I NEED A Compressor

[f350ca]

Both the motors look suspiciously small to be 5hp but the current is about correct. The triple cylinder looks very china. Arvid is right not much after cooler there.

[Sunset Machine]

Doubt you'll be disappointed, Ed. It's just an air pump, simple as can be. Go for a belt-driven cast iron block.

Pretty sure "Assembled in USA" is just a way of reducing import duties. They probably have it figured right on the cusp of profitability, rather than some patriotic or quality thing.

[EdK]

(05-07-2014, 07:43 PM)f350ca Wrote: Both the motors look suspiciously small to be 5hp but the current is about correct. The triple cylinder looks very china. Arvid is right not much after cooler there.

The triple cylinder pump is made in Italy, not China. I don't know what an after cooler looks like so is that something I should be concerned about?

Ed

[EdK]

Ok, if you had about $1000, +/- a couple $100, to spend, what compressor would you buy?

Ed

[arvidj]

(05-07-2014, 08:16 PM)EdK Wrote: I don't know what an after cooler looks like so is that something I should be concerned about?

Ed

Hope you don't mind yet another comment from me.

Two of the things that happen when you compress air is that (a) the compressed air and everything associated with compressing it gets hot and (b) any water vapor that is in the air does not go away.

The heat from (a) is a problem because high heat is not a good thing in general for motors, pumps, gears, etc. and heat also makes addressing (b) difficult.

To address (a) the compressor pump is usually finned, has a cooler on the output and the large pulley that drives it usually has the spokes in the shape of a fan blade to move air over the pump and coolers. There may also be an after cooler on the output in an attempt to reduce the air temperature before it goes into the tank.

I will use my 2 stage compressor as an example. Between the output of the first stage and the input of the second stage there is a cooler. And obvious attempt to get rid of some of the heat generated by compressing the air in the first stage and to give the second stage cooler, denser air to work with.

   

On the output of the second stage there is another cooler that attempts to get rid of some of the heat generated by compressing the air in the second, final stage before it goes into the tank. This is what I would expect to see on any reasonable pump and in my mind neither cooler is an aftercooler.

   

In my case when I ordered the compressor I had them add an aftercooler. It goes after the second stage cooler and before the tank. Note that it is directly over the drive pulley and is therefore in the cooling air flow that the pulley generates.

   

You may ask "How hot can this get? After all its just air." I can suggest that the input to my aftercooler ... that would be the temperature of the input fitting to the aftercooler and reflects the temperature AFTER the first and second stage coolers has done their jobs and the temperature of the air that would normally be going into the tank ... is over 260 degrees Fahrenheit according to my heat measurement gun. The temperature of the aftercooler output fitting is somewhere in the neighborhood of 80 - 90 degrees Fahrenheit. The ambient temperature of the basement is usually 70 or less degrees Fahrenheit.

(b), water vapor, is the other problem as paint guns, plasma cutters, blasting cabinets and other things that might consume the compressed air do not like moisture. When you take 14.7 psi air and compress it to 175 psi you are taking roughly 10 cubic feet of air and making 1 occupy 1 cubic foot. You have also taken all of the water vapor that was in that 10 cubic feed and putting it in the same space. In other words your 80 gallon air tank now has a heck of a lot of water vapor in it along with all that air.

Which brings us back to the hot air issue ... yes, at this point you are thinking I am full of it. The cooler air is the less water vapor it is willing to support. Cooling the air will cause it to 'rain'. If you cool the air down a lot before it goes into the tank then hopefully it rains in the tank. If you don't cool it down before it goes into the tank then it may rain in the tank if you are lucky ... after all it is a big tank and is cool to start with ... or it may just pass thru the tank and move on to the lines and what ever is down stream.

Is it really that big a problem for the home air system? If you don't use the compressor very often the vapor laden air has plenty of time to dwell in the tank, cool and rain. If you are doing things that are ambivalent to water vapor, I think lots of air tools with proper lubrication may fall into this category, again no problem. If you have some other means of getting the moisture out before it is consumed ... like a desiccant dryer ... then it might not be an issue.

However if you are doing anything that does not like water vapor it is a PITA to get rid of. I will suggest that you don't have to go thru much in the way plasma cutter consumables or gum up you blasting cabinet or mess up a paint job to decide that you need to pay the price to resolve the water vapor issue.

So an aftercooler or a refrigerated air dryer is not a "Must Have" but more along the lines of "If you do this or that then it is a very nice to have" item.

