Air Compressor FAQ’s – Part Three
Part 3 of a three part series.
DOES IT HAVE A CERTIFIED TANK THAT MEETS ASME STANDARDS?
All of our BendPak TRI-MAX™ extreme duty compressors from BendPak feature 80-gallon tanks manufactured by Manchester Tank, the world’s premier manufacturer of pressure vessels, founded in 1946. No matter what Air Compressor you get, make sure it has an ASME compliant tank.
SHOULD I GET ONE STAGE OR TWO STAGE?
Single stage compressors have one or more cylinders, and each cylinder pumps the air directly into the tank. Two stage compressors have a minimum of 2 cylinders, with the air pumping from one cylinder
into the other and then into the air tank. Typically, a two cylinder two stage compressor has a larger first stage which then pumps air through a cooling tube and into the smaller second stage cylinder at about 90 PSI, and then into the tank at 175 PSI. The reason for purchasing a two stage air compressor is if you need higher pressure. Most commercial auto shops will require a two stage compressor.
WHAT ABOUT DIRECT DRIVE OR BELT DRIVE?
A belt driven compressor’s advantage is that the pump can spin a lot slower than the motor, which means it will be more efficient with a lot less wear and tear. Direct-drive air compressor’s pumps turn at a faster RPM because the pump is directly connected to the motor shaft
and turns the same speed as the motor. Most electrical motors spin at either 2850 or 3450 RPM. Our BendPak TRI-MAX™ air compressors use a belt drive allowing the pump to run at a lower RPM than the motor. An air compressor RPM rating is the rating for the pump not the motor. But pump RPM and CFM is also relative to pump size and output. You can have two 7.5 HP air compressors running at the same 900 RPM but one may put out a higher CFM than the other because of piston
size. A large piston moving at the same RPM as a smaller one will put out a higher CFM. Inferior, cheaper air compressors usually have a higher RPM rating because their pumps are frequently significantly smaller than a comparable industrial model. Remember, higher RPM builds up more heat than a slower RPM.
OIL OR OIL-LESS?
Typical industrial grade air compressors are splash lubricated. Which means they have “flaps” on the connecting rods to splash oil up in the crankcase. As long as there is an adequate amount of oil in the crankcase, splash lubricated pumps will last a long time. Many of those cheaper direct-drive compressors you see out there are oil-less. This means they don’t use oil to lubricate the piston inside the cylinder. Think about it. Imagine your car engine running without oil.
Oil-less compressors typically use cheap aluminum cylinders, heads and pistons to help dissipate the heat. Aluminum does help dissipate the heat, but it warps and wears out much faster than cast iron.
Oil lubricated compressors are also much quieter. Oil-less air compressors are much more noisy because they don’t have oil in the pump to “muffle” the sounds.