Air compressors come in all shapes and forms to meet the needs of everyday users and various industries.
Air compressors that come with a reservoir are refillable. The compressor pump pressurizes atmospheric air and stores it inside the tank to be used afterward. The process of refilling the air compressor is automatic and controlled by the pressure switch, which turns on the motor when the air pressure inside the tank drops below a predetermined value.
In this brief post, we will detail the factors that determine whether air compressors are refillable.
Are air compressors refillable?
Whether all air compressors are refillable or not depends on a simple factor; Does the air compressor have a built-in air reservoir?
If the answer is yes, the air compressor is self-refilling.
In some instances, the check valve may be faulty, leaking the air from the reservoir to the compressor head. Moreover, a leaking drain valve will empty the tank as well. However, these issues are easily resolved by replacing the defective valve. [1]
The second type of air compressor may not have an air tank. These are aptly called tankless or tank-free air compressors. One example is the power take-off (PTO) air compressors. These motors don’t have a tank, which makes them deliver pressurized air only when the motor is running.
Does an air compressor need to be refilled?
There is no need to refill the air compressor manually. The process is controlled by the pressure switch, motor, compressor pump, and air tank. These four components have an interconnected relationship that results in the filling of the air reservoir.
Some of you may be wondering why it’s necessary to fill the air compressor in the first place. This is due to a concept known as the duty cycle.
Because air compressors generate a lot of energy, the temperature of the motor will significantly increase. This is especially true for reciprocating air compressors that use pistons.
To prevent the heat from damaging internal components, the compressor motor will run in cycles. Therefore, if you intend to use pneumatic tools continuously, it will be dependent on the duty cycle of the compressor. [2]
This is where the air tank becomes handy. When the compressor motor stops, your tools will use the pressurized air stored inside the reservoir. This will allow you to run the tools nonstop.
This table showcases the on/off periods based on various duty cycles:
| Duty Cycle | Maximal On-Time | Minimum Off-Time |
| 9% Duty Cycle | 3 minutes | 30 minutes |
| 10% Duty Cycle | 3 minutes | 30 minutes |
| 15% Duty Cycle | 6 minutes | 30 minutes |
| 20% Duty Cycle | 8 minutes | 30 minutes |
| 25% Duty Cycle | 10 minutes | 30 minutes |
| 30% Duty Cycle | 13 minutes | 30 minutes |
| 33% Duty Cycle | 15 minutes | 30 minutes |
| 40% Duty Cycle | 20 minutes | 30 minutes |
| 50% Duty Cycle | 30 minutes | 30 minutes |
| 100% Duty Cycle | Offers a continuous run but requires pauses | |
| Continuous Duty | Continuous run | |
How long can you leave air in an air compressor?
Air compressors with valves and seals in a good state should theoretically hold elevated pressure for a very long time. In reality, the accessories of the air compressor (e.g., valves, seals, hoses) often leak.
Therefore, air will leak out of the air reservoir in a slow but consistent fashion. On average, an air tank will empty completely within 7–14 days, depending on the state of the seals.
According to the instructions of top compressor manufacturers, users should empty their air tanks on a daily or biweekly basis. However, there isn’t a consensus on this matter. [3]
For the purpose of safety, we recommend that you empty your air tank after every use, especially if you don’t intend to use any pneumatic tools on that same day. This will prevent any hazardous events, such as air compressor explosions.
Of course, this doesn’t mean you shouldn’t inspect the state of your seals and valves. If you notice that a valve is leaking air, it’s time to replace it. Otherwise, your operational cost and electricity bill will increase dramatically.
Related – How much electricity does an air compressor use?
Frequently Asked Questions (FAQs)
1. How are air compressors refilled?
The air compressor reservoir has a pressure switch and a built-in pressure gauge. When the pressure inside the tank drops below a certain value (i.e., the cut-in pressure), the pressure switch sends an electrical signal to the compressor motor. The latter will turn on the pump and air will get pressurized to be stored in the air tank.
In compressors with normal pressure switches, this process is automatic and doesn’t require human intervention.
2. Do all air compressors need draining?
All air compressors with tanks require regular draining to avoid the buildup of moisture and condensate.
Other benefits of draining your air compressor include:
- Prevent air compressor explosion
- Improve compressor efficiency
- Protect pneumatic tools from water and rust particles
- Enhance the quality of the pressurized air
- Prolong the lifespan of the motor and tank
If you have a tankless air compressor, there is no need to drain the compressor.
3. Why do air compressors need a tank?
Air compressors need a tank to allow for the continuous use of pneumatic tools. Without the air tank, users will have an interrupted supply of air since the compressor motor will stop periodically to cool off. When pressurized air is already stored in the tank, it serves as a second-line source during the cool-off period of the air compressor.
Takeaway message
Air compressors with a built-in air reservoir are self-refilling due to the connection between the compressor pump and the tank. Some types of air compressors are tankless and require continuous operation to deliver compressed air.
Hopefully, this article managed to answer whether air compressors are refillable or not. If you still have any questions about this topic, our comment section is always open for conversation.
