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Old 18th Aug 2020, 3:09 pm   #1
Uncle Bulgaria
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Default ITT air compressor servicing

I've seen a couple of threads on compressors, with their uses in cleaning and finishing radios so I hope this isn't too far off the forum topic! It is a vintage compressor after all...

I've been given this, in a marvellous gold, and wondered if anyone had any advice for servicing it. I can't find a model number, and the only identifying feature is the 'ITT' on the fan guard.

I can't find a lubricant drain or filling cap, so wonder if it's oil-less. There is no petcock for draining the tank, so I think I will drill and tap the lower large plug for this purpose. I haven't been able to shift the plug yet with my biggest spanner (it's about 1 1/2"/38mm) to see if there's any water in the tank.

I've got one of the cylinder covers off and there doesn't appear to be any lubricant in the cylinder, just two loose rings on the piston. The rear end of the piston is open to the air.
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Old 18th Aug 2020, 4:09 pm   #2
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Default Re: ITT air compressor servicing

There are two output ports and the one without a gauge on it is angled and will most likely have a pickup tube on the inside to drive any water out by air pressure when the valve is open.
Those big bungs look like they are there for access to spray paint the inside of the tank for rust proofing.
There ought to be some sort of oil point on it.
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Old 18th Aug 2020, 5:03 pm   #3
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Default Re: ITT air compressor servicing

Quote:
Originally Posted by Uncle Bulgaria View Post
I've seen a couple of threads on compressors, with their uses in cleaning and finishing radios so I hope this isn't too far off the forum topic! It is a vintage compressor after all...
Whether or not it's on topic for us, and for how long it continues, depends entirely on subsequent posts.
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Old 18th Aug 2020, 8:12 pm   #4
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Default Re: ITT air compressor servicing

It looks like the sort with an off centre rotor with slats set in. As it rotates, centrifugal force throws the slats out to the periphery, just like the NSU Wankel engines. Slats may be made of Tufnol or similar. Should not require lubrication as I recall.
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Old 18th Aug 2020, 8:23 pm   #5
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Default Re: ITT air compressor servicing

The stubbiness of the cylinder head (or heads) suggest a diaphragm type compressor rather like the Thomas Industries designs using a rubber diaphragm that distorts against the action of the con-rod. Typically they deliver around 40psi and require little maintenance having simple flap valves, ideal for blowing out radios.
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Old 18th Aug 2020, 8:30 pm   #6
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Default Re: ITT air compressor servicing

Looks like the pumps used on waveguide pressurisation systems. Maintenance free presumably. If it hasn't got it, it doesn't need it.
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Old 18th Aug 2020, 8:59 pm   #7
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Default Re: ITT air compressor servicing

That's very helpful. Thank you for all the responses. I've got an impact driver on the other cylinder cover and I'm continuing to strip it down. I've been wary of being doused in ancient oil, so if it seems likely it's an oil-free type that takes a weight off!

I was hoping it was suitable for an airbrush as that part of chassis restoration I've not delved into yet. I've heard horror stories of compressors exploding though, so thought the hive mind here was rather worthwhile consulting before I do anything silly. 'Compressed air' sounds so innocent, but it can be a real danger.
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Old 18th Aug 2020, 10:47 pm   #8
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Default Re: ITT air compressor servicing

That type of machine would be OK for an airbrush, not enough for a spray gun. For blowing things out, the pressure will be a bit limited.

ITT branding is interesting. Maybe used with a desiccant unit to supply dry air at modest pressure to waveguide or coax systems.

It seems to have lost one fan blade, or is the picture very distorted?

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Old 19th Aug 2020, 12:46 am   #9
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Default Re: ITT air compressor servicing

People often confuse 'pressure' with a compressor's ability to do useful work.

More important is 'capacity' - cfm - (cubic feet per minute), there is no point having a compressor at 1000psi if it only has a capacity of 1cfm.

The one in the picture appears to have a 100PSI rating but no capacity shown (that I can see) and from the small tank, I would suggest it is going to be borderline for anything other than the smallest of spray guns (although it would probably be more than adequate for an air-brush).
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Old 19th Aug 2020, 6:16 am   #10
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Default Re: ITT air compressor servicing

From my hazy memory of life in the late 70s, I think my colleague and I used to share one of these units. We used it to supply air to a precision calibrator for force balance units and other pressure driven instrumentation. I recall doing a big strip down and maintenance job that included fitting new rings. This was a delicate task as they were carbon - the whole shebang being 'oil-less' - and we locked the workshop door and held our breath as we fitted them. I think we performed this replacement because it would no longer reach its rated pressure (or the pressure that we required from it).
BC

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Old 19th Aug 2020, 4:59 pm   #11
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Default Re: ITT air compressor servicing

If you're worried about the explosion-risk of an old tank and aren't prepared to get it ultrasounded/certified, do what a lot of garages/tyre-places do and put the compressor in a little 'rabbit hutch' outside your workshop area.

