Hydraulic accumulators are common parts of hydraulic systems. But many people don’t know how they work. This article will explain how a hydraulic accumulator works. It will describe the changes in the internal oil and gas during the pressure increase, stabilization, and decrease phases. It will show you how the hydraulic system works.
What Components Are Inside a Hydraulic Accumulator and Which Parts Move During Operation?
A hydraulic accumulator has three parts: the gas side, the fluid side, and the separating element. The separating element can be a bladder, a piston, or a diaphragm. The way they work is basically the same, no matter what they are made of.
Only the separating element inside the accumulator moves when the system is operational. When the pressure in the system changes, hydraulic fluid enters or leaves the accumulator. This pushes the separating element and expands or compresses the internal gas. The gas is used to store and release energy, while the hydraulic fluid is responsible for transmitting pressure and flow. The hydraulic accumulator is part of how the system works.
What Does “Precharge Pressure” Mean in The Hydraulic Accumulator Working Principle?
The pressure of the gas side before the system starts is called the pre-charge pressure. This initial pressure determines the position of the separating element when the system is not pressurised, and decides when the accumulator starts working with the system.
When the pressure in the system gets higher than the pressure before it is filled, the fluid is pushed into the accumulator. The separating element begins to move and compress the gas. When the pressure in the system goes down and is lower than the pre-charge pressure, the gas inside the accumulator pushes the fluid back into the system.
How Does a Hydraulic Accumulator Behave When the System Is Idle?
When the hydraulic system is not working, such as when the equipment is not operating or the relevant valves are closed, the pressure in the system may be zero or kept at a relatively stable level. In this case, the separating element inside the hydraulic accumulator is in a fixed position, and there is a balance between the gas and the hydraulic fluid.
At this point, the hydraulic fluid will not continuously flow into or out of the accumulator. The accumulator will not take part in the system’s operation. The position of the separating element will only change when the system pressure changes. You can think of this stage as the start of the entire working process. All later oil filling or draining processes are based on this first state.
Typical Applications of Hydraulic Accumulators in Industrial Systems
Hydraulic Press System
Hydraulic presses need a fast and powerful hydraulic system to do stamping jobs.
When you switch on and off the press, the accumulator helps to keep the pressure in the system steady.
When the hydraulic pump is working, the accumulator stores excess hydraulic oil, so that the pump doesn’t have to be switched on and off so often.
If the demand for oil changes during stamping, the accumulator releases the stored oil. This allows the system to provide a large flow rate quickly. This prevents the system from shutting down because of low pressure.
Construction Equipment
Construction equipment such as excavators often needs powerful and fast hydraulic systems to do different jobs, like lifting and rotating the bucket.
Accumulators can reduce the strain on the hydraulic pump and save energy when the pump is switched on and off a lot.
If the load changes quickly, the accumulator can absorb extra fluid and release it when the pressure drops. This makes sure the system pressure stays steady.
Accumulators help to protect the system against shocks, reduce vibrations during operation, and prevent wear and tear to the equipment caused by changes in pressure.
Mining Machinery
Mining machinery needs hydraulic systems to power the lifting and tilting movements of mining carts.
When the mining cart is being lifted and lowered, hydraulic accumulators provide a short burst of pressure to the hydraulic system to help it stay stable during changes in load.
The accumulator stores and releases fluid, which prevents the hydraulic pump from frequently starting and stopping during load changes, reducing the pump’s workload.
The accumulator helps to keep the pressure stable when it changes a lot. This stops the machine from getting damaged by big changes in pressure.
Wind Turbine Control System
In the hydraulic control system of wind turbines, hydraulic accumulators control the wind turbine’s yaw and pitch angles. This makes sure the turbine can react to different wind speeds and loads.
If the pressure in the system gets too high, the accumulator stores extra fluid to keep the pressure steady.
If the wind turbine needs to respond quickly to different wind speeds, the accumulator can release the stored fluid quickly, which provides a large flow rate in a short time.
The accumulator makes the hydraulic pump less busy, which stops the pressure in the wind turbine’s hydraulic system from going up and down too much. This makes sure that the equipment works well and doesn’t break down.
