Need advice on a pressure switch, please

[FTG-05]

I just bought a used IR 7.5/5* hp 80 gallon air compressor and I temporarily hooked it up yesterday and it looks like the pressure switch is fubared.

As near as I can tell, I do not have a magnetic starter, hence I need a PS rated for a 7.5/5 hp motor. So far, the highest rated PS I've found is a Square D rated at 25 amps. I called Eaton yesterday about their SQ PS, but then the return call got lost due to bad cell service here, so I won't be able to talk to them until Monday.

Here's some pics of the pressure switch and motor, please let me know what you see and think. All current wiring will be replaced, so don't worry about that. The box on top of the motor has the motor wiring and 3 capacitors.

Thanks,

* OEM was 7.5 HP; some time in the past, it was replaced with an IR 5 HP motor. I would like to size it all to 7.5, just in case.

 

[stonesfan68]

That's not an IR compressor. Somebody replaced the 2475 with another brand. In terms of the pressure switch you'll have to slug through the Square D website until you find what you need. I'll be in the office on Monday and can look up the part number.


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[FTG-05]

So you're saying the compressor pump was replaced as well? It's hard to read any placards on the thing since it was used in an auto paint and auto body shop.

Here's the model number of the compressor (upper left corner): TS7N7.5

Thanks for the help!

 

[firebox40dash5]

I'd cruise CL for some equipment that's beat to **** but has a mag starter... or just a mag starter by itself. Seen a few too many pressure switches weld the contacts shut running full line power through them. With the switch just running the contactor, a cheap, widely available switch will last you ages.

One to watch for however, is to make sure whatever overload the starter has can be had in a high enough rating to run your setup. I reused one that came with the compressor we bought as a 3P, and needed the highest capacity heater coils available for it. They were pretty hard to source, and cost $80 for the set of 3 (even though we only needed 2 for 1P).

 

[stonesfan68]

That is definitely not an Ingersoll-Rand compressor. I'm not saying it is a bad compressor, just that it is not an IR.

My guess based on most commercial customers who buy low-end compressed air equipment is that the IR pump could not keep up and so it was replaced when it wore out because the price of the pump is nearly the price of a complete machine. Who knows why the motor was downgraded to a 5HP? In any case you have a two-stage compressor for not too much money and only need a few parts to get it running.

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[MacMcMacmac]

That's a Leroi Dresser pressure lube, maybe a 400/440/500/550 and about 1000X better quality than whatever pump IR put on it originally. You will not run this through a pressure switch for very long. You need a mag starter.

 

[FTG-05]

I'd cruise CL for some equipment that's beat to **** but has a mag starter... or just a mag starter by itself. Seen a few too many pressure switches weld the contacts shut running full line power through them. With the switch just running the contactor, a cheap, widely available switch will last you ages.

One to watch for however, is to make sure whatever overload the starter has can be had in a high enough rating to run your setup. I reused one that came with the compressor we bought as a 3P, and needed the highest capacity heater coils available for it. They were pretty hard to source, and cost $80 for the set of 3 (even though we only needed 2 for 1P).

So what I think I hear you saying is get one of these 20 amp 140-175 psi pressure switch here for $10: http://www.surpluscenter.com/Electr...GLE-PORT-20-AMP-PRESSURE-SWITCH-4-1819-H1.axd

And then a magnetic starter for a 7.5 hp motor that is rated for 50 amps for $60 here: http://www.amazon.com/dp/B009W5XQMI/?tag=atomicindus08-20

For $70 plus shipping, I would have a pretty bombproof air compressor set up - yes?

Thanks for the help, I appreciate!

 

[FTG-05]

That's a Leroi Dresser pressure lube, maybe a 400/440/500/550 and about 1000X better quality than whatever pump IR put on it originally. You will not run this through a pressure switch for very long. You need a mag starter.

I'm not sure what you're saying here: Sounds like I got craigslist-ripped-off big time???!!!

Ok, just messing with you! I'll take a look at the pump tomorrow and see if I can find any ID numbers. There is a nameplate, but it is oversprayed, just like the rest of the pump.

