Compressor won't fill past 5 bar

[trigg]

Right, who can help me..

Picked up a 100L Clarke Boxer 2 compressor, 3hp single phase 13amp, guess its 3/4 years old and looks like it has only had very light use. It starts fine, fills to about 5 bar and then stutters before throwing the 15 amp cut out. If I drop the pressure in the receiver it’ll start again just fine but the same thing will happen and it only ever reaches the same 5 ish bar.

• Non return valve replaced and working fine
• Pressure switch is fine
• I was away for a week so dropped the motor off at a local rewind place to give it the once over, they replaced both capacitors and bearings (although they didn’t run any of this past me just landed me with a bill..) Both new capacitors are in range on my multimeter
• Runs quite happily with no load
• Pump seems fine, it gets to 5 bar in less than two minutes which seems about right. Turns easily by hand including just after tripping the breaker. Oil has been changed with bog standard compressor oil
• I’ve checked all electrical connections and now wired the motor straight into mains and bypassed the thermal cut out just to be sure. No change..
• 238V at the plug

If anyone has any bright ideas or i’ve missed something obvious it would be much appreciated.

 

[voipio]

Is the motor unusually hot when it cuts out? Does the head gasket seem OK?

 

[trigg]

Not excessively hot, fan seems to be working fine. Haven't had the head off just the valve cover and all looked ok, guessing head gasket is ok as it doesn't seem slow to fill?

 

[Chippie]

Seems like a load issue…
So you have a 13a fuse in the plug, so you should be protected, ( but do check your upstream protection..) I’d be inclined to short out the 15amp cut out and try again….it could be weak…Do you have access to a clamp on ammeter? You could try reading the load current and let us know what it is…

 

[voipio]

The reed valves look rather gunky, and could probably do with a clean. Check the surfaces of the valves for pitting. The inlet port valves don't seem to be leaking.

 

[trigg]

13amp fuse in the plug yep. I've been through a couple of cut out switches and not seen any change but appreciate they don't always do well after a few trips.. I've got a clamp meter will have a look at load current tomorrow and report back. Cleaned up the exhaust valves after I took that photo and there didn't seem to be any pitting. Think it's worth head off and having a look?

 

[tom2207]

has anyone messed with the main pressure cut out switch ,,, is it arcing even.

 

[trigg]

Pressure switch is currently bypassed as I was trying to remove as many connections (failure points etc etc) as possible in the hope that I could get it to fill then work back from there. I did also fit the pressure switch earlier onto another compressor and it was fine.

 

[tom2207]

Pressure switch is currently bypassed as I was trying to remove as many connections (failure points etc etc) as possible in the hope that I could get it to fill then work back from there. I did also fit the pressure switch earlier onto another compressor and it was fine.

whats the oil like ,,, is it black and carbon ish , or has it maybe got bits in it .. its a teaser indeed

 

[trigg]

Yeah I changed the oil twice already just in case to make sure all the old stuff was gone.. haha. The first lot was a bit black and sludgy but to my eye just looked old, certainly no metal in there. Crank feels ok by hand too

 

[mike 109444]

Stick a pic up of your 15apm trip and I am sure someone will direct you to a more suitable one

 

[tom2207]

is it a motor rated trip

 

[trigg]

Appreciate it. Although as before the issue persists with the trip out the circuit

 

[tom2207]

i actually meant the mcb in the board

 

[trigg]

Yeah right. Consumer unit is Wylex pic attached - I imagine it's not motor rated but I figured relatively small volume 13a compressor should be fine? The issue started with the previous owner so I didn't really think about it.

 

[not done it yet]

I’m moderately surprised the motor is a two pole type. I would have expected a 4 pole motor to be fitted. What speed is the pump being run at?

 

[trigg]

Motor is 2850rpm and I guess visually from the pulleys the pump is running less than half that. Seems to be the originally supplied motor

 

[Jack_K]

The current measurement is what I want to see too. Measuring the voltage at the motor when running is also not a bad idea.

I’m moderately surprised the motor is a two pole type. I would have expected a 4 pole motor to be fitted. What speed is the pump being run at?

two pole is most common on compressors, at least any I have seen. I haven't actually seen any with 4 pole.

 

[not done it yet]

two pole is most common on compressors, at least any I have seen. I haven't actually seen any with 4 pole.

You’ve not seen mine, obviously. These pumps generally operate at around seven hundred rpm? Mine does, but that is a compound twin cylinder pump.

Yes, the direct-coupled ‘buzz-box’ cheap chinese compressors are more likely to be fitted with cheap 2 pole motors - but this was not a particularly cheap machine, I think.

If that pump is trying to run at 1400 rpm it will likely be loading up a 3HP motor as the pressure increases - particularly as it is a twin cylinder pump.

 

[MetalMonkey]

Majority of the belt drive units with that style of twin cyl pump seem to use a 2800 two pole motor, pumps run in the range of 1300 to 1800 rpm.

I checked my Sealey the other day and was comparing it to other brands - It has a 2830 rpm motor giving a pump speed of 1800 rpm. Something I'm intending on reducing to make it quieter.

Bigger three phase and two stage units tend to run pumps slower at the 850 - 1000 rpm range.

The V and W units run slow - My AIE "W" runs at 950 rpm.

So the motor speed seems about right for that style of unit.

What oil are you using, they typically take an SAE 30 or 40, and not being multigrade they can struggle to start in the colder weather, blowing fuses - but usually once they get going they are ok pumping up though.