Air compressor press. switch question

My pressure switch failed the other night, the compressor did not shut off, thankfully the safety valve worked as advertized.
So, I need a new pressure switch for my old compressor, which has no unloader, no check valve, etc. I'd like to correct that.

Right now, the switch is set on it's own line coming off the tank, all by it's lonesome.

I'm looking at the Furnas switches like this - Furnas 1 Port Pressure Switches which has an integral unloader.

So I get that I need a check valve on the line to the tank. And it looks like the Furnas switch is to be on the line - at some point - such that the unloader can dump the air between the pump and the check valve.
If it's upstream of the check valve, and the unloader dumps the air, then isn't the switch seeing -0- psi, which would then kick the motor off again?

I see check valves with 1/8" npt taps which mention being lines to unloaders or "control lines" Shorty Check Valve

does the pressure switch (w/ unloader) run off a line from this port on the check valve?

thanks in advance for any wisdom.

Hi Rudd,

I usually use a 1/4" compression to 1/8" NPT fitting in the check valve. I then run a piece of 1/4" copper tubing from the check valve to the unloader valve on the pressure switch. Most pressure switch unloader valves I have seen are already set up with a 1/4" compression fitting.

The pressure switch still sees whatever pressure is in the tank at its inlet port. The unloader valve is separate from this air circuit. When the switch contacts are open the unloader valve opens exhausting air from the line between your compressor head and the inlet check valve you have installed in the tank. This reduces the pressure on the head to 0 PSI making for an easier start. When the tank pressure drops to the switch's cut-in pressure, the unloader valve closes so no air is lost during pump up. The check valve ensures that air in the receiver will not vent when the unloader is open. Hope this helps

that Sir, is an immense help. I didn't understand that there are -2- connections to the pressure switch, one for pressure sensing, one for unloading.

I bought from this guy before with no issue. eBay compressor-source
No relation.
-Tim

If you have to order it anyway look on Ebay you can save a bunch of money. they have many diferent brands of switches and you can also find a check valve with unloader port that will fit your tank. Youl need to take your check valve out first and see what size and threads are on it. And you never now you might have a port already on yours just blocked off.

one other thing to look at is what size motor is on your compressor and the amp rating of it. Not all presure switch can handle high amps.

I bought a cheap 10$. switch of ebay for my big compressor and its working fine. But i also only runing low amps through it since I have a magnetic starter. and its only six mounths old so ill have to see how it holds up

In my experience, a Square D switch will last a lot longer than a Furnas switch.
Mike

I looked at Square D -
They seem to have adjustable set points, which is a plus. The ones I saw did not have integral unloaders.
I'd already dropped the hammer at some web store called "Master Tool Repair" before I heard the Ebay advice, two business days ago. Noted my card had not been charged as of this morning, called them up, "one part is on backorder and one is on partial backorder" - when it plainly states they will notify you of backorders.
I got the feeling they are drop shipping stuff and don't actually stock the items they offer. So I cancelled with them this morning and went another direction.
It's amazing though, the pressure switch seems to be an item MSC does not carry!