Machinery Lubrication

Machinery Lubrication November December 2015

Machinery Lubrication magazine published by Noria Corporation

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26 | November - December 2015 | What do you normally cover in your plant's safety meetings? Personal protective equipment, chain guards, safety harnesses and lock- out-tagout procedures are common topics. When was the last time hydraulic accumu- lators were discussed? If your plant is like most, the answer is never. Why? In most plants, maintenance, production and safety managers are not aware of the dangers. Nevertheless, accumulators can present a safety hazard if the potential risks are not understood. Accumulator Function and Pre-Charging An accumulator is a storage device in a hydraulic circuit. It is the hydraulic equivalent of a capacitor in an electrical circuit. The two most common kinds of accumulators are the bladder and piston types. The bladder (Figure 1) is nothing more than a rubber balloon that separates the hydraulic oil from the dry nitrogen. Dry nitrogen is used to fill the inside of the bladder to a pre-charge level. The nitrogen pre-charge is usually half to two-thirds the maximum pressure in the system. When the pump is turned on, the nitrogen is compressed to the maximum pressure in the system. The setting on the pump compensator spring will determine the maximum pressure when a pres- sure-compensating pump is used. The relief-valve setting controls the pressure in a fixed-displacement pump circuit. In Figure 2, the bladder accumulator has been pressurized to 2,000 pounds per square inch (psi). The piston in a piston-type accumulator (Figure 3) separates the nitrogen from the hydraulic oil. When oil is ported into the By Al Smile y, GPm HydrAulic conSultinG HYDRAULICS Dangers of Hydraulic The Safety Accumulators 1000 PSI PSI PSI 0 2000 A B 2000 PSI Figure 1. Bladder accumulator Figure 2. Bladder accumulator pressurized to 2,000 psi Figure 3. Piston-type accumulator

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