Here: includes the unloader....

Air Compressor Pressure Control Switch Valve Manifold Regulator w/ Gauges Relief | eBay

wdfifteen, I can't find their website.

1990C4S, Is this the same as the one I posted above? Do you know which part is the unloader? Are the 2 brass fitting (with the little holes) are the check valve (the part that is broken on my air compressor)?

Thanks guys.

I think that the unloader is built into the pressure switch on the bottom.
It appears that the compressor discharge enters into the bottom of the pressure switch and that the pressure to the tank goes unregulated into the tank. Pressure to the lines passes through the regulator to the hose couplings.
Something that doesn't make sense to me is that the relief valve appears to be on the regulated air side of the manifold.

I got down and took everything apart to hold it on my hands and took some pics. The metal ball that popped out from the bottom of the port which connect the air hose to has nothing as a valve. At the elbow, there is hole which the ball fit tight in there. I think it's for safety as an emergency release valve, in case of over pressured, the ball pops and releases air. Why it popped while the pressured wasn't over? I think because it is too old. I pressed it back in the hole and installed everything back for right now. Let see how it goes. If I can find a better manifolds set, I would replace it.

The valve at the top where I labeled "Check valve?" has a ball and a spring inside to stop air to backward. It should be a check valve?

Question, what does the unloader do?

http://forums.pelicanparts.com/uploa...1491466334.jpg

http://forums.pelicanparts.com/uploa...1491466348.jpg

The unloader releases the pressure in the cylinder and discharge line after shutdown. This allows for an "unloaded" start. Compressor starts easier without pressure on the discharge side to overcome while starting.

The ball is there to plug a machining hole. Notice that all the other air passages can be accessed through a port, the the U-shaped passage on that side couldn't be bored without boring through the wall of the casting.

Hate to say it, but how old is the tank/compressor? and chance of rust in/on tank? maybe it's time for a new one.....

^^

My thoughts too. It might not be worth fixing. But you COULD build your own manifold for about $70.



http://forums.pelicanparts.com/uploa...1491485124.jpg

The info above (and on the previous page) is correct with respect to the unloader function.

A ball and a spring is a check valve, yes.

That ball is NOT a pressure relief, the pressure relief is the fitting with the ring on it. I can see it in your original post.

I suspect that the ball is a way to fill in a hole that is drilled as part of the manufacturing process.

Put the ball back in, add some hydraulic Loctite and center punch gently around the ball to retain it. The stand back and fire it up.

With respect to 'age'. Tap the bottom of the tank with a hammer (a pointed chipping hammer is best) to make sure the tank is not rusting out from the inside. That's how old tanks die.

I would not give up on that compressor, it is far better than most of the 'oiless' junk sold today.

As simple as that? I like it.
Question, does the check valve (valve with a ball for air go one direction?) go right before the tank, after all other components?
Do I need an unloader?

Thanks.

I did that last night and pumped it up a bit. This morning, I pumped it up to 120 PSI. It holds fine. I might adjust down a bit, maybe 110 or 115 PSI max for safety.

On tank rust, when I release air from the valve at the bottom of tank, I usually see some rusty (yellowish) water comes out first. If I do it several routes, then it's clear. So, maybe some rust.

Thanks

The check valve goes into the tank and lets air in from the compressor but doesn't let it back out. So, come to think of it, this wouldn't work as configured. The outlet to the hose needs to be between the tank and the check valve, or needs to use a separate port directly into the tank. Does your tank have more than one port into it? This switch has the unloader in it. It lets the air out of the pipes between the check valve and the pump so when the pump starts it starts from zero pressure so it can get going.

I see. Thanks. The only thing I see is on the pump, there is a hole and air coming out a bit when it's running

That switch has an unloader, the fitting on the bottom of the switch. You just need another T on the pipe fittings with a small tube (1/8", whatever size the fitting on the switch is) running from before the check valve to the switch.

If your motor is starting up fine without an unloader, then it likely has the small hole in the piston top that acts like an unloader.

my tank has 1 port only. I can have the check valve above tank and the air hose.
Thanks

If the compressor starts again when the air pressure drops then you know you do not have an unloader problem.

it does. Thanks.
Now, I wonder what that metal ball (which pressed into the hole) is for. Is it really for overloaded pressure as safety feature? If I do not need that, I can just glue/weld it in and be done.