Curtis (a.k.a. “the pickle”) is the big green air compressor in the southwest corner of the metal area. It was purchased at auction in October 2011 and reconfigured to better suit our needs.
- Make: Curtis-Toledo
- Model: D97 2-stage compressor
- Tank: Horizontal ~100gal
- Motor: (HP, RPM, etc. tbd)
- Power: 3-phase (what voltage?)
- CFM: (???)
- Cut-in/out: (out at ~130psi, in at ???)
Operation is pretty simple for an end-user of compressed air. There is a control box on the right side of the tank with a switch and a knob. To power up the compressor, flip the switch to “timer” and crank the knob clockwise. This will enable power to the compressor for up to 30 minutes, after which it will automatically be disabled. Please don't use the other switch setting (which bypasses the timer completely) unless you need to and are sure you won't forget to turn it off when you are done.
Every air compressor draws moisture from the air, and it ends up in the tank. This is bad for a steel tank, so the water should be drained out. There is presently a manual drain valve on the right side of the tank with a hose connected. TO blow down the tank, put the end of the hose outside the shop door (warn anyone nearby!) and open the ball valve for a minute or so. This should ideally be done daily. You won't go blind if you do it too often.
We need some parts to rejuvenate the valve seals and diaphragms on top. This will hopefully take care of the air leaks. Parts and price lists: http://www.oemair.com/AirCompressorsandProducts/IngersollRandProducts/ReciprocatingPistonPartsandRebuildKits/CurtisReplacementParts/tabid/205/Default.aspx
cp-616-7 unloader diaphragm (need 2x)
vb-406 o-ring (need 2x)
http://us.fscurtis.com/support/discontinued.htm from “d97two_stagelot_no_d9745.pdf”: p/n VB407 “O” Ring, 7/16” ID x 5/8” x 3/32”
our best guess based on locating “7507” on this page: http://www.oringsusa.com/html/compounds.html:
NITRILE or BUNA-N or NBR; General Purpose, 70 Durometer
Later note: Karl thinks this listed O-ring is not the right size, based on finding and installing a smaller one that was perfect (detailed below).
Since the compressor has been operational, it has leaked air from the actuator mechanisms on the head. There are two actuators, and each one has a few potentials for leakage:
- There is an O-ring inside the vertical bore of each actuator that separates the inside and outside of the head casting. On the 1st stage, there is no notable pressure difference across this seal, but lacking this O-ring would theoretically allow a very small stream of unfiltered air to be sucked in through the gap, bypassing the intake filter. On the 2nd stage, this O-ring contains the pressurized air traveling from the 1st stage into the 2nd stage. Leakage past these O-rings would be detected next to the springs visible on the assembled actuators.
- Each actuator uses a fabric-reinforced rubber diaphragm to convert air pressure (or lack thereof) into linear motion. The diaphragms on both actuators are massively deteriorated and have very little rubber remaining on either side of the fabric. These diaphragms are sandwiched between two castings, and need to seal air-tight against the upper casting. (the lower casting is not a seal surface and merely backs up the upper casting and provides threaded holes for the eight machine screws that compress the sandwich) Note that these diaphragms are only pressurized (exposed to tank pressure) when the motor is off, and they are depressurized (ambient pressure) while the compressor runs. A leak that is present only while the compressor is off is almost certainly from this air source.
- The head cover plates that mount the actuators and allow access to the inside for maintenance have a gasket that seals against the head casting. Again, on the 1st stage, this seal has only a very small pressure differential, but the 2nd stage cover is holding in full tank pressure.
- The air lines for the actuators are small copper tubing connected with olive-style flare fittings. The shorter segment especially has been bent and dinged countless times over the decades. It is not presently leaking, but is fully capable.
9/2012 – Karl and Michael made diaphragms for both actuators from bicycle inner tube and installed them above the existing degraded rubber/cloth for mechanical support. The inner tube seals much better on the castings, but the uneven thickness of the rubber/cloth layers below prevents a perfect seal. Karl plans to make new diaphragms from much thicker Nice Ride inner tube that might not require fabric backup. Eventually obtaining proper replacements would be a great idea, but hey, we're makers. Right? It was also noted that there is an O-ring gland on a small part inside the actuator that is lacking an O-ring. It was full of black crusty gunk that maybe used to be an O-ring.
Karl's O-ring gland measurements: shaft OD: .365” (note that bore is larger!) gland's smallest OD: .255” approx gland width: .095” (typical slightly angled walls with filleted transitions)
10/2/12 – Karl procured and installed an o-ring of unknown specification, and it turned out to be a very good fit and seals the bore well. The official size is not known, but in case we need to track down more of the same in the future, here are my best attempts at measuring it: .375 OD, .250 ID, .070 thick. While the actuator was disassembled, I measured the bore (hastily) with a bore gage and mic. It's around .379”, which jives with my earlier observations using drill bit shanks that it was somewhere between .375” and .390”.
Diaphragm science perhaps useful later: http://www.simritna.com/news/brochures/Diaphragm_Engineering_and_Design_Manual.pdf
Options include copper, black steel pipe, and PEX. Karl knows several shops plumbed with PEX air lines that have had no problems. (PVC is a big no-no due to the shrapnel hazard if it bursts)
Drops at each logical place in the metal and wood shop would be killer. Then short coiled hoses can be used instead of dragging messes of tangled hose through the building. Karl strongly recommends Coilhose Pneumatics. They make a fantastic hose from a very soft material (not that stiff nylon crap) that hold up well and are nice to use. We have them at the bike shop. Pricey, but worth it.
A self-retracting hose reel on the ceiling in a few locations would be great as well. Maybe that thin blue hose will actually behave nicely on a reel?
Arduino-controlled solenoid, naturally.
Move the regulator/filter/etc to a wall mount with a rubber hose connection to the tank to isolate vibration.