Commonly used on all Full Power Braking Systems. These are systems where braking pressure is not taken directly from operator input forces, and so tend to apply mostly in large mobile applications, such as –
Also used to charge auxiliary control functions such as Emergency Steer functions
So what do we want from the charging circuit?
•Reliable Unload / ReloadPerformance
•Long time between recharges
•Adjustability of unload and reload settings to suit machine
•Compliance with Pressure EquipmentDirective
•Quiet and vibration free
•Ability to combine accumulator charging system with other functions
•Ability to install in limited or difficult space claims
•Use with either fixed displacement or variable displacement pumps
•No need for solenoid valves or control electronics
Why use an Unloader circuit?
In below schematic clamp cylinder extends and pump unloads across relief valve. Where a pump system unloads across a relief valve the negatives are:
• Power Consumption
• Component Wear
OEM’s in Europe will be referring to BS EN ISO 3450 which specifies the braking system requirements for Earthmoving machinery.
This is what effectively dictates the volume of stored energy required on a particular machine. The standard demands that after 5 operations of the brake pedal the secondary brake performance must not be compromised.
TypicalArticulated Dump Truck has nearly 12 litres of Accumulator Capacity for theBrake System !
One point worth mentioning about accumulators is that piston accumulators are recommended for brake and steer functions. The failure modes for piston accumulators tend to be progressive rather than sudden.
Remember where there is an accumulator in the system the European PRESSURE EQUIPMENT DIRECTIVE will apply !
From29 May 2002 the pressure equipment directive will be obligatory throughout theEuropean Union.
Under the Community regime of the Directive, pressure equipment and assemblies above specified pressure and/or volume thresholds must:
•meet essential safety requirements covering design, manufacture and testing;
•satisfy appropriate conformity assessment procedures; and
•carry the CE marking and other information.
Pressure equipment and assemblies below the specified pressure / volume thresholds must:
•be designed and manufactured according to sound engineering practice; and
•bear specified markings (but not the CE marking).
Taken from http://ped.eurodyn.com