air comp. ?

[rod]

I want to build an air comp. just for sand blasting [I do a lot of it]. I have a 40 gal. tank and a 3 hp 240 V motor. a friend gave me a 2 stage pump. I am almost sure it needs rings and reed valves. it has no ID on it, so must be a China. looks to be a 3" 1st and a 2" 2nd with maybe a 2 1/4/1/2 stroke. fairly sizable, & a 14" flywheel. probably cost $100 for parts and a lot of time.
I can get a brand new Harbor Ft pump, 2 cyl, 145 PSI [uses a 3 hp motor] for $112 + tax, and ready to put on.
my question is, what is the benefit of a 2 stage over a 2 cyl. single stage?
Thanks Rod in AZ

[Lew Silverman]

Do you know how many CFM the sand-blaster requires to operate properly? That will give you the best idea when building an air compressor. You usually want a unit that is at least capable of providing 1.5 times the air volume your tool requires and a large enough tank to keep the pump from having to exceed its duty-cycle rating. The two-stage units most often have a higher pressure rating than the single-stage units do, but for tools that use a lot of air (like a sand-blaster) the SCFM ratings are much more important.

I see the pump you are talking about in the new Harbor Freight catalog that arrived this morning, but it doesn't list a SCFM rating. You'll need it to make a decision.

Good Luck!

[1matcoman]

Originally Posted by rod

my question is, what is the benefit of a 2 stage over a 2 cyl. single stage?

Rod, the 2 stage unit will be almost twice as efficient as a 2 cylinder single stage. Meaning that it will fill your needs in approximately 1/2 the time that the smaller unit will. The dual-stage forces air in to the tank on both the intake AND the exhaust stroke, whereas the single stage will only do so on the compression stroke. Keep in mind that a sand blaster uses ALOT of air volume, so don't cut any corners with your air compressor build (or purchase) if you are planning on using it for that.