The tale of a cheap(ish) little air compressor and partial teardown

[thefamilyman]

6/8 Bar is industry standard settings for an air compressor.
Most air tools are rated to operate at 6 Bar so use a filter/regulator set to 6 bar or what ever the air tool manufacture recommends.

look for an SMC regulator if you can but be aware of copies from china.

[Towger]

look for an SMC regulator if you can but be aware of copies from china.

Finding a good one at the right price which a not cheap chinese copy is always the trick.  [emoji57]

[Fraser]

I wanted a small 'PIG/Donkey' tank for my compressors so that I could carry around a pressurised reservoir easily for minor air needs. Garages used to have such on their forecourts for filling car tyres. They looked like a small propane cylinder and recharged when replaced on their stand.

I was very surprised at how expensive these small tanks can be. As much as a complete compressor in some cases. Next step... a search on ebay for faulty compressors    I immediately found one and it is perfect for my requirement. A low noise STANLEY 5ltr compact compressor with suspected dead motor. The price was right, as it included delivery, so I bought it. It looks to be in very good condition and who knows, I may be able to repair it  I noted teh small rocker switch used and wonder if that will be the issue, as with my other unit.  I want it for the air reservoir tank and associated valve gear, so no worries if the motor is toast. It also matches my STANLEY 24ltr compressor colour scheme 

More when I receive it.

Fraser

[Fraser]

Just looked up the spares list for the Stanley compact compressor. Most parts are available....... Except the motor/pump combination. It looks to use some form of axial direct driven pump as commonly found in automotive tyre pumps.

http://www.mtmc.co.uk/Spare-Parts/Stanley-Spare-Parts/Stanley-Compressors/Stanley-8213360SCR001-Type-REV-A-Compressor-Spare-Parts__p-240-12733944-12734901-94722.aspx

Fraser

[Fraser]

Looking at the parts diagram, I am wondering whether the pump motor on the little Stanley compressor is a 12V DC unit. If you look closely you will see an unidentified module that sits by the motor. A SMPSU ?  I can see no other use for such a module as STANLEY do not use any clever EMI filtration.

The use of a common COTS tyre inflation motor & pump combination is not beyond the realms of possibility as they can be very cheap.

It will be interesting to see when the unit arrives.

Fraser

[Fraser]

I see the little compressor is sold in Australia as a compact wall mount unit designed for portability and convenience.

http://m.supercheapauto.com.au/Product/Stanley-Wall-Mount-Air-Compressor-0-5HP-14LPM/342509

Fraser

[Towger]

The use of a common COTS tyre inflation motor & pump combination is not beyond the realms of possibility as they can be very cheap.

If it is the type of motor I am thinking of they tend to be nasty noisy and dont have a high cfm.

I took more of the filter and various connectors off mine, stuck them in the ultrasonic cleaner and added a few squrts of degreaser for good measure.   I should have known better... Now I have to replace half the o rings.

[Fraser]

@Towger,

I agree. If it is a standard car tyre compressor pump, it will be quite loud.

The Stanley specs say 83dBa and 55 ltr/min

http://www.screwfix.com/p/stanley-dn-8-5-4-5ltr-portable-air-compressor-240v/22374

I may just use it as a portable air reservoir.

Fraser

[Fraser]

There are several videos on YT.

Just look for Stanley 5ltr compressor



Time to full pressure from empty is 2 minuets 15 seconds and it may be noises but you cannot tell with YT videos as the camera mic can exaggerate the noise level unless a direct side by side comparison with a known noise level is demonstrated.

Having heard the pump, I am more convinced than ever that it is the same as used in decent quality tyre inflators.

Fraser

[Fraser]

The little Stanley 5ltr compressor arrived today I had it working within 10 minutes of arrival but it does have an issue as you will see.

The compressor does not use a 12V car tyre inflator pump but the pump is similar in appearance. The small PCB that I saw on the parts diagram is a simple 240V AC to DC converter using a bridge rectifier. The motor is rated at 230V DC and is a universal commutator type. The 3A 1.25" glass fuse on the AC to DC PCB had failed. I temporarily replaced it with a slightly more resilient 3A plugtop fuse that can better withstand inrush current.

The compressor fired up fine with this fuse fitted but as I always tell people, fuses do not fail for no reason. In this case the fuse had not failed in a manner associated with a massive over current event. It had slowly cooked and melted. A sure sign that it was placed under excessive continuous load over a period of time rather than a catastrophic overload event.