Thanks,

 

[MacMcMacmac]

If the hydraulic unloader setup is working properly, you should use it to unload the pump instead of a pressure switch with a needle valve. This way, it is protected if for some reason it fails to build oil pressure. You will need to run an air line from the tank, through the unloader mechanism on the very end of the compressor which has a line going from it up to the big cap on the heads. Inside these caps, there is a plunger, a spring and some fingers to hold open the intake valve. When the compressor shuts off, oil pressure drops, and the unloader at the back of the pump opens up and lets air go to the plungers inside those caps to move them downward and push open the intake valves. This releases pressure from the cylinders and lets the compressor start with no load (very important). When it restarts, the intake valves are left open until the oil pressure builds and cuts off the air signal to the plungers, which then retract under spring pressure which lets the valves operate normally. It is a superior system of unloading a compressor and protects it from a low oil pressure condition. If you get a pressure switch, get one with a blowdown valve, just in case this system is inoperative, but I would try to get it working first. If it doesn't work for some reason, you can just hook up the blowdown line to the pressure switch needle valve and unload it that way.

 

[FTG-05]

Mac, I *thnik* I know what you're saying but I'm not sure how I would implement it. The tank has an unloader valve plumbed right below the pump inlet tube (that's now removed, see pics).

More pics of the pump:

If you look closely, you can see that someone used teflon tape on the compression fitting into the tank (left side of inlet tube).

I *think* the copper tubes you see going to the lower center of the pump are the tubes that Mac's talking about. You can see one tube apparently cut off directly in front, horizontally and there is another cut off tube just below it, going straight down.

Pump nameplate, obviously over sprayed. Anyone know of a good way to get the paint off without damaging the nameplate info?

 

[Charles (in GA)]

You need a mag starter. I'll bet the motor does not have any internal thermal protection, that is one of the things a properly set up mag starter does, along with saving your pressure switch.

You can opt for changing the pressure switch every year or two for forever, or you can install a mag starter and not worry about it ever again.

Charles

 

[FTG-05]

You need a mag starter. I'll bet the motor does not have any internal thermal protection, that is one of the things a properly set up mag starter does, along with saving your pressure switch.

You can opt for changing the pressure switch every year or two for forever, or you can install a mag starter and not worry about it ever again.

Charles

You mean like post #7?

 

[MacMcMacmac]

Looks like a 400 by the look of that tag. Try some rubbing alcohol, that paint looks a bit soft to me.

In the second pic, the hydraulic unloader is the device right in the middle, with the square cover with the four screws in it. You feed it air from the tank, and oil pressure does the rest. There is an Allen head plug around 2 O'clock on the round cover just behind it for an oil pressure gauge. I can't recall if the air goes in the back or the bottom right now, it's been about 20 years since I worked on one, but there are Leroi pump pictures around this site to show you the correct installation.

 

[FTG-05]

Looks like a 400 by the look of that tag. Try some rubbing alcohol, that paint looks a bit soft to me.

In the second pic, the hydraulic unloader is the device right in the middle, with the square cover with the four screws in it. You feed it air from the tank, and oil pressure does the rest. There is an Allen head plug around 2 O'clock on the round cover just behind it for an oil pressure gauge. I can't recall if the air goes in the back or the bottom right now, it's been about 20 years since I worked on one, but there are Leroi pump pictures around this site to show you the correct installation.

Good catch on the "400"!!! I just looked at the original high resolution pic and noticed the 400 almost immediately! Thanks! I'll try the alcohol bit and see if I can safely clean the tag.

The oil pressure/unloader business you're talking about is *slowly* getting clearer, but I feel I'm far from understanding it yet. You said hook it up to the outlet in the center: which one? The horizontal or the vertical one?

The bad news is this oil pressure/unloader thing will have to take a back seat to getting the thing wired up, which is the next order of business. And as Charles (in GA) noted, I need a good mag starter first.

I linked to one earlier, but have no clue if it's a good unit or if I should get another or better units etc. Recall that I want a mag starter that will handle a 7.5 hp motor even though the original 7.5 was replaced with a 5 hp. The good news is that the new pressure switch I plan to get (also linked to earlier) will have four outlets, so I'm hoping one of those could be used for the oil pressure/unloader on the pump.