Ship Steering Gear System
In a ship’s hydraulic steering system, a hydraulic accumulator is used to make sure the steering gear turns smoothly.
The accumulator helps to keep the pressure steady in the hydraulic system because it stores and releases fluid. This stops too much pressure from going up and down too quickly, so that the steering gear doesn’t get damaged.
When the steering gear needs more hydraulic fluid, the accumulator provides extra flow for a short time. This makes sure the vessel can change course quickly when it needs to.
When the pressure in the system is too high, the accumulator stores the extra fluid. This stops the hydraulic pump from being switched on and off too often. So, you’ll use less energy and the equipment will last longer.
What Happens When System Pressure Rises and Oil Enters the Hydraulic Accumulator?
When the actuator begins to move, the valve switches position, or the hydraulic pump starts operating, the system pressure gradually increases. During this process, hydraulic fluid enters the accumulator.
Step 1: System Pressure Rises
As the pressure in the system gets higher, the pressure is sent through the piping to the oil side of the accumulator. It helps the oil to enter the accumulator.
Step 2: Separator Moves and Gas Is Compressed
When the pressure in the system is higher than the pressure of the gas inside the accumulator, hydraulic fluid is forced into the accumulator. This causes the separating element to move towards the gas side and compress it.
Step 3: A New Pressure Balance Is Reached
As the gas is being squeezed, the pressure inside the accumulator keeps going up. When this pressure gets close to the system pressure, the flow rate of the fluid slows down and then stops, and the accumulator reaches a new state of balance.
What Happens to the Accumulator When System Pressure Becomes Stable?
If the pressure in the hydraulic system stays the same, the accumulator will also stay in the same condition. At this point, the separating element usually stays in one position, and fluid no longer keeps entering or leaving the accumulator. This means that the system and the accumulator are at a steady pressure.
It’s important to remember that a hydraulic accumulator is not a device that provides a constant supply of oil. It works by using the difference in pressure between the system and the accumulator. When these two pressures are the same, the pressure difference disappears, and the separating element stops moving. At this point, the accumulator will stay still, and the internal separating element will only move again when the pressure in the system changes.
What Happens When System Pressure Drops and The Accumulator Releases Oil Back to The Circuit?
When the pressure in the system drops, or when the circuit needs more flow of liquid in a short period of time, the pressure in the accumulator will fall below the pressure in the system. This will cause the accumulator to start responding to the changed setting.
Step 1: A Pressure Difference Is Created
As the pressure in the system goes down, the pressure inside the accumulator goes up. This creates a difference in the pressure between the accumulator and the hydraulic circuit.
Step 2: The Gas Gets Bigger and the Separator Moves
The pressure difference makes the gas within the accumulator expand, then pushes the separating element towards the oil side.
Step 3: Oil Flows Back and a New Balance Is Reached
The movement of the separating element causes the fluid to flow from the accumulator back into the hydraulic circuit. As the fluid is released, the internal pressure of the accumulator gradually decreases. The fluid release process stops when the pressure is balanced with the system pressure again, or when the separating element goes back to the position influenced by the pressure from the pre-charge.
How Does Separator Type Change The Working Principle: Bladder vs Piston vs Diaphragm?
There are different types of hydraulic accumulators, but they all work in the same way. When the pressure changes, the gas is either compressed or expanded. This causes the separating element to move. As a result, hydraulic fluid flows between the accumulator and its circuit.
Bladder Type: Deformation of a Flexible Separator
In a bladder-type accumulator, the separating element is a bladder that changes shape. When the pressure changes, hydraulic fluid goes into or out of the accumulator, which makes the bladder change size. This makes the gas get bigger and smaller by changing shape. This process depends on the bladder being able to change shape, not on rigid parts moving in a straight line.
Piston Type: Linear Movement of a Solid Separator
In a piston accumulator, the separating element is a piston that moves along a cylinder. When the pressure changes, the piston separates the gas from the fluid by moving back and forth within the cylinder. Because there is a contact surface between the piston and the cylinder, it takes time for the piston to move because of friction.
