What Is An Accumulator?
Whitepapers On Whiteboard
Miguel Vita, Freudenberg Hydraulic Division
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Hi everybody. Welcome to white papers on whiteboard. My name is Miguel Vita. I work for Freudenberg in the hydraulic accumulator division. I was invited today by our partners ESP International to talk about hydraulic accumulators.
We decided to start with the basics:
What is an accumulator?
How can I use an accumulator?
What are the different technologies that we have on an accumulator?
What Is An Accumulator? The Basic Principle.
Let’s start with – “What is an Accumulator?” Think of an air balloon inserted into a bucket and apply a force to the balloon. You increase the pressure on the airside of the balloon. This is the basic principle of an accumulator.
You have an accumulator with a hard shell. Normally carbon steel – very similar to the bucket that I showed you before, and you have an elastomeric diaphragm. This elastomeric diaphragm will make a barrier to a pre-charged nitrogen section. You can compare the pre-charged nitrogen with the air that you have in your balloon.
The port is connected to the hydraulic system. To the hydraulic system, we will apply pressure in this portion and will be translated on the same action that you have with this Force. So basically, when you have the hydraulic system, you increase the pressure in the nitrogen area.
What Happens On The Hydraulic System?
We have here a schematic of a hydraulic system.
- hydraulic cylinder
- valve pumps
- a tank
And we have added an accumulator in the system.
When the hydraulic system has no pressure, you have the pre-charge of the nitrogen using the whole cavity of the accumulator.
You have a shovel on your tractor and the shovel hits a stone. You have a huge force being applied here that will increase the pressure in the whole system. This pressurized oil will move to the accumulator and will increase the nitrogen pressure. So, this nitrogen inside the accumulator will work as a cushion. You have dampened the system using an accumulator.
Basic Functions Of An Accumulator
- Starting with the pulsation dampening. On the hydraulic system, you have pulsation. This pulsation is coming basically from the hydraulic pumps. So the accumulator will make a dampening on this pulsation and will stabilize your system. You’ll reduce the noise, you’ll reduce the vibration of the system and you’ll have the system working this move.
- Also, the accumulator can keep constant pressure in your system. If you have a leakage, for example, you’re going to lose the pressure of the system. The accumulator will stabilize the pressure and you keep the pressure at a certain level until you can stop your system for maintenance.
- Another function of the accumulator is really to be an emergency source of power in your system. For example, when you have your system being applied on hydraulic brakes and you need a sudden release of pressure in your system, the accumulator will help you release this pressure whenever it is needed.
Three Types of Accumulators
And here we come to the three different types of accumulators. We have the bladder, diaphragm, and the piston type of accumulators.
1. BLADDER ACCUMULATOR
The Bladder is the bread-and-butter. You can use bladder accumulators everywhere. Most of the hydraulic systems use bladder accumulators.
- You have a bladder bag.
- You have the pre-charge of nitrogen.
- Connected to the hydraulic system.
Those accumulators are used in pulsation dampening where you have high frequency, especially in a small amplitude. A lot of applications, right? But this type of accumulator has a restriction. The bladder has a vulcanized seam, and this is the weak point of the bladder system. If you have high frequency and high cycle demand, you can have a rupture in this seam. This is the restriction of this type of accumulator.
2. DIAPHRAGM ACCUMULATOR
Then we can go to the diaphragm type accumulator.
- Basically, the same where you have a carbon steel shell but instead of a bladder, you have a diaphragm.
- Also, the pre-charge of nitrogen and this portion is connected to the system.
Very similar applications as the bladder type accumulator. However, the diaphragm accumulator has an advantage.
Since you don’t have a seam in the diaphragm, you don’t have the restrictions that you have with the bladder type accumulator.
So applications pretty much the same, but this one is really a reliable accumulator, especially when you have high cycle demands. Applications with 1 million, 2 million, 3 million cycle demands – this is where to use a diaphragm accumulator.
3. PISTON ACCUMULATOR
- Instead of a bladder or a diaphragm, we are using an aluminum piston to make a barrier with the nitrogen.
- You keep the nitrogen pre-charged.
- The system is connected to your hydraulic system.
But really you don’t have limits for this type of accumulator.
Since you machine the accumulator, you can make it in any size. You can make accumulators with a quarter gallon. You can make accumulators with 300 gallons. You can make accumulators going to 40,000 PSI.
Custom ports, custom design, and materials so the piston accumulator is really for limited applications where you can make custom design accumulators.