Product category:
Hydraulic Components
News Release from: Parker Hannifin | Subject: Hydraulic accumulators
Edited by the Engineeringtalk Editorial
Team on 30 January 2003
Hydraulic accumulators safeguard
lubrication
In any industrial application requiring pressurised lubrication during powering down there is always the risk of severe damage being caused to equipment if the supply of pressurised oil fails.
In any industrial application requiring pressurised lubrication during powering down, or freewheeling to a stop (such as turbochargers, turbines, hydraulically-driven flywheels, swing drives, hydrostatic bearings etc), there is always the risk of severe damage being caused to equipment if the supply of pressurised oil fails The use of an hydraulic accumulator alleviates these dangers by storing lubrication fluid under pressure during normal running and releasing the oil during the shut down period
In addition to their widespread use in automotive applications, turbochargers are used extensively on petrol and diesel engines in generator set and large pumping unit applications to increase power output.
These turbochargers are driven off the exhaust of the engines and can spin at speeds in excess of 16,000rev/min.
The exhaust gasses which drives these units can reach temperatures in excess of 500C.
When the engines are shut down, pressurised lubrication from the engine-driven pump is no longer available to the turbocharger, even though the turbine blades continue to spin for several seconds at very high speed.
A supply of pressurised oil during this phase is critical, both for lubrication and for cooling of the turbine bearings, and lack of pressure can damage the turbocharger resulting in premature failure of the unit.
By incorporating a Parker Hannifin hydraulic accumulator into the lubrication circuit, this potential problem can be eliminated.
Parker recommends piston-type accumulators for these applications because of their ability to withstand extremes of temperature, which can vary from -20 to over +50C.
Under these conditions, the compression-type seal of the piston accumulator makes the unit more reliable than a bladder-type accumulator.
The use of an accumulator to provide pressurised lubrication during powering down is also common in applications where hydrostatic bearings are used.
In these applications, if power is lost, it can take several minutes for, say, a large turbine in a power generation plant to come to a stop.
Without proper lubrication, the hydrostatic bearings can freeze up causing millions of pounds in repair costs and long periods of downtime.
On turbocharger applications, the size of the accumulator will depend on how many turbochargers are used on the engines, and the size of the units.
In a typical automotive application, a two litre accumulator is sufficient to supply the fluid to one turbocharger.
Precharge pressure in the accumulator is usually about 1.4bar and the oil pressure is generally 4.0 to 4.5bar.
This results in approximately 0.5 litres of fluid being delivered at a pressure of between 2.0 and 4.0bar.
There is about one litre of fluid stored in the accumulator between the operating pressure of 4bar and the precharge pressure of 1.4bar.
On large hydrostatic bearing applications, the size of the accumulator is determined by the number of bearings be to be lubricated and the time required for the unit to come to a stop.
Accumulators in these applications can range from under 20 litres to over 400 litres in size, with pressures in these units tending to be much higher than in automotive-type applications. Request a free brochure from Parker Hannifin ...
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