Accumulators in general
One of the main tasks of a hydraulic accumulator is storing a certain amount of (hydraulic) fluid under pressure and wholly or partially discharging this when necessary. Because of the way a hydraulic accumulator works, they are seen as a pressure vessel that should be able to operate at maximum working pressure and should comply with regulations that are required in different countries. Accumulators with a partition between the fluid side and the gas side which is usually pre-filled with nitrogen, are often applied in hydraulic systems. There are different types of partition available that determine the design and shape of the accumulator.
LA - LAS bladder accumulators
For many hydraulic accumulators a bladder is used as partition between the fluid side and the gas side of the accumulator. These maintenance free accumulators are designed in such a way that repairs can easily be made. A bladder accumulator is manufactured from a steel tube made of hardened steel. A rubber bladder separates the gas from the hydraulic fluid. When pre-filled a robust steel knob seals off the hole at the fluid side and this prevents the bladder from being pushed out of the accumulator. Bladder accumulators should be mounted horizontally or vertically with the charging valve pointed upward.
- Robust design
- Maintenance friendly
- Quick and easy installation
- Compression ratio max. 6:1
- Energy storage in systems with interrupted operation for power reduction of the pump
- Energy storage for emergency back-up systems when the pump does not work or during electricity failure.
- Compensation for loss through leakage
- Pressure compensation
- Damping of vibration
- Volume compensation in case of pressure and temperature fluctuations
- Hydraulic suspension for vehicles
- Shock absorbers for mechanical influences
Collars for accumulators
An accumulator should be properly attached. Most accumulators are quite heavy. Because of this Findynamica has a large range of collars in stock so every accumulator can be mounted safely and securely.
Pre-filling your accumulator at Findynamica
When you need an accumulator it is quite easy to arrange for the accumulator to be pre-filled with nitrogen. At Findynamica we have the possibility to fill your accumulator which makes it directly available for mounting within your hydraulic system. Findynamica also sells complete devices for pre-charging if you prefer to fill the accumulator yourself
The status of the accumulator
To make the right calculations different factors concerning accumulator, working pressure, pre-fill pressure, required volume and working temperatures should be taken into account.
- P0 = (nitrogen pre-fill pressuren) and V0 = (actual gas volume) indicate the pre-fill status. The hydraulic pressure is lower than the pre-fill pressure, the pre-fill pressure is so high that there is no fluid present in the accumulator.
- P1 = (minimal working pressure) and V1 = (gas volume at pressure P1) indicate the status at minimal working pressure. Always make sure there is a slight amount of oil present in the accumulator to prevent the membrane from hitting the outside shell.
- P2 = (maximum working pressure) en V2 = (gas volume at pressure P2) indicate the status at the membrane at maximum working pressure. At that point the membrane has been fully pushed in and the accumulator is filled with oil.
Calculating pre-fill pressure
The pre-fill pressure depends on the application it is used for.
- In case of energy storage, emergency function, hydraulic suspension, pressure compensation, leakage compensation and volume compensation the pre-fill pressure (P0)) is usually 0,9 to 0,95 times the minimal working pressure (P1) (at maximum working temperature). The compression ratio must be the same or lower as the maximum compression ratio indicated in the product catalogue.
- In case of pulsation damping, the pre-fill pressure is 0,7 to 0,9 times the working pressure.
The working temperature can strongly influence the pre-fill pressure of the accumulator. When the temperature is increased, the pre-fill pressure will also increase. When the temperature is lowered, the pre-fill pressure will also be lower. To optimally use an accumulator when the temperature fluctuates it is important that the pre-fill pressure is calculated in the right way.
P0 (T20) = P0 (Tx) x (20 + 273 / Tx + 273)
P0 (Tx) = gas pressure P0 at measured temperature Tx
P0 (T20) = nitrogen filling pressure P0 at 20°C