Compressor recomendation

[CJK440]

your answering your own question here. so if the ir does everything you need then it seems you really just want to buy a new compressor just to have a new compressor. lol. nothing wrong with that. cant factor in sandblasting because you can never have a big enough compressor for that task.

Lol, guilty a charged. Yes I am wanting to buy a better compressor. I checked one of the 2 stage 80 gallon ones at Lowes this am. The pump has the CH logo right on the side. $999 and I can throw a 10% off coupon on it I think. Then less what I can get for my old IR unit. On paper it seems like a better unit from a performance standpoint.

Versus

 

[texasking]

Just be careful what rpm they are spinning the pump at. A lot of times they just take a small pump and spin it faster to make their numbers look better.This creates a lot more heat, therefore water, and kills the life of the pump. My Dad once had a pump off of a 75HP compressor that he modified to run off of a 10HP motor he had by changing pulleys. I believe it was turning 250 rpm and sounded like a Harley idling. Ran at very short intervals, lol.

 

[CJK440]

Specs say motor rpm is 3450 but I don't know they pulley ratio. By eyeballing the pulley sizes in the product photo it has to be considerably less at the pump.

 

[jcclark]

That 15 amp rating @ 240v for a total of 30 amps
means that motor is not 5 hp, more like a 3 hp.
And that pump speed is very fast, which means quicker wear
and more heat, more water.
You get what you pay for with a compressor.

 

[CJK440]

That 15 amp rating @ 240v for a total of 30 amps
means that motor is not 5 hp, more like a 3 hp.
And that pump speed is very fast, which means quicker wear
and more heat, more water.
You get what you pay for with a compressor.

That IR label is my current compressor.

The one I am looking at has an advertised 5HP motor with a 22 amp draw. The Pump RPM for that one is 1200.

 

[jcclark]

That IR label is my current compressor.

The one I am looking at has an advertised 5HP motor with a 22 amp draw. The Pump RPM for that one is 1200.

That sounds a lot better, that one should do all that you'll need.
This is a good example of how different 5hp compressors can be.

 

[CJK440]

The pump RPM number came from Campbell Hausfeld tech support. They confirmed the Kobalt unit I am looking at is just a rebranded CE5003 compressor.

I think I am going to give it a shot. I'm not fooling myself that this is an industrial grade unit, but for light use in a home shop I think I would benefit from the better performance compared to what I have.

 

[jcclark]

You won't regret it!
I'm on my 4th compressor, wish I'd bought this one first.
Would have been cheaper in the long run.
I have never bought a tool and later think I should
have bought a lesser one.

 

[Brad J.]

Usually a lot of good buys are on craigslist. Get a good saylor beall, quincy, kellogg for half the price and never look back. I wouldn't take a 1200 rpm compressor if someone gave it to me. Noise and water are the by products of box store compressors.

 

[CJK440]

Usually a lot of good buys are on craigslist. Get a good saylor beall, quincy, kellogg for half the price and never look back. I wouldn't take a 1200 rpm compressor if someone gave it to me. Noise and water are the by products of box store compressors.

I can relate to more noise at the higher RPM, but isn't the amount of water condensing out just a function of the ambient air humidity and to what it is being pressurized to?

 

[jcclark]

I can relate to more noise at the higher RPM, but isn't the amount of water condensing out just a function of the ambient air humidity and to what it is being pressurized to?

No, it's a matter of heat.
The more the compressor heats up the air the more water it will condense out.

 

[dhutton01]

I can relate to more noise at the higher RPM, but isn't the amount of water condensing out just a function of the ambient air humidity and to what it is being pressurized to?

I have puzzled over this too. I concluded that the compressed air in the tank is hotter and can hold more moisture which condenses when the hot air leaves the tank and cools down in the lines etc. In the case of slower compressors which generate less heat the moisture condenses out and falls to the bottom of the tank.

Don

 

[jcclark]

If you keep it cool enough, it doesn't condense out at all.
Remember, heated air expands a lot, more volume, so it can carry a lot more moisture.
Cool it down and it shrinks back,less volume, so the moisture has to go.

 

[dhutton01]

For a given amount of compressed air the moisture content is fixed and the same regardless of the compressor. It’s just a question of where it condenses out. In the tank or down the lines. A compressor can’t create moisture, the moisture is in the intake air regardless of pump speed etc.

At least this is my conclusion.

Don

 

[shine]

my compressor lives outside . my drier shows almost no moisture in it . but my tank will have a qrt or so in it each morning when i drain it . especially in the cooler months . i am rebuilding my old champion 5hp pump . i prefer it's slow speed and it builds up much faster . i bought it rebuilt in 82 . box store compressors are junk imo . most are 3hp rated at 5 . especially the ones that have SPL for the hp rating .
if you can hold an electric motor with one hand it damn sure is not a 5hp motor . they are massive .

 

[jcclark]

For a given amount of compressed air the moisture content is fixed
Don

True but the given amount of air changes. The amount of moisture doesn't so take
1 cubic ft of air with, say 5 drops of moisture, heated up becomes 2 cubic ft of air with the
same 5 drops of moisture. Now it's only 2.5 drops of moisture per cu.ft.
You just halved the humidity level.
That's why its called "relative" humidity.
This is why your house is drier in the winter months,
You bring in air and heat it up, it expands and makes the humidity much lower.

