A hydraulic (also called ‘hydroaccumulator’) is a device being used for storage working fluids under high pressure, which is generated by various
external factors, and for exchanging energy of compressed fluids into mechanical energy.
Hydroaccumulators ensure more constant and efficient work of hydraulic systems.
Over the years, there were invented and used several types of hydraulic accumulators
which differ in structure and factors used for pressurising fluids.
This article briefly discusses types of hydroaccumulators most commonly used
nowadays, their structure, principles of operation and usage.
Types of hydraulic accumulators
There are several types of hydraulic accumulators because of their structure and factors serving to pressurising fluids.
Three main types of hydroaccumulators are:
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raised weight accumulators
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spring accumulators
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gas-charged accumulators.
Gas accumulators are most commonly used in machines. They are divided as follows:
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direct contact accumulators
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piston accumulators
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diaphragm accumulators
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bladder accumulators.
Structure and principles of operation of hydroaccumulators
To put it simply, a hydraulic accumulator is a kind of a container (reservoir). Its outer shell (cylinder) is built of metal (carbon or stainless steel or aluminium) and absolutely hermetic. It contains fluid (usually oil or water) which is stored under a very high pressure.
A raised weight accumulator is equipped with a piston. A pump pumps a fluid to a cylinder raising a piston with a sealing ring. The weight of piston keeps a constant pressure of fluid.
A spring accumulator works in the same way as a raised weight accumulator does. Pressure of fluid is kept by a spring that presses on a piston which in turn presses on fluid. The spring is pressed by a cylinder head cover.
A gas-charged accumulator is filled with a compressed gas - usually air or nitrogen. A pump pumps a fluid into a cylinder. Compressed gas is pressed through a valve to a cylinder and it regulates pressure of fluid.
In direct contact accumulators, gas has a direct contact with fluid. In case of piston, diaphragm and bladder accumulators, gas is separated from fluid with a piston, a diaphragm or a bladder, respectively.
Usage of hydraulic accumulators
Hydraulic accumulators are commonly used a.o. in hydraulic power packs of industrial machines and devices, in elements of hydropneumatic suspensions of various vehicles (road vehicles, tractors, aircrafts), construction machines (e.g. concrete mixers) and self-driving machines (e.g. robots).
These devices also reduce pressure waving in hydraulic circuits and prevent cavitation, keep both appropriate volume of fluid and volume of pressure in case of system failure or when hydraulic pumps are out of order. Moreover, they reduce shocks and pulsations, compensate leakages and fluctuations of temperature in a system.
A hydroaccumulator stores energy and gives it back in moments of increased demand for energy so it is rather an energy reserve than a permanent source of energy.
Summary
Hydraulic accumulators are undoubtedly very useful devices. They make it possible for hydraulic systems to cope with a higher demand for energy with using less powerful pumps, to respond more quickly to a temporary higher energy demand and to reduce pulsations as well as to ensure permanent and efficient work of pumps. For these reasons, hydroaccumulators guarantee better efficiency of hydraulic systems, help to protect them from damage as well as limit using big hydraulic pumps powered by big electric engines. All these factors significantly reduce costs of operation and maintenance of hydraulic systems.