Diaphragm Type: Deflection of a Thin Separator
In a piston-type accumulator, the separating element is a piston that moves axially. When the pressure changes, the piston separates the gas from the fluid by moving back and forth within the cylinder. The piston and cylinder rub together, which makes it move more slowly.
How Does an Accumulator Interact With The Pump, Relief Valve, and Pressure Control During Transients?
In a hydraulic system, a hydraulic accumulator doesn’t control the pressure or directly regulate the hydraulic pump or relief valve. Its role in the system is to control the pressure by taking in or releasing oil. This affects the response of the hydraulic pump and relief valve during transient processes.
This process usually leads to the following connections being made between the different parts of the system: If the pressure in the system rises or falls too quickly, the pressure may reach the relief valve’s set value more quickly than expected. This could cause the relief valve to open too soon. If the pressure in the system falls too quickly, there may be a delay in how the hydraulic pump responds and adjusts. At this time, the release of fluid from the accumulator is part of the process that changes the pressure.
The hydraulic accumulator only has an effect on how the pressure changes, not the final pressure level of the system. The way the hydraulic pump, relief valve, and accumulator work together is set up by the pressure change process.
What Are the Most Common Misreadings of The Hydraulic Accumulator Working Principle?
People often have the wrong idea about how hydraulic accumulators work. The next section explains some common mistakes that people make when doing practical projects.
Misreading 1: Treating The Accumulator as a Second Hydraulic Pump
A hydraulic accumulator does not produce energy itself, nor can it actively supply oil to the system. It only exchanges energy with the system when the pressure of the flowing water is higher or lower than the pressure in the system. This process starts when there’s a pressure difference between the system and the accumulator, not when the accumulator is actively sending output.
Misreading 2: Assuming The Accumulator Supplies Oil Continuously
When there is a pressure change, the accumulator releases fluid. However, once the internal pressure is equal to the system pressure, the fluid flow stops. This means that the accumulator only works when there is a change in pressure and does not operate continuously.
Misreading 3: Ignoring The Threshold Role of Precharge Pressure
How the accumulator absorbs and releases fluid is determined by the pressure before charging. You can’t understand why the accumulator doesn’t take part in system changes within certain pressure ranges unless you think about this initial pressure.
Misreading 4: Explaining The Working Principle Only as “Storing and Releasing Energy”
Saying that an accumulator is just a device for saving and releasing energy doesn’t show how it actually works. The pressure equilibrium point inside the accumulator changes when the system pressure changes. This causes the movement of the fluid and the separating element around this changing balance.
FAQ
Why doesn’t the accumulator respond to changes in system pressure sometimes?
If the system pressure doesn’t go above the pressure threshold of the accumulator before it’s charged, the separating element doesn’t move much. This means that the accumulator seems like it’s not part of the system changes.
What factors mainly affect the response speed of a hydraulic accumulator?
The speed of an accumulator is mostly affected by how much the pressure changes, the resistance in the circuit, and how the separating element moves. All of these things together decide whether the fluid can get in and out quickly.
Is the pressure change inside an accumulator linear during charging and discharging?
In practice, the internal pressure of an accumulator usually does not change in a straight line. It changes gradually as the gas gets compressed or expanded.
Do circuit resistance and pipe length affect how an accumulator works?
The speed of the fluid flowing through the pipe is affected by the resistance in the circuit and the length of the pipe. This changes how the accumulator affects system pressure changes.
Do gas state changes inside the accumulator affect transient system pressure?
The changes in the gas’s state when it is compressed and then expanded affect how quickly the pressure in the accumulator changes.
Does an accumulator respond to every pressure fluctuation in the system?
The accumulator will only respond when there is a big enough pressure difference; smaller or very fast fluctuations will not be noticeable.
Final Thoughts
This article explains how a hydraulic accumulator works by looking at the pressure changes in the hydraulic system. It explains what happens inside the accumulator when the pressure gets higher or lower. If you understand how these processes work, you can see the pressure changes and how the equipment responds when the accumulator is working. This helps you to check that the system is working correctly.
Target Hydraulics has over ten years of experience with hydraulic accumulators. We can help you find the right accumulator for your needs and provide technical support. If you have any questions about accumulators in your hydraulic system design or operation, please contact us for further discussion.
