Just a few days ago I received a comment on Silent airbrush compressor article with a question about air pressure switch. The question was really reasonable because I actually never included any exact instruction on how to set up a pressure switch. I was thinking to update the article, but after a while I decided it will be better just to write another entry. The previous article was too long already and I didn’t want to make it even longer, otherwise nobody will read it untill the end.
The question came from Narain and I want to thank him for bringing this up.
Good morning ! Please explain me how to adjust auto switch screw for cut off / on. In the picture there are two screws, one is with small spring and other with big spring. Which screw is for cut off and which is for on. What is the position of both screw before adjusting them, fully loose or tight. Thanks.
So I’m going to answer the question and I will add some info about wiring the pressure switch as well, so the information about air pressure switch will be more complete.
How to Adjust Air Pressure Switch?
Before you even start setting up the switch you should have your tank filled up with the air because first you have to set the minimal pressure for your tank. So, when you will lose some air you will see when the switch goes on. To see the pressure values you should have the gauge (manometer) connected to your tank. Here I have to include the picture that you better see how it works.
The small spring “number 1 on the picture” is called differential spring and it sets the difference between “on” and “off” cut points. When you start setting your switch you should fully tight the differential spring (1). Then start tighten up in small steps the big spring (2). Then release air from tank and watch the pressure on your gauge (manometer). With this spring you will set the “on” pressure (minimal pressure) you need.
Only when you’re done with setting the minimum pressure go back and loose up the differential spring (1). By expanding the pressure difference and under condition that minimal pressure limit stays unchanged (exactly where you set it up – big spring) you actually set up the cut “off” pressure (maximal pressure) you need. To check this value you will have to pump some air into tank and watch the gauge again.
I think that this explanation is good to go even for beginner.
Now as I promised I will explain how to wire the pressure switch.
Air Pressure Switch Wiring
Before you do anything about wiring, unplug your power cord from the socket!!!
Switch off the power that feeds the compressor circuit while you are wiring the pressure switch. You can either switch “off” the circuit breaker or pull the fuse that controls the power.
As you can see on this picture the pressure switch has a lot of contacts on the unit called “control terminal of the pressure switch“. In this particular case it has three lines of screws. The top line of terminal has three screws (1, 2, 3) to connect the compressor (depends on compressor, if it has only one phase than you can connect up to 2 compressors to one pressure switch). The second line of terminal ( 01, 02, 03) is for power cord. The bottom line has two screws to connect the grounding.
Each set of contacts (01-1 with 02-2 or 03-3 with 02-2) can act like a single switch where 02-2 is for neutral wire. If you have one compressor that you want to regulate with this air pressure switch than use screws 01 and 1 to connect the phase L1 and 02,2 to connect neutral wire N, and one of grounding screws to connect the ground wire G. So you don’t have to use all of them. You will need three-wire cable with brown (L), blue (N), yellow-green (G) for 230V or white (L), black (N), green (G) for 115V. Always start with connecting the ground (G). While connecting you will need to remove about half-inch of the plastic insulation to expose the copper wire. Tighten the exposed part of wire under heads of screws very good that it won’t become loose.
Don’t forget to put the cover back on the pressure switch before testing
This is it. I hope this small “how to” will help you with your home project. If you have any other advises that can cover this topic in more detail, please don’t hesitate and leave your comment.