, free of dirt and debris. Anything that reduces the airflow through the cooler will reduce the heat dissipation.
Cleaning of oil/air cooler (hydraulic oil coolers, air coolers, oil coolers, plate coolers) element:
Periodic cleaning of the cooler (hydraulic oil coolers, air coolers, oil coolers, plate coolers) element is recommended. The cleaning methods vary depending on the type of contamination (wet or dry). The simplest way to clean the element is to use compressed air for dust contamination. If contamination is sticky (mixture of oil and dust) we recommended that the cooler be disassembled from the fan unit. The element alone can then be treated a liquid cleaner and flush with water. Then use compressed air for drying and removal of debris. Be careful when using compressed air, high pressure cleaner or steam cleaner. The electric fan or the fins of the element can be damaged by high pressure or steam. The blow direction for air, water or steam must to be opposite the direction of normal airflow to ensure effective cleaning. On vehicles used in corrosive environments (salt) clean the cooler frequently with water to prevent corrosion which can damage the element.