Compressor won't fill past 5 bar

[trigg]

Thanks both, some quick math on the pulleys has me at about 1350 for the pump which seems the right ball park, and as before no reason to suspect pulleys or motors have been swapped out. Good to check nonetheless.

I've had the clamp meter on it and it definitely looks like a load issue across the range, meter reads 12/13a when it settles down after startup, which climbs to 15/16a when it starts to stutter. I would guess normal range should be more like 10-13a rather than 13-16?

I quickly retested both capacitors to double check, with the 200-250 reading at 215, 213, 214 and the 50 showing three readings of 49.3.

Oil is a cheap SIP compressor oil (Advanced Piston Compressor Oil I think its called), it struggles a little on cold start but does get going fine.

Feel like I've ticked most of the electrical boxes but equally with new bearings in the motor and the pump feeling ok by hand a mechanical issue isn't obvious... I guess I could give the pump a full strip to be sure?

 

[Kram]

Just to check the details... It is not blowing the plug fuse or tripping the MCB, only the CB built into the compressor is tripping?

I would stick a clamp meter on it and bypass the trip to see if it then fills up to pressure or trips the MCB/fuse while keeping an eye on the clamp.

 

[trigg]

Correct. It obviously slows and starts to stutter before throwing the cut out which is between live in and the run cap (assume the 50 is the run cap..). When I bypass this and go live straight to cap it does the same thing and then blows the 13amp plug fuse. I'll double check this now with the clamp meter.

 

[Kram]

Ok then that rules out the 15a trip being faulty - it takes a lot more than 13A to blow a fresh 13A fuse in a short time frame, so perhaps best not to repeat the test.

I would get the head off and check the piston and bore. It may have oil vatnish or scoring or some reason for high friction which is over loading the motor.

 

[6ply]

Motor data plate states "termically connected" ????? Not sure what that means! Does that mean the motor itself has a thermal cutout? I'm wondering that as it is a cheap S3 rated motor with a 50% duty cycle. Such motors get hot when pushed hard.

 

[dave h 2]

My 3hp pump runs constant at 10A and starts at 20A peak so it does look like an overload .
Looks like one pot is overheating as one reed is more coked up than the other. I would wonder about the pump pulley being on backwards except theres more amps being drawn than normal when cold.
It might the coked reed sticking closed when it warms up

 

[trigg]

Ok head off and nothing too conclusive to my eyes, let me know if you think otherwise. Gasket was not in a hurry to let the thing come off.. I did clean the exhaust reeds earlier with no change and the actual reeds weren't so bad under the coked up limit plate things.

Dave what do you mean by pump pulley on backwards? I did some thinking about overheating but if you cycle a few fills emptying the tank in between the cut off doesn't seem to happen any earlier - it may be that it has enough time to cool but i figured you would get some compounding of heat build up.

 

[bricol]

Simple things first (might be a bit late looking at the photos . .) - is it actually stopping at 5 bar . . . or is the gauge damaged?

 

[trigg]

I'm not against it being something simple at this stage.. In fact, that would make me happy.. Yes definitely 5 bar, have tested the gauge.

 

[Kram]

If the reeds were leaking, the compressor would be fighting tank pressure for the whole stroke rather than pressure just at the top of stroke?

I suggest stripping it further to inspect the bores and crank bearings.

 

[Chippie]

Shorted turns in the motor? Although youve had the motor tested?

 

[MetalMonkey]

Silly question, but you said it turns freely by hand - was that before or after it had cut out at the 5 bar pressure?
I'm wondering if it is binding up when it gets hot.

 

[carbon]

I've had the clamp meter on it and it definitely looks like a load issue across the range, meter reads 12/13a when it settles down after startup, which climbs to 15/16a when it starts to stutter

If after startup is with the receiver empty then this is current is to high. The current should only be at 13amp or a little lower when it gets nearer the shut off pressure.

Measure the current of the motor with the belt to the pump removed so the motor has no load.

 

[trigg]

Motor has been tested yes, I did do a quick check on the windings with the multimeter just in case and seemed about right without knowing/having specs to hand.

Turns over fine by hand after cut out, hard to get to it before the pressure relief goes so not sure about that but it definitely doesn't appear to be hot seizing etc. It also doesn't seem excessively hot to me.

@carbon I did another test from empty and it was more like 10amps after start, although agreed this seems to be where the problem is manifesting.. I'll get the meter back on it but it runs quite happily with no load.

 

[trigg]

With no load the motor is pulling just over 2amps.

 

[dobbslc]

Have you checked the pastle in the non return valve?
Check the rubber as well as the metal part it seals to.
The fact everything else checks out ok but it's still tripping once the tank has a good bit of back pressure makes me think something isn't right here.
I've had trouble with my compressor and @JOEPRO said to loosen the union on the pipe from the non return valve to the cylinder head and listen for air, it should not leak. Don't undo the wrong side of the valve !!!
Joe correct me if I'm wrong here.

 

[Chippie]

With no load the motor is pulling just over 2amps.

Get a lump of 4*2 and put it up against the motor pulley while it’s running with the ammeter on it, then see what readings you get….

 

[dave h 2]

Ok head off and nothing too conclusive to my eyes, let me know if you think otherwise. Gasket was not in a hurry to let the thing come off.. I did clean the exhaust reeds earlier with no change and the actual reeds weren't so bad under the coked up limit plate things.

Dave what do you mean by pump pulley on backwards? I did some thinking about overheating but if you cycle a few fills emptying the tank in between the cut off doesn't seem to happen any earlier - it may be that it has enough time to cool but i figured you would get some compounding of heat build up.

If the pump pulley goes on backwards it sucks air past the pump cylinder, which is much less effective. Just ensure that the draft blows over the fins.

 

[trigg]

Thanks @dobbslc makes sense but definitely no leaks, replace the non return valve is one of the first things I did because I wasn't sure about it. It's working fine and the receiver will hold pressure even with the cylinder head disconnected.

@Chippie sounds good. What exactly am I looking for/how much resistance am I trying to apply with the 2x4? If we already know its fine running with no load and struggling with the pump load at 5 bar am I just looking for another reference?

 

[trigg]

@dave h 2 gotcha, yep definitely blowing.