The Stovebolt Site Forums The Shop Area The Tool Chest Reliable compressor pressure switch

I have a 5HP ( 5 real HP, 220V 30A) motor that seems to eat pressure switches. The ones I buy are 240V 50A rated but for the second year in a row the replacement switch has flaked out.

If I tap the switch I can see the contacts arc, and the motor turn for a few rotations but the switch never trips.

The pump has a working unloader and everything else is fine electrically/mechanically.

Is there something that needs adjusting/cleaning?

Short of fixing the one I have, what is a good brand of switch for this motor?

Should I get a magnetic starter?

A motor can draw several times the name plate amps while starting and even an unloaded compressor takes a good effort to start. Some literature suggest in the neighborhood of 5 or 7 times name plate amps!

I'd solve the problem with a motor starter rated for the size/amps of your motor.
May be able to clean the points on the old pressure switch and use it with success for "pilot duty" controlling the new motor starter.

Also, might be worth checking the condition of the starting capacitors (not sure how) but I can imagine if they were not doing their job it'd have serious starting amps.

Grigg

The pressure switch is the real issue.. when I drain the tank to <90 PSI (low set point) the pressure switch does not click on... and the voltmeter tells the same story.. the contacts are open.

I don't think a mag starter would help that.. would it?

That does sound like a problem. I misunderstood the spark and motor trying to start part...

In any case a magnetic motor starter may solve the problem of killing pressure switches.

I equipped my compressors with surplus electrical stuff including Square D pressure switches from eBay at quite reasonable prices. May take some research and understanding to ensure you get what you need.

Grigg

Pressure switches just aren't really built to start a compressor motor of 5 hp on 220v single phase. All of my compressors have magnetic starters. Furnas, Siemens and Square D are good ones, but they really need magnetic starter.

When the pressure switch does work (after I tap it) there is an arc.. but the motor kicks on no issues.

My main concern is that the pressure switch is not cycling. I've had the emergency release valve go off more than once (that is a scary sound)so when I do run the compressor I monitor the run time and tank pressure closely.

The last two pressure switches were name brand (about $70 each) and lasted less than a year.

Is there any maintenance to the pressure switches? I haven't taken it off the receiver yet... I was hoping to be able to fix it without removing everything.

I'm not aware of any maintenance requirements for the pressure switches. If adjustable has it been adjusted outside of it's optimal/design range. Has vibration changed the adjustment?

For operating a motor starter I have one of these on my compressor, it has given no trouble, is adjustable, and seems more rugged than some switches.
http://www.ebay.com/itm/Square-D-Pr..._DefaultDomain_0&hash=item23442f2141

After reading all this, my first question is where are you purchasing these switches? The very same place? Try using a different, more mainstream vendor. As Grigg eludes to, use American parts. My compressors are far higher HP and output and I have zero problems with this issue.. but I make sure to use American parts with a good warranty. Not sure what we will do when there are no American manufacturers left. But meanwhile, if they are in America, I know where they live. They KNOW I know where they live and they behave accordingly. Its just good business to provide local consumers with solid products. The cost is irrelevant to a point.

Lastly, and something to check is, what is the exact power coming in to the building? 240 +/- what? If you have serious power fluctuations that could be a problem. Power is a derivative of voltage AND current. I think the power company usually will check that for free. Are there other pieces of machinery drawing down then spiking up the voltage? Sometimes you have to live with who is sharing power in the same building (or circuit), other times, the power company put you on the same circuit (even though you have a small outbuilding behind your house) as some voltage/current sucking company down the line. Also, contrary to the weekend warriors of electricity, the black wire needs to correspond with the black wire throughout. Getting wires crossed in AC still works, but it introduces these very issues. I never trust myself to decide this. I call the electrician and sure enough, I get bitched out for crossing the wires now and then. Hope this helps. If I take your posts literally, seems you may have an anomaly associated with fluctuating power or something out of your control.

Think about it.. did the compressor work with the electricals it came with as advertised? Adding magnetic starters, etc to something that wasnt designed for it seems problematic. If the engineering of the product was good in the first place, it has to do with other factors maybe?

Basic electrical wire colors for buildings. Black, Hot. White, Return. Green, Ground. Red, Hot. Notice, White, Return, is NOT Green, Ground. Typical 240 Volt is not 240 Volt. It is 120, two phase with a common return. If you measure from Black to White, you will see 120 Volts. If you measure from Red to White you will see 120 Volts. If you measure from Black to Red, you will see 240 Volts. If you have a good system, measure from Green to White. You should see 0 Volts. If you have 3 phase power, well then all bets are off. More than 1 way to get delta power. Call an electrician.

It's not uncommon for larger equipment t
o need a magnetic starter added. I have also seen 3 phase equipment used with single phase power using a magnetic starter and phase converter.

I had the exact same issue. Mag starter took care of it - no more issues.

Good Luck

Update...

Looks like a critter (stinkbug?) tried to make it their home and was jamming up the works.

Took apart the switch and basically cleaned and put a dab of grease the contact pivot point. Action is much smoother.

Contacts were in good shape.

If the pressure switch never turns on neither will a mag starter. I guess should have left the cover on the switch after I adjusted the set points.

That's funny. I fixed a pressure switch on a friends compressor a month or two ago, fried stinkbug in the contacts.

Glad you got it sorted out.

Grigg

I have had similar problem with finding a quality replacement switch and not paying an arm and leg for one. Price one from Ingerssol Rand, for example, and they are over $80 if I recall. Similar Square D switch from local well-stocked hardware store was closer to $30. Took me a while to find out they carried them, as they were not shelved, you had to ask at their electrical supply desk.

I just got myself into the habit of unplugging the compressor at the outlet.
have had two issues that did not help the switch out due to being plugged in. One I am pretty sure was a lightning hit that did fry an IR switch, the other was an air line that popped off so the machine ran (for hours??) until the thermal switch on the motor turned it off and I think all the heat did the switch ill will.

At any rate, since I unplug it when I leave the shop I have had no pressure switch issues.