Pulsation Dampening in a Hydraulic System with an Accumulator
Hydraulic systems are used in many industrial applications to power machinery and equipment. Pressure spikes, pulsations, and shocks caused by valve closures and pump operations can cause challenges in their operation, impacting the system’s performance and reducing the components’ efficiencies through wear and tear. Using an accumulator in a hydraulic system is one way to avoid pressure fluctuations and ensure smoother and more reliable operation.
Using an accumulator for hydraulic piston pumps
Design engineers often prefer hydraulic piston pumps, which are small in size and can handle high pressures. These positive-displacement pumps generate pulsations with the stroke of the piston. Like shock waves, these pressure waves create vibrations that can harm system components. The use of a properly-sized accumulator can protect against these vibrations.
What are hydraulic accumulators?
Hydraulic accumulators are energy storage devices that store (potential) energy through the compression of a dry gas, usually nitrogen, in combination with hydraulic fluid, typically hydraulic oil. Among the commonly used accumulators are bladder and piston types, with compressed gas accumulators being the most widely used due to their versatility and effectiveness.
Understanding pulsation dampening:
Pulsation dampening is required in hydraulic system design to minimize pressure fluctuations. When hydraulic valves close abruptly or pumps operate intermittently, pressure spikes and vibrations occur, potentially damaging components over time and reducing system efficiency. Using an accumulator in a hydraulic system to dampen pulsation is one way to cushion pressure spikes, pump pulsations and load reactions to ensure steady and smooth operation, especially for sensitive applications.
How hydraulic accumulators work for pulsation dampening:
The working principle of hydraulic accumulators for pulsation dampening is simple yet effective. During regular operation, the accumulator remains charged with compressed nitrogen, ready to respond to sudden pressure fluctuations. When a pressure surge occurs, the hydraulic fluid is forced into the accumulator, compressing the nitrogen, and storing potential energy. As the pressure in the system stabilizes, the accumulator gradually releases the stored hydraulic fluid back into the system, dampening pulsations and ensuring smooth fluid flow.
When is an accumulator in a hydraulic system used in pulsation dampening?
When incorporated strategically, accumulators act as dampeners during pressure surges by absorbing this excess hydraulic fluid and releasing it when needed.
Applications for using an accumulator in a hydraulic system to dampen pulsation
Pulsation dampening using hydraulic accumulators finds a broad range of applications across various industries, including:
- Industrial Machinery: Dampening pressure fluctuations in heavy machinery, such as presses and crushers, for consistent and controlled operations.
- Oil and Gas: Ensuring smooth and reliable fluid flow in drilling and wellhead control systems and minimizing wear and tear.
- Automotive: Smoothening fluid flow in hydraulic brake systems to improve braking performance and reduce noise.
- Construction: Dampening pulsations in hydraulic systems of construction equipment for enhanced precision and stability.
- Marine: Accumulators can stabilize hydraulic systems on ships and vessels to reduce vibrations and enhance manoeuvrability.
Using an accumulator as a pulsation dampener for hydraulics can be helpful in emergencies such as electrical power failure. It can also compensate for fluid losses from leakages in components like cylinders and valves. Pulsation dampeners can absorb pressure variations caused by temperature fluctuations in a closed hydraulic system and supplement pump performance during peak demand to conserve the energy of a smaller pump and motor.
For a hydraulic pump, the pistons in the pump rotate from low to high pressure, creating a ripple. An accumulator cushions against these pulsations and can reduce the noise caused by relief valves, pulsations, and system shocks. In addition, using an accumulator as a pulsation dampener can improve response times by enhancing the effectiveness of fast-acting valves to provide an almost instant fluid supply.
Selecting the right accumulator
The type of accumulator, intended function, and system operating parameters can affect the selection and sizing of an accumulator. Accurate calculations based on fluid volume requirements, working pressures, peak demand, and operating temperatures are also important when sizing and placing an accumulator in a system.
When sizing a pump for pulsation dampening, the type of piston pump must be considered. The number of pistons establishes whether the pump is simplex (one cylinder), duplex (two cylinders), triplex (three cylinders), and so on. Each additional cylinder introduces another sine wave into the system as the pump strokes, resulting in complex vibrations.
It is also important to determine if the pump is single or double acting. A single-acting pump fills the cylinder as the piston strokes in one direction (called the suction stroke), then forces the liquid from the cylinder on the return (discharge) stroke. A double-acting pump fills one end of the cylinder as it discharges liquid from the other end. As the stroke returns, the end of the cylinder, which was just emptied, fills, and the opposite end then empties.
Taking this information into account, select the pump output coefficient. A double-acting triplex pump, for example, has an output coefficient of 0.06. Next, multiply the bore and stroke of a single piston by the number of cylinders in the pump to determine piston area and stroke.
Finally, consider operating pressure and maximum allowable shock pressure. As previously stated, when sizing for shock suppression, a good rule of thumb sets allowable pressure 5% above system pressure.
However, when sizing for pulsation dampening, a good baseline for the maximum shock pressure is 100 psi greater than the maximum system pressure. The accumulator’s location in the circuit is also important. For best results, this is typically at the pump outlet.
Final thoughts
Hydraulic accumulators are essential for the smooth and efficient operation of hydraulic systems by dampening pulsations and pressure fluctuations. By storing potential energy during pressure surges and releasing it strategically, they mitigate the adverse effects of sudden valve closures and pump operations. Understanding pulsation dampening with hydraulic accumulators empowers us to employ systems that operate seamlessly, unlocking new levels of efficiency and reliability.
For specific sizing assistance and application guidance, call us at 1-800-367-4180 (toll-free). Our team of experts is ready to help you ensure the trouble-free operation of your hydraulic systems or pumps. Contact us and we will answer questions about things you’ve previously tried gone wrong.