(this will also save your ears from the racket of the motor and compressor).
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Old 19th Aug 2020, 5:03 pm   #12
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Default Re: ITT air compressor servicing

Ever seen a tank go up? The hutch better be made of reinforced concrete.
 
Old 20th Aug 2020, 12:38 pm   #13
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Default Re: ITT air compressor servicing

Thank you for the good suggestions - oil-less operation would make sense then. I'll continue the strip down. There is some oiliness on the piston head, though perhaps its a carbon emulsion. There is also a sleeve that fits around the majority of the piston, as well as the two rings in grooves.

I was hoping it would be suitable for an airbrush for refinishing (I've never tried one) and I have a couple of empty Calor gas tanks that I had considered linking up for extra capacity. From examples I've read online it seems quite straightforward if basic safety precautions are taken.

I'm less concerned about rust now that it seems the angled vent is able to eject the water. I'll leave the big plugs alone.

My brother said he'd turned it on and it made much less noise than his cylindrical Machine Mart-type compressor. That's only a small one but has been fine for running the plasma cutter for our needs.

If I were to need new rings, where would they come from?
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Old 22nd Aug 2020, 6:17 am   #14
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Default Re: ITT air compressor servicing

It sounds as if you have the head(s) off now.
I was going to suggest that the heads and cylinders were left alone if the pressure was OK for your use - it really was a delicate operation replacing the rings and getting the pistons back up the bores again!
My possibly hazy memory of the 'service' that we did is that the heads had the cylinder sleeves attached or cast integrally. Is that correct? I don't recall what the cylinders were lined with. Maybe 'Nikasilled'?
Obviously in the late 70s we must have got rings etc very easily, but I would think that they would be impossible now.
If asked I would say that the unit that I used was not gold but a mid blue - like a 'British test gear' blue but I could be wrong!
BC
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Old 22nd Aug 2020, 9:39 am   #15
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Default Re: ITT air compressor servicing

I remember replacing the carbon piston ring in a compressor about 50 years ago. They were supplied as a continuous ring (toroid) which you had to carefully break into two approximately equal segments.
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Old 22nd Aug 2020, 12:39 pm   #16
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Default Re: ITT air compressor servicing

I've been stymied by the connecting rods and how to get them off the shaft - I think this is a job for one of those pullers, a tool I have never had but now have an excuse for. I thought it was a good idea to lubricate the bearings so need to get the shaft out from the rear part of the casing where the windings are. The pistons are getting in the way!

The fan was very brittle and snapped when I tried to remove it. It had lost a blade anyway so I was going to replace it. It pressed onto a splined shaft with a compressing metal ring collet to hold the nylon(?) split ring pieces jammed on to the shaft. I would hope that with internal and external diameter measurements I can fit a new fan...

The pistons have two thin rings of indeterminate material backed by metal ones, and a sleeve that covers the body of the piston below. All of these appear to be reasonably flexible, and have stepped joints that imply they were constructed that way rather than being continuous rings that had been broken.
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Last edited by Uncle Bulgaria; 22nd Aug 2020 at 12:47 pm.
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Old 22nd Aug 2020, 1:15 pm   #17
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Default Re: ITT air compressor servicing

The "big ends" look like sealed bearings to me that have leaked, replacement is the only cure.
 
Old 22nd Aug 2020, 2:56 pm   #18
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Default Re: ITT air compressor servicing

Metal rings and no lubrication seems a bit odd. I'd have expected something like Rulon, with a carbon ring in pole position.

https://www.seals.saint-gobain.com/p...ymer-materials

Are the bores of the cylinder chrome plated by any chance?

A puller should fetch the first big end race off of its eccentric, then you'll have to pull the eccentric itself to get the second race off. But, if the bearings feel good, loss of a little lubricant may not necessarily be a problem and further dismantling is not always risk-free.

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Old 14th Oct 2021, 8:05 pm   #19
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Default Re: ITT air compressor servicing

re-opened at OP's request.

Cheers

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Old 14th Oct 2021, 8:45 pm   #20
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Default Re: ITT air compressor servicing

Thank you CobaltBlue!

This has become a great looming project that I've finally knuckled down to, after becoming rather too enthusiastic, and having to break off the bearings and eccentrics. I ended up having to make new eccentrics (with the help of my brother and his lathe) and a suitable key.

The new bearings pressed onto the eccentrics and into the pistons with far less trouble than I'd imagined. My girlfriend had some leftover gold spraypaint of a rather superior type, so I've done a quick blow over to lift the original gold which was looking rather tired.

Now it's like a probe on a commemorative Soviet stamp for some bizarre space milestone. Just how I like it.

One O-ring is missing behind one cylinder bore attachment, so the air leaks out instead of going into the tank, but the thing goes round and is pumping.

The rings are actually some kind of carbon impregnated material, perhaps similar to the Rulon of Radio Wrangler's post. The steel rings go behind them, presumably to keep pressure outwards to make sure the rings are in constant contact with the bore (which is not chrome plated).

The new bearings have made a lot of difference, and it's certainly quieter than my brother's Axminster compressor. I've got some O-rings on order, so I'll see if adding the missing one pressurises the tank.
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