Hydraulic accumulators: know your legal obligations
1st Quarter 2009
Hydraulic systems & components
Users operating hydraulic systems for power transmission purposes may well be inadvertently operating outside of applicable government legislation. Although the applicable regulations are inconsistent, ignorance is no excuse.
Before we begin
This article contains abstracts and interpretations of South African legislation. Users of accumulators should ensure that they comply with all applicable legislation and should not rely solely on the contents and interpretations of the authors or publishers of this article.
Figure 1. Typical hydraulic safety block for an accumulator
Accumulator whys and wherefores
Hydraulic power systems incorporate accumulators to store energy, thus temporarily supplementing the hydraulic supply to the system.
Sci-Tech Encyclopedia defines an hydraulic accumulator as: “A pressure vessel which operates as a fluid source device or shock absorber. It is used to store fluid under pressure or to absorb excessive pressure increases. The hydraulic accumulator is an energy-efficient component, which allows the use of a smaller pump to achieve the same end results in terms of cylinder rod actuation speeds. In certain circuit designs, the accumulator will permit a pump motor to be completely shut down for an extended period of time while the accumulator supplies the necessary fluid to the circuit.”
Accumulators use various techniques to achieve their purpose:
* Deadweights.
* Spring-loading.
* Hydro-pneumatic systems.
Deadweight accumulators
In these accumulator designs, system pressure works against a piston which supports a weight, so the energy store is in the form of potential energy.
Spring-loaded accumulators
In spring-loaded accumulators the system hydraulic pressure pushes against a piston which is resisted by the compression of one or more springs.
Hydro-pneumatic accumulators
Hydro-pneumatic accumulators, which are also known as compressed gas (or gas-charged) accumulators, are the most common form of accumulator.
A compressed gas accumulator consists of a cylinder with two chambers that are separated by an elastic diaphragm, a totally enclosed bladder, or a floating piston. One chamber contains hydraulic fluid and is connected to the hydraulic line. The other chamber contains an inert gas under pressure (typically nitrogen) that provides the compressive force on the hydraulic fluid. Inert gas is used because oxygen and oil can form an explosive mixture when combined under high pressure. As the volume of the compressed gas changes the pressure of the gas, and the pressure on the fluid, changes inversely.²
Continued on the web
For the complete article visit www.motioncontrol.co.za/+091Q54
For more information contact Norman Hall, Hyflo Southern Africa, +27 (0)11 386 5800, [email protected], www.hyflo.co.za
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