clarke se18c200 - motor slowing

[stuartsports05051985]

hi guys, wonder if anyone can help here.
I saved up last year for one of these 4HP clarke compressors as an upgrade for my 12 year old clarke 1.5HP one which was faultless.
The new one ran great for around 13 months, then one day, the motor/pump started slowing, dropping off maybe 10% of its normal RPM. this was intermittent at first then, regular. wasnt always just a first run either. It got so bad that the rpm was dropping to maybe 30% of its normal, it would sometimes pick back up and slow. I managed to get a replacement motor, and when i fitted it, it ran like new again, until about 3 weeks later, the exact same issue has started. starts off 100%, 10 to 20 secs in, it drops off like its going to stall, then slowly picks up. then each subsequent run is different.

Any help or ideas to check would be appreciated.

Thanks

 

[rtbcomp]

Can you connect a voltmeter to where the motor connects to the pressure switch? If the voltage drops significantly when the motor slows you may have an intermittent bad connection somewhere. Look for signs of the contacts overheating in the pressure switch.

Is it single or three phase?

 

[daleyd]

Are the belts slipping? Motor may be Ok and just the pump slowing.

 

[stuartsports05051985]

Can you connect a voltmeter to where the motor connects to the pressure switch? If the voltage drops significantly when the motor slows you may have an intermittent bad connection somewhere. Look for signs of the contacts overheating in the pressure switch.

Is it single or three phase?

hi, voltage stays constant, we checked the supply from house, right the way back to garage etc. single phase motor also

 

[stuartsports05051985]

Are the belts slipping? Motor may be Ok and just the pump slowing.

hi, no belt seems to be tensioned ok

 

[daleyd]

hi, no belt seems to be tensioned ok

Can be deceiving though, especially if they are bottoming out on the pulleys, may be worth a try at some belt dressing spray as a quick/cheap test.

Do you have access to a tacho to measure the motor/pulley rpm?

 

[stuartsports05051985]

What CSA is the supply cable?
How long is the supply cable run?
Are you in town or on a pole transformer?

Could be the socket possibly has a bad connection, your using undersized cabling, the oil in the pump is thickening with the cold to the extent its slowing the motor and possibly other possibilities...

i think its 10mm from the house to garage, which is around 15m length. then i think 6mm from the garage consumer unit to compressor which is less than 1m distance. Was fine for over a year with this set up. We are in a town. Had a different electrician check all the circuitry out and all seemed fine. Also, fitting the new motor resolved the problem for a short while.

The oil is the only thing ive not changed. But wouldnt explain why changing the motor resolved the problem?

 

[stuartsports05051985]

Can be deceiving though, especially if they are bottoming out on the pulleys, may be worth a try at some belt dressing spray as a quick/cheap test.

Do you have access to a tacho to measure the motor/pulley rpm?

no unfortunately,

 

[daleyd]

http://www.ebay.co.uk/itm/Digital-L...924259?hash=item1c64a9a723:g:SVsAAOSwubRXMZwx

something like this may be useful for diagnosing stuff like this, not sure how accurate they are but all your after is a comparison between the motor and pump. I used to use one a lot when I was a field service tech on industrial dryers and suchlike, used to do a lot with fans etc and it was an invaluable tool for problems like this.

 

[stuartsports05051985]

does the motor slow down when there isn't load on it? i.e. when pump disconnected?

havent tried that, will do tomorrow

 

[rtbcomp]

Can be deceiving though, especially if they are bottoming out on the pulleys, ...

+1 this caught me out on a compressor.

When it starts to slow has the pressure increased beyond the cut-off point, but the switch hasn't opened?

 

[stuartsports05051985]

+1 this caught me out on a compressor.

When it starts to slow has the pressure increased beyond the cut-off point, but the switch hasn't opened?

no, its usually about 20% of the way thru its cycle, it starts to pick back up nearer the end

 

[Mee]

Has it got an inline starter as often these can become troublesome?

 

[stuartsports05051985]

ok, so it seems the issue was the belt tension. I tightened it and have been running it all day and the issue is no longer apparent. so am gonna get a new belt ordered and do an oil change shortly which should help

 

[rtbcomp]

Thanks for the update - it all adds to the knowledge base.