This week, I did some more research on the compressor after noticing the folllowing specifications on the end of the pressure vessel.
In case you can’t read it properly, it reads as follows:
Jahr/No 71 13086
Betr./Prüf.Dr 10/16 atü
Baumust.-KZ ZU 49
Inhalt-ca. 25 l
This is of course not in English! Roughly translated from German, with some research and guesswork on the abbreviations, it appears to read:
M.A.N. (truck and bus company)
(Manufacturing) Plant in Munich
Year/No 71 13086
Operating/Test Pressure 10/16 atmospheres over-pressure
Construction type (model) ZU 49
Contents approx. 25 l
So the pressure vessel has 25 litres capacity and looks to have been made in Munich, Germany in 1971 for the air brake system of a truck or bus and later reused as part of a custom-made air compressor.
Armed with this information, I did some research into testing the actual flow rate of an air compressor and found the following formulae:
The formula for calculating the flow rate of a compressor at http://www.hosereels.biz/blog/post/3469129 is:
TANK GALLONS x 0.538 x PSIG divided by SECONDS = flow rate in CFM (or cu ft/min)
Google tells me 1 L = 0.264172 US liquid gallons
1 CFM = 28.32 L/min flow rate
The German-language pressure units converter found at https://www.einheiten-umrechnen.de/einheiten-rechner.php?typ=druck told me that the operating pressure of 10 atü is approx 156.4568 PSI and the test pressure is 16 atü or 241.7968 PSI.
So, 25 litres is 6.6043 gallons. From initial testing, it took approx 2:20 (140 seconds) to fill the tank from empty to a PSIG (gauge pressure) of approximately 95 psi when the cut-out switch kicked in, so the flow rate is about 2.4110 CFM or 68.2807 L/min.
This will help a lot with choosing air tools to use with the compressor, as most of them specify required flow rates at a specific pressure.
Further research told me that air compressors need their pressure vessels drained regularly, so I had a look for the drain valve. Unfortunately, I removed the whole valve assembly instead of just opening it, and got this oily,watery mess all over the pavers underneath the compressor as I quickly moved it to a more suitable work location.
The drain valve assembly had a lot of the acrylic paint used to paint the compressor on it, as well as some oily gunk coming out. I put it on a large rag to clean it up.
I went through my large spanners until I found the right size to unscrew the parts of the valve from each other. These turned out to be 19 and 27 mm.
Once freed from each other, I could see just how dirty the parts were.
I set about cleaning them up with some brushes and WD40.
It didn’t take long to clear the gunk out, so I kept cleaning.
Once most of the acrylic paint had come off, the brass seemed to be in pretty good condition!
I cleaned off the last of the old teflon sealing tape and applied a fresh layer.
The inside of the thread on the pressure vessel seemed to have a lot of gunk too, so I cleaned it off as well as I could.
With the mounting thread as clean as I could get it, I replaced the outer section of the drain assembly.
I put the drain plug back in and returned the compressor to its normal position before tightening the plug again.
I also noted the pressure cutoff switch had this assembly on the bottom.
There were quite a few cobwebs on the bottom!
I cleaned up the brass pieces as well as I could.
THen replaced them where I found them, only a little more tightly.
This looks to be an adjustment screww that has been painted over, so I’ll clean that up next time I work on the compressor.
Much better – no more cobwebs!
I haven’t properly tested the compressor again since draining it and cleaning these parts – I’ll see if there is any difference once I’ve cleaned the other adjustment screw.
I took several photos of the relief valve from different angles after noticing some writing engraved on it.
Using a combination of Google searching the partial wording I could make out, I was able to decipher that the following information is engraved on it:
SIZE 1/4 IN. FIG NO. 48.A
SIZE 3/8 SEAT
SET AT 50
KUNKLE VALVE CO
FT. WAYNE IND. US
If the release pressure of 50 PSI is correct, it seems I have either have a faulty pressure release valve or a faulty pressure gauge, as the release valve only starts releasing air at around 90-95 PSI on the gauge.
The next steps for the compressor will be checking and topping up the oil for the compressor motor, then replacing the pressure gauge and release valve