I was able to purchase a gallon on Bauer synthetic compressor oil on EBay for $40. If you look at auto parts stores you can buy Royal Purple 100 synthetic compressor oil. Look at Filtertechs.com for Seco Lube 500. All of these are oils that won’t turn black before the recommended 50 hour oil change intervals recommended for a Carette. These should be perfect for an AV as well.
They should match up in theory. The accuracy and calibration error in analog pressure gauges is fairly substantial. I would trust the small gauge on the bottom of your Alpha filter the least of all. I'd go by the large gauge on the Carette and the one on your tank unless it is a small micro gauge. If it's a large gauge like ones on a Great White, Airhog, or Omega tank it should be fairly close to the Carette gauge reading. It would be a lucky oincidence if all three gauges read identical pressure after the PMV pressure has been exceeded. I wouldn't be too concerned unless one of yours is more than a couple of hundred PSI off the others. I saw a recently posted Youtube video from Edguns where he tested $50 Wika gauges 10 at a time. They were very inconsistent in their readings. It makes you wonder about the quality control testing that is done before analog gauges leave the factory.
Your Carette appears to be the base model. I don't see the auto moisture dump or the PMV that comes on the higher priced model that Joe sells. The side of the switch box which is directly behind the pressure shutoff gauge in your photo is where the hourmeter is on the deluxe version of the Carette. The red arrow in the photo points to the hour meter. It also has a Pressure Maintaining Valve and Automatic Moisture Drain which are both labeled.
Both tank input hose (output from compressor) and tank output hose (input to radiator) enter the tank from holes drilled in the top. Both hose ends are submerged and are at the bottom of the tank. We had two reasons for submerging the tank input hose: 1) to prevent air from entering the hose when the unit is turned off which would allow some of the fluid to drain; 2) to reduce air bubbles getting mixed in with the fluid inside the tank due to agitation at the surface as fluid is pumped into the tank. Since the radiator pump sucks the fluid out of the tank and doesn't rely on gravity, we could insert the hoses at the top of the tank, making it much simpler. We won't have any leaks at the bottom and we didn't need any fittings.
Good to hear that they are sending you a replacement gauge. I hadn't seen the Alpha filter when I previously looked at your photos. It is puzzling that you were sent a top of the line Alpha filter but not the full feature Carette. You don't need the factory PMV since the Alpha filter has one, but the auto drain and hour meter are useful features that you should have gotten with your order unless you opted for the base model.
I'd recommend getting a vibration activated hour meter that you can attach to the outside of your switch box if this is a feature you'd like to add. They are inexpensive. Check out Ebay and Amazon or Google it.
I like that one better! I was able to cancel my order before it shipped, so I ordered this one. The other one didn't say you could reset the hours. The description on this one says:
