Lost Another Air Compressor Pressure Switch

[Buffalo21]

over the last 10-12 years, I‘ve lost about 6 air compressor pressure switches. They last roughly about 2 years, then one of the contacts burns off, then I have a dead air compressor. I lost one last night, and finally decided to correct the pressure switch issue. I finally assembled enough parts to install a contactor rated for 4 times the amp draw of the motor, I picked up 2 cabinets (customer was sending them to the scrap dumpster) and work graciously donated all of the pieces and parts necessary to finish up the installation.

The air compressor runs perfectly, the pressure switch now only carries the load of the contactor coil, and hopefully will last a little longer, I have a new pressure switch on order, the one being used now has one burnt contact and one functional one, the functional one will hopefully last until the new one gets here.

 

[NC Rick]

Perhaps a diode or varistor across the contacts?

 

[Buffalo21]

Hopefully as the pressure switch will not long be switching the full motor load and now just switching the coil load, it should last a lot longer. Going from 20+ amps to about .8 amps.

 

[markba633csi]

Couldn't have done it better myself- nice color scheme too
-Mark

 

[extropic]

Have you been ordering OEM exact replacement pressure switches all along? Chinese?

 

[Buffalo21]

Same Furnas pressure switch, as came on it originally.. As for the origin of the switch source, who knows, I just get what they give me. The air compressor is powered 100% of the time, basically 24/7/365, it cycles when the switch tells it to run. Lately I’ve had worse luck with electrical parts made in Mexico, than parts made in China.

 

[mksj]

Larger compressors typically use the pressure switch to trigger the contactor, so less of an issue with failure, it was a wise modification you made. I am hesitant to leave my compressor on 24/7, I have had both the check valve from the compressor to the tank fail and have had air hoses leak/fail. Although my compressor is rated for 100% duty cycle, I have heard of others burning up the compressor/motor due to an air line rupture that was unattended. When I leave the shop I always try to remember to turn the compressor power off (turns off the pressure switch), and also close the air valve to the tank.

 

[extropic]

Same Furnas pressure switch, as came on it originally.. As for the origin of the switch source, who knows, I just get what they give me. The air compressor is powered 100% of the time, basically 24/7/365, it cycles when the switch tells it to run. Lately I’ve had worse luck with electrical parts made in Mexico, than parts made in China.

I'm disappointed that Furnas brand switches have been burning up so frequently for you.

I bought a Harbor Freight compressor to keep me going while my primary compressor was down for repair/modification.
Pretty soon, the pressure switch on the HF unit was trouble, but I got by with it and the pump, though loud, seemed to operate well enough.
The sticker on the motor cover says 2.5 HP, 120V, 14A.

Later, I decided to replace the wonky HF pressure switch to improve reliability. I bought one from McMaster-Carr because the catalog says 24A Switching Current at 120V. I received a Furnas brand switch, but it's nomenclature says nothing about "Switching Current" and is only rated for 1.5HP at 120V. WTF???

This thread has got me thinking I may need to implement a contactor to achieve reliability. Changing the PS and adding a contactor, at retail prices ($300+), looks like it will more than tripple the cost of the cheap compressor. What am I doing wrong here?

 

[Bi11Hudson]

For what it's worth department. . .
25 or 30 years ago, I was poking around a Sears store and stumbled across what was a fair deal on a compressor. Around the time Sears first started to get in trouble so it may well have been miscellaneous parts cobbled together to sell. A "DeVilbiss" compressor, an ASME tank and a name brand motor. All for the price of a Sears brand 2 HP compressor. I jumped on it. . . The compressor was rated at 13 CFM, the motor was 5 HP dual voltage. I think the only part that was Sears, besides the paint job, was the pressure switch. In any case, the switch was replaced a couple of times for burned contacts. Being in that field, electrician, led to some frustration so the last time I made a similar conversion. A NEMA size 00 starter and enclosure was installed with the pressure switch operating the starter. The overloads were not updated, it was a spur of the moment fix.

Now my comments on the subject: The pressure switch had "double break" contacts, the nature of the moving parts. There were two contacts, breaking both sides of the line, that were in place when I rewired the motor for 240 volt operation. Since adding the starter, the pressure switch hasn't been touched. 20 years????? I wired it through one set of contacts and left the other as a spare "Just In Case". There was no need to double up the contacts. Depending on the physical arrangement of the pressure switch, a single contact, single or double break, is sufficient. With the other being a "standby", requiring only two wires to be moved if ever needed. The "double break" contacts only come into their own on DC systems. AC tends to break an arc by itself.

The starter could just as well have been a heavy relay, in effect that's what the starter really is, just with an "overload" deck. Easy enough to replace, I don't know if I can even find contact kits for that particular starter these days. But I have several large relays on hand if it ever comes down to that. The bottom line is that in most any retail production facility, the "bottom line" is really the bottom line. Cost cutting leads to designs that are intended to just outlast any warranty. Only just. . . The serious profit is made through sourcing repair parts. Or replacements. . . Parts for older designs are getting hard to come by. The only real advice I can offer is to have contact kits or a spare relay in a plastic bag taped to the motor where it's easy to find.
.

 

[aliva]

Switching the coil is the best approach. I have a 5hp Gardner Denver compressor. I switch the contactor coil, it's been working for 30 years no issue. Never replaced a p switch or contactor.