Air Compressor Question

[Tyler]

I finally got my air compressor running--I think I mentioned that I was in-process on a Craig's-List-treasure rebuild.

Anywho, I kick her on for the first time tonight, and sure enough she compresses. The thing is, I have no idea how to measure the success of my rebuild. Can someone tell me if these numbers compare OK with their compressor?

Here's the specs:

2-stage compressor
5-HP motor (truly a 5HP, not a max 5HP--the motor is HUGE)
80 gal tank

Time from 0-125 psi is exactly 5 minutes. According to my calculations that about 18.2 CFM. The compressor is supposed to do something like 17 CFM at 175psi. The pressure switch kicked off at 125 psi though.

Is 5 minutes about right for 0-125 psi?

I was really excited that the compressor was a 175 psi unit because that seemed like it would blast a lot without needing to kick on. I was surprised when the unit kicked off at 125 psi. What pressure do your units kick off? 125 psi? Higher?

Thanks for the help. Bottom line is I'm pretty sure I can start buying blasting stuffs knowing I WILL be able to use them. I'm just trying to see if I am in the ballpark for what to expect from a compressor like mine.

Tyler

[RadDavis]

Hi Tyler,

My compressor is rated at 175 psi (tank pressure), and it kicks off at around 175 psi. It's got a 11 hp peak, 7.5 hp running (whatever that means) motor.

It says 25 SCFM @100psi. on the compressor.

I don't know if this helps at all, but you should be able to blast with your setup. It might not get up to pressure and kick off while you're blasting though.

Rad

[KurtHuhn]

It sounds like your compressor is rated similarly to mine, with the exception that I've only got a 60 gallon tank. I've set it to kick off at 135 PSI to save my regulator and moisture trap, which are only rated to 150 PSI.

When I use a 15 CFM jet in my gun, the compressor runs pretty much constantly during blasting. Obviously, the gun with a 5 CFM jet isn't as hard on it. I just make sure to change the pump oil regularly, and I've never had a problem.

[Daniel Y]

The rule of thumb I was taught is that you do not want the compressor to run more than half the time. I don't know how long it takes to sand blast the average pipe. but lets say it takes 15 min but your compressor kicks on after 5. you can continue to blast for another 5 min then you need to give it a break for 5 and then start again. It is a real pain but that is how I have to do nearly all of my air tool type work because I don't have a really good compressor. I also pretty much ignore the rule unless the compressor is going to run for a half hour or so. I figure if a piece of equipment cannot run for a half hour solid let it break I need to replace it anyway. so for the first 30 min or so I let the air flow determine if I need to pause for a moment and let the compressor catch up. Other than annoying the less than half time with the motor running rule should keep you from harming your compressor regardless of how well it gets the job done. I find it very helpful to figure out just what tools I should use with my compressor and which ones I shouldn't. I paint houses with my little dual tank portable. a huge pain with lots of breaks but it gets the job done eventually and shows no signs of wear or tear.

[Tyler]

Ok, new data.

I adjusted the pressure switch up, and tested the "make up" time. High side is now 160psi, and low is 110psi. I think that my pressure gage is low though. This is a new gage--the old one had a cracked glass--but the old one measured 20 psi higher. At any rate, it made up in 2:06.

First question, what differential do you guys run? (It's adjustable on my switch.). 50 psi seems a lot.

Second, 2 minute make up on 110 (130?) to 160 (180?) psi sound decent?

EDIT: I just calculated that a 2:06 make up on 50 psi in a 80 gallon tank is 17.33 CFM. My manual on the compressor says that it'll do 17.4 CFM at 175 psi. If my gage is really 20 psi off, and I did go up to 180 psi, then it sound like I'm running pretty doggone good!

[RadDavis]

Ok, new data.

I adjusted the pressure switch up, and tested the "make up" time. High side is now 160psi, and low is 110psi. I think that my pressure gage is low though. This is a new gage--the old one had a cracked glass--but the old one measured 20 psi higher. At any rate, it made up in 2:06.

First question, what differential do you guys run? (It's adjustable on my switch.). 50 psi seems a lot.

Second, 2 minute make up on 110 (130?) to 160 (180?) psi sound decent?

EDIT: I just calculated that a 2:06 make up on 50 psi in a 80 gallon tank is 17.33 CFM. My manual on the compressor says that it'll do 17.4 CFM at 175 psi. If my gage is really 20 psi off, and I did go up to 180 psi, then it sound like I'm running pretty doggone good!

I don't think 50 psi is a lot. Mine cuts on at around 125-130 or so and goes back to 175.

The makeup time sounds decent, but the test will come when you're actually blasting. if the motor comes on, catches up and cuts off while you're blasting full bore, then you're good.

Rad

[Tyler]

Ok, new data.

I adjusted the pressure switch up, and tested the "make up" time. High side is now 160psi, and low is 110psi. I think that my pressure gage is low though. This is a new gage--the old one had a cracked glass--but the old one measured 20 psi higher. At any rate, it made up in 2:06.

First question, what differential do you guys run? (It's adjustable on my switch.). 50 psi seems a lot.

Second, 2 minute make up on 110 (130?) to 160 (180?) psi sound decent?

EDIT: I just calculated that a 2:06 make up on 50 psi in a 80 gallon tank is 17.33 CFM. My manual on the compressor says that it'll do 17.4 CFM at 175 psi. If my gage is really 20 psi off, and I did go up to 180 psi, then it sound like I'm running pretty doggone good!

I don't think 50 psi is a lot. Mine cuts on at around 125-130 or so and goes back to 175.

The makeup time sounds decent, but the test will come when you're actually blasting. if the motor comes on, catches up and cuts off while you're blasting full bore, then you're good.

Rad

Thanks Rad.

Just for grins, here's the beastly beauty:

[SimeonTurner]

Looks like something from a WWII submarine. LOL

[RadDavis]

Ok, new data.

I adjusted the pressure switch up, and tested the "make up" time. High side is now 160psi, and low is 110psi. I think that my pressure gage is low though. This is a new gage--the old one had a cracked glass--but the old one measured 20 psi higher. At any rate, it made up in 2:06.

First question, what differential do you guys run? (It's adjustable on my switch.). 50 psi seems a lot.

Second, 2 minute make up on 110 (130?) to 160 (180?) psi sound decent?

EDIT: I just calculated that a 2:06 make up on 50 psi in a 80 gallon tank is 17.33 CFM. My manual on the compressor says that it'll do 17.4 CFM at 175 psi. If my gage is really 20 psi off, and I did go up to 180 psi, then it sound like I'm running pretty doggone good!

I don't think 50 psi is a lot. Mine cuts on at around 125-130 or so and goes back to 175.

The makeup time sounds decent, but the test will come when you're actually blasting. if the motor comes on, catches up and cuts off while you're blasting full bore, then you're good.

Rad

Thanks Rad.

Just for grins, here's the beastly beauty:

Verrry pretty.

Rad