The compressor reached 7 BAR and I could hear an air leak. The unit should achieve around 8 BAR and then the pressure switch should cut the power to the motor. This never occurred. I had found my slow overload. The pressure switch could not operate as 8 BAR was never achieved. The motor ran for too long and the 3A fuse was thermally stressed by the long duration of the current through it and eventually failed with a wimper rather than a bang 

The air leak is being caused by the safety over pressure valve that starts venting at around 6.5 BAR. Way too low a pressure. If I hold the pressure relief valve closed, the compressor operates normally and cuts out at just out. BUT I need to check the pressure at which it is cutting out as it seems a little high to me. Time to check the specs and you tube videos of these running. It could be just inaccurate gauges as they do not tally with each other. Simple tests to perform so of no great concern. I have a spare pressure switch if needed. I will order a new safety pressure relief valve and they are cheap which is god news.

So I have a working mini compressor. It s a lot quieter than expected and the you Tube videos are nt fair to this little unit. Its noise levels are more than acceptable in the lab and it is a lot quieter then its bigger brother, the 24L direct drive compressor that I repaired at the beginning of this thread. The little 5L unit does nit have the harsh high frequency noise that I expected, ts more like my air brush compressor noise. Very nice.

Pictures follow.......

Fraser

[Fraser]

Well testing has confirmed a faulty safety pressure relief valve. It leaks above 7 BAR and occasionally blows out at 7.2 BAR. The compressor never reaches the 116 PSI required to activate the pressure switch.

If the relief valve is held closed the pressure increases correctly and the pressure switch activates at 116 PSI, as it should. I will fit a new relief valve and all should be well

With regard to the two pressure Gauges, the reservoir gauge reads slightly high by around 2 PSI, which is fine. The regulator output gauge reads way too high across the full operating range. This needs to be adjusted or a new one fitted. They are cheap enough. It has no PSI scale so I think I will just replace it.

Fraser

[Fraser]

The Lucar connectors attaching the wires to the power switch were the thinnest metal I have ever seen used for such. The Red wire Lucar connector was very loose and actually tore when I tried to tighten it up with pliers. Total junk and a fault liability. I re-terminated the wires with quality crimp Lucar connectors.

I have ordered a new output gauge of decent quality as the fitted gauge is also junk. A new safety relief valve is also en route to me. I chose the correct 8.8 BAR type for this compressor. I attach pictures of the gauge error and the replacement parts that I have ordered.

Would I recommend this compressor ? Quite frankly, NO !

It has its good points but the quality of the gauges, regulator, safety valve, electrical connectors and pump output pipework is left wanting.

I am pleased it cost me very little and I am able to address the more important failings for a few pounds so it is still worth doing.

My advice would be to pay a little more fr one of the neat 6L or  9L 'silent' compressors that use a similar pump to my 50L compressor. They have better build quality and a proper pressure switch. I attach a picture of such a unit.

Fraser

[Fraser]

The new parts arrived today 

I did not skimp on the gauge and the quality looks excellent. Far superior to the STANLEY original fitment.

The spring in the new safety pressure relief valve feels far more healthy when compared to the faulty valve.

Now to find time to fit the parts.

Fraser

[DTJ]

I picked up exactly the same unit from someones verge during junk week.

The fuse was blown, I didn't have the exact value and put in the next one up that I had - it runs fine. I've got a reminder tag on it to put the correct fuse in one day.
The pressure switch in mine works ok. I did notice quite a few sparks and arcs from the motor brushes.

Very noisy unit but small, portable and free.

[Fraser]

Hi DTJ,

The fuse gets cooked so it is worth checking the safety valve for leaks with a spray of soapy water. Mine was leaking so drably that it could be clearly heard. These units are definitely built down to a price. The Lucar connectors they used on the switch made the motor slightly stutter at times due to the poor connection they made. If yours are of similar poor quality I recommend fitting decent replacements.

As you say, if they are cheap enough, they are quite a convenient source of pressurised air. Mine is getting a full review and tidy up to improve its quality.

Interestingly, mine is not that noisy. It has a very acceptable lowish frequency buzz without the harshness found in electric drill motors or my other Stanley Compressor. The noise from the 24L Stanley is truly horrendous !

Fraser

[SeanB]

Not surprising they use an universal motor, as it is cheap and gives a very high torque for the mass. Downsides of course are a very short life compared to an induction motor, and the need for brushes really limits operating environment and motor lifetime. But as it uses less of that expensive CCA wire in the windings, and moulded ferrite magnets are very cheap in bulk, at least compared to casting a housing and putting in the laminated and cast in situ squirrel cage rotor, you can do it all with cold rolled sheet and a simple set of punching dies and a sheet metal roller.