What is this buzzing switch

[festive]

I bought a jun air compressor which is fitted with this switch, looks like a double pole isolator to me, but I could be wrong.

Anyway with the metal cover on the front it buzzes until you physically push the switch down it stops vibrating which is guess is the 50hz mains oscillation causing the vibration?

Any ideas how i stop it, can i take this unit apart, any ideas of a replacement unit i can fit?

//media.diynot.com/22000_21436_82428_33630177_thumb.jpg

 

[RF Lighting]

Any chance of an in focus picture?

It's possibly a contactor which it's normal for them to hum especially as they get older. If it's just an isolator then something may be amiss.

 

[Taylortwocities]

The pic is too small to see what it is.

Follow the upload instructions //www.diynot.com/forums/viewtopic.php?t=129539
and we'll be better able to help.

 

[ericmark]

The switch

Untitled

• festive
• 9 Sep 2014
• 1

would seem to be a motor overload which today would look more like this

it is called a "Motor Protection Circuit Breakers" cost around £30 but likely you would need an enclosure as well. Can't see details on your picture. The bit which seems to say "HEATER Hdg 61 switch off before removing" was selected to match run load of motor there were charts to select correct value but I don't recognise the make. Maybe Dorman Smith.

 

[festive]

Ok i have taken a larger pic, sorry not adjusted orientation.

 

[festive]

OK i think ive answered my question, well, thanks to Jun AIR uk, it seems this switch isn't standard.
I can only assume it was some sort of added requirement for this to operate in the school it was removed from, does that make sense?

If so im going to remove it and just leave the mains operated air pressure switch as the main switch.

cheers.

 

[ban-all-sheds]

If it's just a switch why does it make a noise and why does the lever say "RESET"?

 

[flyingsparks]

It's an overload to protect the motor. As Eric says its pretty old school, and the modern ones look like the one Eric pictured. You shouldn't bypass it, if you want to replace it with a new one you need to know the Full Load Current (FLC) of the motor (it should be on the motor plate) and get an overload to match that.
Without the overload you risk the motor overheating and causing damage.

 

[ericmark]

Most compressors de-load to re-start motor although some the motor runs all the time.

The de-load is often a pneumatic valve which lifts the intake valve in the cylinder until the motor has had chance to get to full speed. Should the outlet valve leak the cylinder can become pressurised and as a result the pneumatic valve can't lift the inlet valve as there is too much pressure behind it.

Should this happen the motor will stall and unless some thing disconnects the motor it will burn out. Using a motor overload is the best way to guard against the valves leaking and sticking and causing the motor to stall and burn out.

Some use motor rated fuses but if it happens this can work out expensive. If the compressor is being used then the time between switching off and back on is short likely not enough to allow any leaked air to pressurise the cylinder. And on first switch on there is no air in receiver so again no problem. But where it's on stand-by and not being used much this problem can arise and it is likely this will happen when your not there to see it happen.

The first time it happened to me it took me ages to find out the fault which resulted in many fuses blowing before I found it. I to cure the problem re-wired the compressor so instead of opening valve on star it allowed it to close on delta so pressure could not build up as held open while compressor is not running. But I would not think your compressor is star/delta start and of course there are other things as well which can stop the motor starting so a motor overload is a good idea.

Where a contactor is used the overload is often part of the contactor the one you have and the replacement I show is stand alone. The old one you have had a range of heaters the new one much simpler it has a dial with a range so you can set it to match motor without having to buy the matching heater.

I think old one may be General Electric this chart allows heater selection. I am not sure if it's a 198 Ph or HP 861 if the latter then likely for a 0.861 horse power motor. These are very old units and the unit may be simply worn out or it could be it's on the point of tripping which may point to a bearing or other faulty part.

 

[festive]

Thanks all for your help so far, so I need a new unit, does this clarify what I need as a newer version? Ive taken a shot of the side of this switch, has rating info:

 

[ericmark]

Without a chart showing 198 Ph or HP 861 which ever way it's read not a clue. I would look at the motor for a rating plate.

Are you setting up a museum? I looked for details of the MEM 2SPS starter it would seem these are 1970's era and were used on small hacksaws and the like.

I was unable to find a picture of the inside but I remember many starters of that time used dash pots filled with oil.

The overload was often bought separate to the starter and what it says on the base may not be what it's configured to do. 2.4 HP or 1.8 kW is the size of the contactor the overload needs selecting to match motor.

 

[bernardgreen]

The "no volt release" fuction is also important. It means that if there is a break in the power supply then the switch will open and the motor will be stopped. The switch will remain open until a machine operator can check the equipment is safe before resetting the switch and restarting the motor.

This is an important safety feature with a motor driving a compressor