- Materials & Industrial Technology
Selecting and Replacing an Air Compressor Pressure Switch
Almost every air compressor have a pressure switch. The pressure switch tells the air compressor when to start and to stop.
The pressure at which a pressure switch closes is the cut-in pressure.
The pressure at which a pressure switch opens in the cut-out pressure.
The cut-in pressure should always be the lowest allowable pressure in your air system. If, for example, your equipment needs 100 psi to operate, set the cut-out pressure above 100 psi.
Since you will always have some pressure drop in your compressed air system, and since it takes some time for the compressor to 'kick in', it's better to set the cut-in pressure 10 psi higher. In our example, we would set the pressure switch at 110 psi to allow for the pressure drop in our system.
The difference between the cut-in and the cut-out pressure is the pressure differential.
Pressure switches for air compressors come in different forms and shapes.
Some pressure switches have a fixed cut-in and cut-out pressure set-point. Other pressure switches have a fixed pressure differential, while the cut-in pressure can be adjusted.
On other types of pressure switches you can adjust both the cut-in and the cut-out pressure.
It's up to you what you need. Fixed pressure switches are usually a little cheaper, while fully adjustable pressure switches give you more freedom.
Finding a good replacement pressure switch
An exact replace from the original manufacturer is often very expensive. It is usually much cheaper to go out and find your own replacement switch.
There are plenty to be found on eBay, Amazon and specialized (online and offline) stores.
Your new pressure switch need not be completely the same. However, you need to buy one of the same maximum pressure and electrical rating.
Here is a list of things to check before you buy:
- Is the maximum pressure rating equal or higher than the current one?
- Can it handle the electrical load?
- What are the physical connections for compressed air?
- Does it have an on/off switch or not?
- Does the old pressure switch have an i(integrated) unloader valve?
Now, let's look at each of the above points.
Your compressor is rated for a certain maximum pressure. Your new pressure switch much be rated the same, or higher pressure.
Also, be sure to never set the pressure setting higher than the maximum rated pressure of your compressor!
On smaller compressors (0 - 3 hp) the pressure switch will switch the compressor motor directly.
Your new pressure switch needs to be able to handle the motor currents of your compressor.
What are the physical compressed air compressor on your current pressure switch? You can always make an adapter, but it's easyest to buy a new pressure switch that fits directly on your compressor.
Common connection sizes are 1/4", 3/8" and 1/2" NPT female.
Some compressors have an on/off switch, some don't.
Bigger compressors usually don't have an on/off switch on the pressure switch. Instead, they have a separate control panel where the control buttons (on/off, load/unload) are located.
Smaller compressors are switches on and off directly by the pressure switch. In this case, your pressure switch will most likely have an on/off button
The unloader valve of reciprocating compressors is often located on the side or on the bottom of the pressure switch.
The new pressure switch that you buy must have the same connections (so you can re-use the old unloader valve), or must come with a new unload valve.
If you buy a new pressure switch together with an unloader valve, make sure that the physical compressed air connection is the same.
Go get one!
With all the things to think about when buying a replacement pressure switch, it may seem like a very difficult task.
But, in general you should be able to find a matching pressure switch fairly easily. Pressure switches are standard components and you surely will find one that fits your needs.