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A Hydro-pneumatic accumulator consists of a twin chambered cylinder which is separated by a floating piston. One chamber is connected to the hydraulic line, and contains the hydraulic fluid. The other chamber contains nitrogen which is held under pressure

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Introduction

1. Functional Description 1.1 Hydraulic Accumulator. A Hydro-pneumatic accumulator consists of a twin chambered cylinder which is separated by a floating piston. One chamber is connected to the hydraulic line, and contains the hydraulic fluid. The other chamber contains nitrogen which is held under pressure thus providing the compressive force on the hydraulic fluid. The hydro-pneumatic accumulator uses an inert gas such as nitrogen to eliminate the risk of an air-oil vapour explosion. 1.1.1 Primary Function Hydraulic accumulators store hydraulic energy to be provided back to the hydraulic system when necessary. The accumulator stores energy when the hydraulic system pressure is greater than the accumulator and provides hydraulic energy when the accumulator pressure is greater than the system pressure. 1.1.2 Secondary Function The accumulator is designed to hold high pressures without the input of energy from the pump. This prolongs the operational life of the pump as less demand is placed upon it. Furthermore, the hydraulic accumulator allows the supply circuit to respond more efficiently to changes in demand. The accumulator is situated in close proximity to the hydraulic pump in line with a non-return valve. This prevents back flow of oil to the pump. 1.1.2 Protective Function The hydraulic accumulator reduces the demand on the hydraulic pump, thus deleting the need for an otherwise larger pump to cope with the extremes of demand. The accumulator also has the added benefit of absorbing pulsations of energy emitted from the hydraulic pump, thus preventing damage to the circuit from the effects of fluid hammer; particularly to the hydraulic lines. ...read more.

Middle

Together with the non-return valve, the secondary function of the hydraulic gear pump is to prevent the backflow of hydraulic fluid from the hydraulic accumulator; an event which will reduce the efficiency of the hydraulic system. HAZOP 1. Pump oil from the tank to the accumulator a) Functional failure: pump will not pump oil * Suction and/or discharge valve close or clogged * Excessive air entrapped in hydraulic fluid * Speed (RPM) too low * Reservoir low or empty * Electrical failure, pump wiring faulty b) Functional failure: Pump does not deliver sufficient capacity * System relief valve set too low or leaking * Oil viscosity too low * Excessive air entrapped in hydraulic fluid * Speed (RPM) too low * Broken impeller or bent vanes * Instruments give erroneous readings c) Functional failure: Pump delivers flow intermittently * Excessive air entrapped in hydraulic fluid * Hydraulic fluid leak in line d) Functional failure: bearing run hot and/or fail on a regular basis * Broken impeller or bent vanes * Inadequate lubrication * Lubricant contamination * Bearing failure Function Function Failure Cause (Failure Mode) Consequence Frequency Severity Safety Enviro Losses/DT Repair Cost Recommended Actions Detectability RPN Type Pump oil from the tank to the accumulator Pump will not pump oil Suction and/or discharge valve closed or clogged Equipment detention, reduced performance of actuator arm requiring maintenance intervention 2 5 1 1 5 3 Operator/maintenance checklist. Check system valves for proper setting 5 50 Hydraulic Excessive air entrapped in hydraulic fluid Equipment detention, reduced performance of actuator arm requiring maintenance intervention 2 6 1 1 6 3 Root cause analysis. ...read more.

Conclusion

The hydraulic reservoir is also designed to act as a heat accumulator to compensate for losses in the system when subjected to peak power. 1.3.3 Protective Function The reservoir has the added benefit of assisting the hydraulic fluid filter in the process of separating dirt and other particle contaminants from the oil. This is achieved through the general nature of the contaminants settling to the bottom of the tank. HAZOP 1. To store oil in the hydraulic oil tank a) Functional failure: stores no oil * Tank broken or punctured b) Functional failure: stores less than required quantity of oil * Tank broken or punctured FMECA Function Function Failure Cause (Failure Mode) Consequence Frequency Severity Safety Enviro Losses/DT Repair Cost Recommended Actions Detectability RPN Type To store oil in the hydraulic oil tank Stores no oil Tank broken or punctured Equipment detention, hydraulic system fails to operate, requiring maintenance intervention 1 6 2 1 6 5 Operator/maintenance checklist. Ensure tank is in good operating condition. 2 12 Maint. Stores less than required quantity of oil Tank broken or punctured Lowered efficiency and performance of hydraulic system due to lowered hydraulic pressure, necessitating equipment detention requiring maintenance intervention 1 6 2 1 6 5 Operator/maintenance checklist. Ensure tank is in good operating condition. 2 12 Maint. RANKING OF POSSIBLE FAILURE MODES Functional Failure Failure Mode RPN RCM Maintenance Task Stores no oil Tank broken or punctured 12 Perform CBM task, scheduled monitoring of tank condition Stores less than required quantity of oil Tank broken or punctured 12 Perform CBM task, scheduled monitoring of tank condition http://www.hebblehydraulics.com/fc.htm http://www.hydraulic-equipment-manufacturers.com/hydraulic-accumulator.html http://www.liebherr-conexpo.com/en-GB/128313.wfw/measure-nonMetric/tab-ContentTab128326 http://en.wikipedia. ...read more.

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