An Air Compressor that Compresses Oil

[KavindaJD]

Hi all,

Reaching out to you guys that may know more about compressors than I do!

I recently purchased a second hand SIP 100L 3HP twin v style compressor. It had a fair bit of oil in the tank when I first drained it.
So I did a complete strip down and restored it - made new gaskets, replaced the rubber piston seals and got the scoring out of the bore with the help of a machine shop.

I've ran it for about 30 minutes since and it's very inefficient, taking about 7-9 minutes to reach its 9 bar cut-off. Air also seems to be coming out of the dipstick vent hole.
Stripped it down once again and found oil in the head with more scores on the cylinder:

The piston looks similar to the ones you get in oil free compressors with those rubber compression rings :

I'm now trying to hypothesise as to why this is happening. I can think of two things:
1. Piston misalignment with crank. I initially assembled the piston to the crank first then placed the cylinder over the piston. I've noticed a gap between the piston end and the retaining circlip.
2. Piston seal rubbing with an imperfect cylinder wall, trapping bits of metal in the oil and scoring the bore. Allowing oil to pass through over time.

Any ideas on where to go from here?

 

[mtt.tr]

How soft is your rubber,all the ones I've installed are more a soft plastic

 

[roofman]

In my eyes those type of compressor pumps are more of a use and throw away type..get yourself a cast iron pump and they service up better with a good honing and new rings.

 

[KavindaJD]

How soft is your rubber,all the ones I've installed are more a soft plastic

Yep, agree there. It not rubber - I think it's PTFE..

 

[8ob]

I am no compressorist but I would have thought PTFE rings would run in a chrome or nikasil bore , that bore looks hellishly rough.

Bob

 

[roofman]

I am no compressorist but I would have thought PTFE rings would run in a chrome or nikasil bore , that bore looks hellishly rough.

Bob

Yep..it looks like its been honed by the machine shop for the pretense it has iron rings

 

[gordon stephenson]

The "wobble piston" compressors I have dealt with had plastic/nylon "ring" spares were available, But you had to buy the full con-rod/piston unit

 

[KavindaJD]

Awesome, thanks for the input so far.
I’ll try and polish up the bored to get something somewhat functional whilst I look for a cast iron unit.

I was contemplating just hooking up a pump and motor to the existing 100L tank I have. It’s been kept in decent shape given how much oil had been sitting in there prior to me purchasing it!

 

[Wallace]

What bearings does the crankshaft and connecting rods have, are they open and require oil? The Thomas Wobl type I have worked on run with sealed roller bearings.

 

[KavindaJD]

What bearings does the crankshaft and connecting rods have, are they open and require oil? The Thomas Wobl type I have worked on run with sealed roller bearings.

Yep sealed roller bearings and requires oil..
The main crankshaft bearing is open.

 

[KavindaJD]

So I've managed to pick up this tank of a compressor on the bay of fleas after @roofman suggested I go cast iron:

I believe it's a Stenhøj K66A pump from this video:

The pump on mine reads "100700" which is the same as the one presented in the video.
There is a plate on the pump with a serial number from HPC with an RPM figure.

The motor is single phase and has this note on it:

I assume the starter is the white box on the pump. Must I run a fused isolator for this or can I get away without one?

Any ideas on how I could go about finding the exact model number for the pump (there is a K66A, K66B and other pumps that look very similar)?

Thanks for all the help so far!

 

[carbon]

The motor has a current rating of 15 amps when at full load, so maybe a little high for a standard 13amp plug

 

[roofman]

The motor has a current rating of 15 amps when at full load, so maybe a little high for a standard 13amp plug

Same 2.2Kw motor that's on most of the industrial pressure washers, i know compressors can be power hungry as they build pressure but tbh i have never had a problem myself with a 15A motor on a 13A plug.

 

[carbon]

Same 2.2Kw motor that's on most of the industrial pressure washers

Nearly all the pressure washer motors of 2.2kw I see have a 13amp rating

 

[roofman]

Nearly all the pressure washer motors of 2.2kw I see have a 13amp rating

Is that the Italian made ones that vibrate that bad you cant switch them over to a lathe or big pillar drill

 

[carbon]

A lot of the motors are designed for direct mounting of pumps the the end of the motor to make a smaller size package. These motors usually only have one bearing at the fan end and rely on the two bearings in the pump for alignment of the rotor as such they are limited to that application only as they don't have a male shaft to fit a pulley or coupling. Some are male shafted and as such would be suitable for use in other applications but i've never had any problems with motors vibrating. There is one three phase motor (5.5kw) that's used in pressure washers that has a smaller frame size than it would normally have as a standard motor, its physically the same size as a standard 4kw motor so lends itself for fitting in smaller spaces. I use one of these on an extractor with vfd without any issues. I very seldom see any motors that spin at 2800 rpm

 

[KavindaJD]

The Stenhøj pump seems to be better than expected.
However, I turned the pulley by hand a few times and noticed air coming out of the breather and suspected the worst - bad rings or bore.

I started stripping the pump and to my surprise, there seemed nothing out of whack; especially for a 1980's pump that hasn't seen an oil change.
The piston rings have a little wear to them on the edges but I can still see the original honing marks on the cylinder:

My questions are:
1. Is it normal to have some air being pushed into the crankcase and out of the breather?
2. Does this need a ring job and honing?

The bearings don't seem bad, so looks like I need to regasket and do a thorough clean for the time being.

 

[mtt.tr]

The Stenhøj pump seems to be better than expected.
However, I turned the pulley by hand a few times and noticed air coming out of the breather and suspected the worst - bad rings or bore.

I started stripping the pump and to my surprise, there seemed nothing out of whack; especially for a 1980's pump that hasn't seen an oil change.
The piston rings have a little wear to them on the edges but I can still see the original honing marks on the cylinder:

View attachment 321286 View attachment 321287

My questions are:
1. Is it normal to have some air being pushed into the crankcase and out of the breather?
2. Does this need a ring job and honing?

The bearings don't seem bad, so looks like I need to regasket and do a thorough clean for the time being.

Not loads of air but some as you are changing the crank case volume when the pistons go up and down

I'd run it and see if it builds pressure

funny how hpc have changed through the years some of their early screws are crap reliable but no thought to servicing the modern ones are a dream

 

[KavindaJD]

Hi all,

Hope everyone has had a great start to the new year!

I've only just got the wiring upgraded in my garage to 32A and had a chance to try out the motor.
The motor itself is wired via the starter to a 16A breaker - and it trips every time..

There was a little pink slip inside the motor wiring housing which has this diagram - Diag. 60 from the nameplate:

The table on the right lists the poles to be connected via metal links. I'm assuming I'm on the "LOW" setting for 230V - I've verified the links have been connected correctly.
Resistances of the three windings are about 5 ohms with no shorts to ground as far as I can tell.

I'm not a sparky but connecting U1 to U3 surely produces a short circuit from Line to Neutral via U4?

 

[carbon]

I'm not a sparky but connecting U1 to U3 surely produces a short circuit from Line to Neutral via U4?

No you then have two windings connected between live and neutral in parallel and an additional one with a capacitor in series when the motor is stationary