Just to give you an idea of what else you might want to consider ... note again not "Must Haves" ... you may want an air filter and a regulator that goes between the tank and the air distribution system. This would be in addition to any "point of local use" stuff you might employ. What I have looks like this ...

   

The 175 psi air from the tank comes in on the left side, goes thru a 5 micron filter, then a .01 micron oil and water separator and filter, then to a desiccant dryer, thru a regulator that is set at about 130 psi and finally back up to the 1 inch copper distribution system to the garage and the other part of the basement. Note that "oil injectors" are a "point of local use" only and I have a couple of hoses that are specifically for that purpose. I did not spend all that time and energy getting a clean air system to then pollute the entire system with oil.

I am not suggesting you need any of this to have an effective system. All I am presenting here is one example of what can be done and why I did it. Please feel free to pick thru this mess and decide what might be of value to you.

Arvid

[EdK]

Wow! That's a very informative post Arvid. Thanks for taking the time to share your knowledge. You obviously did your homework before you bought your compressor. You have a really nice setup.

Ed

[Sunset Machine]

It's been awhile, but I've bought, installed and serviced a number (more than ten fingers will let me count) of commercial sized (7-1/2 to 10 HP) compressors and don't recall any of them coming with an aftercooler, I usually added a dryer to them. I think it would be a mistake for a manufacturer to equip a compressor with an aftercooler (they come as water, air, chemical, or freon cooled and are downstream from the tank). They are accessories.

To the best of my knowledge, all two stage pumps come with intercoolers between the cylinders (copper tube w/fins located in the flywheel airstream). This is so the second stage doesn't burn up (valves getting carboned) and no other reason. I don't think it's possible to control water except downstream from the tank, not in the environment I'm familiar with. The method I use at home (very intermittent use) is to leave the tank drain cracked open all the time and to turn the motor off when not using it. Commercially, a solenoid and timers ("electronic tank-drain") are used to pop off every day. They're a huge improvement over the float and differential pressure types.

As to what brand, I've seen a number of Speedaire's used in dry pipe fire sprinkler systems with descant dryers. You kinda want something light-duty, reliable and cheap there... Like at home, although mine is a Cambell-Hausfeld because is was grey and matched the lathe.

[Highpower]

(05-08-2014, 08:30 AM)Sunset Machine Wrote: Commercially, a solenoid and timers ("electronic tank-drain") are used to pop off every day. They're a huge improvement over the float and differential pressure types.

Yup. As long as they are working. The last shop I worked in had a sizable rotary screw compressor like this one. Extremely loud and runs non-stop.
   

It had an electronic drain that was set to pop off every two hours. Problem was the owners were too cheap to keep up on the maintenance of the system. Occasionally the drain would stop operating and we would all start getting a water mist through our air tools. We would complain about it to the management, but of course nothing was ever done about it.

One day the compressor started sounding real funny. The temp gauges were almost pegged. When attaching a blow gun to an air hose to blow off some parts, you would have thought you had grabbed the high-pressure washer by mistake. Not kidding. It would shoot a spray of water out as good as any self-serve car wash.

The compressor finally gave up and quit running. With no air in the shop they HAD to call in a service crew to get it fixed. Besides having to repair the compressor, drain valve system, and the refrigerated drier, they ended up draining 55 gallons of water out of the tank manually. (120 gallon tank.)

[f350ca]

My Devilibis has after coolers after the second stage cylinders, they're cast iron because of the pressure, the intercoolers between the cylinders are aluminum. Without the after cooler your putting hot air into the tank which is going to shrink and drop the pressure. Wouldn't be to remove moisture, its there until you extract it.

[Sunset Machine]

I'll be darned. A factory aftercooler. Looks like there's one on that Sullivan too, but for what those cost I'd kinda expect one. As to tank drains, I'm not real sure opening every two hours is a good idea. I have a tip: install a small wye strainer horizontally ahead of the auto-drain with the wye up. This is upside down. The drains plug with rust, the strainer will keep the chunks out. Upside down, the chunks will rattle and roll, turning into silt that will pass through the drain. Just remember: you read it on the internet.

Field trip. I went into an "industrial supply" and spotted a DeWalt vertical compressor, and now I see what Ed is up against. The pump looked bad, like they don't know how to make castings. It cast a dark cloud over the whole compressor. I was afraid it was going to fall over on me so I left.