1. Introduction
In modern hydraulic systems, energy storage and pulsation dampening are crucial for system availability. Hydraulic accumulators serve as short-term energy sources to cover peak loads or to dampen pressure surges that occur during rapid switching operations. Choosing the right storage technology has a significant influence on the MTBF (Mean Time Between Failures). The use of unsuitable storage components leads to premature seal failures, leaks and inefficient system operation.
2. Physical fundamentals
The function of hydraulic accumulators is based on the compressibility of gases (Boyle-Mariotte law). For isothermal changes in state, P₀ * V₀ = P₁ * V₁ = P₂ * V₂, while for adiabatic changes in state (rapid processes) the exponential form P₀ * V₀ⁿ = P₁ * V₁ⁿ = P₂ * V₂ⁿ (n ≈ 1.4 for nitrogen) must be used. Nitrogen is the standard gas for biasing due to its chemical inertness.
3. Technical specifications & standards
The design of hydraulic accumulators is subject to strict regulatory requirements, primarily the Pressure Equipment Directive 2014/68/EU (PED) and the DIN EN 14359. accumulators must be certified for the operating pressure (up to 350 bar or higher) and the specific operating temperature. The marking must include the CE mark, PED category and permissible operating pressure (HP).
4. Selection and design guide
The choice between bladder, piston or membrane accumulators is based on the dynamic requirements of the system.
| criterion | Bladder storage | Piston accumulator | Membrane storage |
|---|---|---|---|
| Dynamics | Very high | Means | High |
| Response time | Very short | Means | Short |
| Volume range | 0.5 - 400L | 1 - 3000+ L | 0.05 - 4 L |
| pressure ratio | max. 8:1 | max. 10:1 | max. 6:1 |
| Maintenance effort | Low (bladder change) | High (seal change) | Very low (no maintenance) |
5. Installation and commissioning
The correct preload (P₀) is critical for service life. The rule of thumb is: for pulsation damping P₀ ≈ 0.9 * Pₘᵢₙ. For energy storage P₀ ≈ 0.6 to 0.8 * P₁. The filling may only be done with certified nitrogen 4.8 (purity 99.998%). Oxygen is strictly prohibited due to the risk of explosion.
6. Types of failure and causes of failure
- Bubble defects: Often caused by too rapid gas release or lack of bladder elasticity at low temperatures.
- Piston bypass: Wear of the piston seals leads to the transfer of hydraulic medium into the gas side.
- Membrane fatigue: Material fatigue after high numbers of load cycles leads to cracks in the elastomer.
7. Maintenance and condition monitoring
Condition monitoring includes regular testing of the nitrogen pressure (P₀). Sensor-based systems such as ultrasonic fill level controls or pressure sensors for analyzing the pressure-time characteristic allow a predictive maintenance strategy. A deviation of more than 10% of the target pressure requires immediate refilling.
8. Comparison matrix
| Type | Advantages | Disadvantages | Primary application |
|---|---|---|---|
| Bladder storage | Cheap, high dynamics | Risk of bubbles if gas is lost | Pulsation dampening, shock absorption |
| Piston accumulator | Very high volume, high pressures | Susceptible to seal wear | High performance memory, long storage times |
| Membrane storage | Compact, maintenance-free | Limited volume | Small systems, pulsation dampening |
9. Summary
The selection of storage technology must correspond to the specific operating parameters. While bladder accumulators excel at high dynamics, piston accumulators offer advantages at extreme volumes. UNITEC-D GmbH supports you in calculating and selecting the optimal storage components for your application. Visit our online shop: https://www.unitecd.com/e-catalog/
10. References
- DIN EN 14359: Hydraulic accumulators - accumulators for fluid power systems.
- Pressure Equipment Directive 2014/68/EU (PED).
- ISO 4413: Hydraulic fluid technology - general rules and safety requirements.
