Atlas Copco Compressor problem

[rickyn]

Hi All
Is there anyone here who can help me ?

A few weeks back i made the 150 mile round trip to where my compressor had been stored for the last twenty years, and amazingly when plugged in it hadnt seized and fired right up.

This was in full working order when it went into storage in 1993, so borrowed a van and i went back this weekend and collected it. So tonight i fitted a new power lead as it was falling to peices, got it into position and connected it up to the water traps and wall take off points. Once it was air tight i ran it gingerly up to full tank pressure without issue, and the motor turns off as it should at about 115 psi, however when the pressure drops in the line to the point the compressor motor needs to chime in again, as it goes to do it pops the 13 amp fuse in the plug. Its done it every time tonight so the lay up has clearly caused a problem.

Im loathe to throw it after all this effort but can anyone offer any pointers what it could be and if i can fix it ? Its an Atlas Copco in case it makes a diference?

 

[brightspark]

Hi All
Is there anyone here who can help me ?

A few weeks back i made the 150 mile round trip to where my compressor had been stored for the last twenty years, and amazingly when plugged in it hadnt seized and fired right up.

This was in full working order when it went into storage in 1993, so borrowed a van and i went back this weekend and collected it. So tonight i fitted a new power lead as it was falling to peices, got it into position and connected it up to the water traps and wall take off points. Once it was air tight i ran it gingerly up to full tank pressure without issue, and the motor turns off as it should at about 115 psi, however when the pressure drops in the line to the point the compressor motor needs to chime in again, as it goes to do it pops the 13 amp fuse in the plug. Its done it every time tonight so the lay up has clearly caused a problem.

Im loathe to throw it after all this effort but can anyone offer any pointers what it could be and if i can fix it ? Its an Atlas Copco in case it makes a diference?

it will be the starting current under load will pop the fuse easily. has it got an unloader valve on it and is it working even so 13 amp is a bit small 16 or 20 amp would be better. also make sure it has a decent lead on it and not too long if it isnt

 

[Robotstar5]

I'd be worried about rust forming in the base of the receiver after 20 years storage, might be a bit thin!

 

[rickyn]

it will be the starting current under load will pop the fuse easily. has it got an unloader valve on it and is it working even so 13 amp is a bit small 16 or 20 amp would be better. also make sure it has a decent lead on it and not too long if it isnt

Unloader valve ? And where would i get a heavier fuse ?
Thanks for the replys

 

[rickyn]

I'd be worried about rust forming in the base of the receiver after 20 years storage, might be a bit thin!

Dont say that, it was in my thoughts as well. I have had this since new and it was fully drained when i left it, but surely theres older compressors than this knocking around and in use ?

 

[brightspark]

Unloader valve ? And where would i get a heavier fuse ?
Thanks for the replys

when it cuts out do u hear a hiss of air out of the cutout switch it may have one it may not it emptys the pipe of pressure between the pump and tank making it easier for the motor to start under load the comp would need wiring in to a 16 amp feed as 13 amp is the biggest fuse u can get in a plug

 

[squazy84]

ive a 1954 compressor,wasn't drained for the best part of 20 years,astonishingly little rust and it had loads of water in it,for some reason the rust was only surface,my money would be on the unloader valve

 

[rickyn]

Ok so when it reaches pressure and cuts out i should hear a hissing if the valve is working properly ? If thats correct i will specifically check that tommorow night.

 

[madkayaker]

ive a 1954 compressor,wasn't drained for the best part of 20 years,astonishingly little rust and it had loads of water in it,for some reason the rust was only surface,my money would be on the unloader valve

we have similar at work but is it made from 3/8 steel

 

[normspanners]

The other thing people forget is that the oil can thicken with age and thick oil causes a massive increase in starting load.
Also caps can dry out and not be as efficient for starting, when you started it at the other place the mains could have been a slightly higher voltage than your present location, which again would have aided in cranking power.

 

[adamsmitqc]

I had a similar problem a while back on my 23 year old compressor. It was unloading fine but would repeatably pop the fuse when trying to cut back in to top up the receiver pressure.

I traced the problem to the NRV (non return valve) which is located at the end of the discharge line before it enters the receiver. The NRV had degraded over time so as the unloader valve vented off the discharge line, over time pressure from the receiver was passing back into the discharge line and consequently the head of the compressor. Therefore, the compressor was starting against a head of pressure and causing the starting current to pop the fuses.

Cost a couple of quid for a new spring and diaphragm for the NRV.

 

[rickyn]

I ran it up on my last fuse last night and when the motor cut i could hear and feel a hissing from a pipe that runs from the switch to the finned object on the front left of the image. So it seems it is unloading the line ok.

Im not at all sure what hp/cfm/tank size i have but heres a pic. I have still yet to clean it up after its layup
The motor is made by Leroy- Somer and its says it rated at 1445 litres/min. Surely this cant be right though as thats over 50 cfm isnt it ?

 

[brightspark]

that rating will probably be the motor speed rpm

 

[rickyn]

That would make more sense, i suspect its about 14 cfm.

 

[brightspark]

if the motor is 2.2kw it is a 3 hp motor thats whats normaly fitted to a 14cfm pump

 

[rickyn]

Ok tried again tonight with a connection to a higher amperage plug, it still wont restart to refill the partially full cylinder. It tries to but the engine wont fire up.

So, if you look at the image i posted of the unit, from the switch there are two pipes coming off, one to the tank gauge, the other goes off left to that finned unit. This pipe at the switch end has a bleed hole, when the tanks full and it cuts out, immediately air starts escaping via this bleed hole until the tank empties enough for the motor to chime in again, which it doesnt. So can i take any of this apart to check anything ?

 

[rickyn]

I had a similar problem a while back on my 23 year old compressor. It was unloading fine but would repeatably pop the fuse when trying to cut back in to top up the receiver pressure.

I traced the problem to the NRV (non return valve) which is located at the end of the discharge line before it enters the receiver. The NRV had degraded over time so as the unloader valve vented off the discharge line, over time pressure from the receiver was passing back into the discharge line and consequently the head of the compressor. Therefore, the compressor was starting against a head of pressure and causing the starting current to pop the fuses.

Cost a couple of quid for a new spring and diaphragm for the NRV.

Wonder if mine has the same setup ?

 

[adamsmitqc]

Some clearer pictures would help, some of where the air enters the receiver and also closer one of the pressure switch.

 

[adamsmitqc]

Ok tried again tonight with a connection to a higher amperage plug, it still wont restart to refill the partially full cylinder. It tries to but the engine wont fire up.

So, if you look at the image i posted of the unit, from the switch there are two pipes coming off, one to the tank gauge, the other goes off left to that finned unit. This pipe at the switch end has a bleed hole, when the tanks full and it cuts out, immediately air starts escaping via this bleed hole until the tank empties enough for the motor to chime in again, which it doesnt. So can i take any of this apart to check anything ?

When the motor cuts out, the unloader shouldn't be venting the receiver pressure at all, it should only empty the discharge line between the compressor head and an NRV. If it is venting down and you are seeing a reduction in receiver pressure then I would assume that the problem lies with an NRV as previously mentioned.

It's hard to see the exact setup from the picture but I think that within the finned block you mention you will find a valve.

 

[rickyn]

This really makes sense, as the reciever is constantly filling the pipe with the unloader in it instead off closing the curcuit. I will add more pics tonight, if you chaps would be good enough to have a look and give me an idea what to start stripping to find the valve it would be much appreaciated.