 

[John McGraw]

A true 5hp compressor will usually put out around 15 to 17 CFM @ 90psi.
Compare the amps the motor can draw, it's on the motor plate, that's the true
indication of the motor size. It's the only way to compare motors these days.
You can figure almost 10 amps a HP.
Compressor makers are known for putting little motors on big tanks, watch for that too.
I have a 5hp Eaton that pulls 23 amp a leg for a total of 46 amps.
It puts out 17 cfm @ 90 psi with a 1750 rpm motor. (a slower 1750 motor is better too)
It out performs a lot of 7.5 hp units like the ones Home Depot sells.
So compare everything carefully, and you'll see why some are cheaper.

The compressor he is talking about is a single stage compressor. A single stage compressor drops off CFM dramatically as the pressure increases, while a 2 stage compressor does not. IMHO, Single stage compressors are not a a good compressor to spend money on. They are cheap, but their performance is way short of a two stage compressor. For a fixed amount of horsepower, you can get large volume or high pressure, but you can't get both. Buy a good quality cast-iron pump that is two stage and has parts availability, and you will never regret it. I went through a string of cheap compressors in my younger days, but when they went south, as they always did, they were either not worth rebuilding, or parts were not available. I bought a Curtiss compressor years ago, and it just chugs along all day long without a single issue. Parts are cheap and readily available, as they have been making this same E57 compressor for over 60 years! When something works this well, you don't mess with it! By the way, it is way quieter than most cheap import compressors because it turns at a much slower speed. A lot of the cheap compressors use the same head for several different horsepower units, they just spin the pump faster, and wear it out faster as well.

 

[John McGraw]

True but the given amount of air changes. The amount of moisture doesn't so take
1 cubic ft of air with, say 5 drops of moisture, heated up becomes 2 cubic ft of air with the
same 5 drops of moisture. Now it's only 2.5 drops of moisture per cu.ft.
You just halved the humidity level.
That's why its called "relative" humidity.
This is why your house is drier in the winter months,
You bring in air and heat it up, it expands and makes the humidity much lower.

Absolutely! I have had guys try and tell me that their compressor does not make as much condensate as other brands, as I just smile and keep my mouth shut. All compressors will make the same amount of water for the same amount of air. The guys that tell me this are usually working with a fairly small tank and fairly close to the point of use. The air is just too warm for the moisture to condense out yet, but it will when it goes through the nozzle of a spray gun!
My compressor has a large tank, so the air can cool of well, the compressor only runs about 30% of the time, it is in a different building from the point of use, and the air line runs underground to the shop, which further cools off the air. After it enters the shop, it goes through a refrigerated dryer which drops the dew point to about 38 degrees, and then goes through a desiccant canister which drops the dew point to around -40 degrees. I only use the desiccant output for painting, and all other uses just use the air that is dried by the refrigerated dryer. This saves having to regenerate the desiccant as often. I have had enough moisture issues in paint over the years, that I now have a system that is dry as a popcorn fart! During the summer months, the drain on both the tank and the refrigerated dryer are discharging real frequently.

 

[dhutton01]

True but the given amount of air changes. The amount of moisture doesn't so take
1 cubic ft of air with, say 5 drops of moisture, heated up becomes 2 cubic ft of air with the
same 5 drops of moisture. Now it's only 2.5 drops of moisture per cu.ft.
You just halved the humidity level.
That's why its called "relative" humidity.
This is why your house is drier in the winter months,
You bring in air and heat it up, it expands and makes the humidity much lower.

I was referring to the amount of air that is consumed and compressed by the compressor, not the resulting compressed air. I think we have very different ways of viewing and explaining this but may in fact be saying the same thing.

Cheers,
Don

 

[John McGraw]

For a given amount of compressed air the moisture content is fixed and the same regardless of the compressor. It’s just a question of where it condenses out. In the tank or down the lines. A compressor can’t create moisture, the moisture is in the intake air regardless of pump speed etc.

At least this is my conclusion.

Don

Don, your post was absolutely correct. It helps if you look at moisture as grains of moisture rather than relative humidity. Relative humidity for a given volume changes based on temp, but grains of moisture does not. Relative humidity is just that, the amount of moisture in the air compared to what it is capable of holding. Warm air can hold more moisture than cold air, but this does not mean that the actual amount of moisture changes as the temp goes up or down, only the relative humidity. As you compress air, the volume of air increases, and the grains of moisture goes up in direct relation to the volume of air. If you had 10 grains of moisture in outside air and you compressed that same air to 150 lbs, you would have 100 grains of moisture.

Since there is a known amount of moisture that air at any temperature will hold, the moisture that is in excess of what that air will hold, condenses out in the tank, period. Condensation only occurs until the air drops to 99.9% relative humidity, and never decreases any further, unless the temp of the tank drops lower. The fact that air in our compressed air systems is always at a saturated condition (100%), leads to the problems we have with painting. When this saturated air reaches the nozzle of your gun, the temperature drops dramatically, and moisture will condense out this cold stream of air. Everything that can be done to remove this moisture prior to it arriving at the nozzle of your paint gun, will be of great benefit to avoiding moisture problems in the paint. Cooling the tank off by placing it outside like Shine does, helps. The truth is that unless you drop the temperature of the air below about 34 degrees, there is a good chance that you could be condensing some moisture out at the nozzle of your paint gun.
How many times have you been running a grinder for an extended period of time, only to have the grinder get so cold that you had to put gloves on?
That is how cold the air can get when the pressure of compressed air drops substantially. In my opinion I can not imagine operating a spray booth with out at least a refrigerated dryer at the minimum, and with a desiccant dryer if you really want to be safe.