air compressor question

[fredf]

am thinking of upgrading my compressor, probably something similar the $400 home depot 4hp 60 gallon vertical. it lists cutout pressure at 135, does anyone have a clue what the cut in pressure (where it starts) is?? I am trying to figure how much it will cycle

fred

[PTSideshow]

It will depend on how much air you are using in the application.
If it has an ASME stamped tank it is made by the same company as the Campbell Hausfield ones they share the same parts service 800 number 1-800-543-6400 you can call them and see if the can tell you with out the model number.

[andy_b]

from what i have seen on most compressors in that style and range, the cut-in pressure is around 120psi. as Glenn stated though, how much it cycles will be more a function of how much air you are sucking out of it. if you're running a nail gun, it will turn on very infrequently, if you're using a needle scaler it will run constantly.

andy b.

[radkins]

Compare the compressor [email protected] PSI to the CFM of the tool(s) you plan to use, most them will be rated at 90 PSI except for spray guns.

One thing to watch out for when figuring based on CFM however is that they tend to stretch the numbers to the breaking point, fact is most of the time they lie about them. Point is a compressor can be expected to produce less [email protected] PSI then they claim and a tool will use more CFM than it claims so figure at least a 10% differential and you will be close.

[Bill Pace]

Perhaps you missed this recent thread on this similar subject, lots of good info in it ---

http://bbs.homeshopmachinist.net/showthread.php?t=37364

It may not have addressed you primary question about on/off pressures and it can probably only be answered here in a general way -- the info shud be on/in the units literature or - usually - on a decal somewhere on the unit itself. Roughly, its usually on at 90 and off at 120. but obviously that will vary...

Do do some good research on this subject - there is such a wide selection of these - almost necessity - shop tools that you wanna make a good choice when you commit to one. The unit you describe is probably one of the 'oilless' types that are availiable everywhere and while they are popular, and many in use -- they are horribly NOISY!! -- this is just one of many bits of info to consider in making your selection.

Another is - most air tools love air in large quanities! if you use a lot of this type tools, (sanders, grinders, etc) factor this in...

[Falcon67]

am thinking of upgrading my compressor, probably something similar the $400 home depot 4hp 60 gallon vertical. it lists cutout pressure at 135, does anyone have a clue what the cut in pressure (where it starts) is?? I am trying to figure how much it will cycle

fred

>The unit you describe is probably one of the 'oilless' types
Fortunately, it isn't, not even close. You can buy a nice compressor for $400.

I have one, cut in is about 85 PSI, out at about 125. In normal around the shop use it doesn't cycle much. This one is rated at 10 & 12 (90/40) and works much better with a die grinder porting heads and misc than the old 1.5HP unit. Route the air intake outside and it'll be fairly quiet. It's not much more noisy than my older Porter-Cable cast iron unit. This was $399 at Tractor Supply.

[radkins]

probably one of the 'oilless' types that are availiable everywhere and while they are popular, and many in use -- they are horribly NOISY!! -- ...

The oil-less types are usually only noisy for a while, after you use them a relativity short time they tend to get real quiet, VERY quiet in fact!

[Bill Pace]

tend to get real quiet, VERY quiet in fact!

Heh! and its pretty neat what a mess that short little rod/piston can do when it decides to rest after going round'n'round so fast, and quits making all that noise

[fredf]

The one I mentioned is NOT oilless -- for the reasons given. altho for one of my applications oil less would be an advantage. My wife has several fish tanks. and we coudl use 12 - 25 cfh at 1.5psig I am sick of replacing diaphrams in the aquarium pumps every few months. I have used a rotary vane compressor in the past and it worked realy well, but it too needed to be rebuilt every year or so. I use airtools quite a bit, and thought that SWMBO might approve a purchace for her tanks . . . .

It looks like the breathable air filters use a fine filter followed by a charcoal filter. I was figureing on one of those motorguard filters and some sort of charcoal filter on the feed to the fish

[Falcon67]

For fish, maybe one of the HVLP supply units might be better. You'll have to clean the air well - it'll have oil and moisture so a couple of filtering steps would be a good idea. An oilless would work - but bury it in the back yard about 8' down so you can sleep at night.

Now, I'll never buy another oilless again - but I did paint two cars with one. Yes it was a b$$$h and no I won't do that again.

[Willy]

does anyone have a clue what the cut in pressure (where it starts) is??

Maybe I've been blessed with always having had compressors that have an adjustable pressure switch, but don't all compressors have an adjustable switch?
If yours does it's a simple matter to set the cut in and cut out pressure where you like...within reason off course.
If yours is nonadjustable it would be a simple upgrade to incorporate one.
Below is a quick link to an example of what I mean.

Pressure switch

[fredf]

Willy

Most do adjust, but have a fixed differential. in the case of the one you linked to it is 30psi (off at 125, on at 95) you can raise or lower the max pressure, but the differential stays the same (100/70 130/100 etc)
I would guess that most have a differential in the 30# range, was just hoping to verify

fred

Maybe I've been blessed with always having had compressors that have an adjustable pressure switch, but don't all compressors have an adjustable switch?
If yours does it's a simple matter to set the cut in and cut out pressure where you like...within reason off course.
If yours is nonadjustable it would be a simple upgrade to incorporate one.
Below is a quick link to an example of what I mean.

Pressure switch

[Willy]

You're right Fred, the adjustment range is limited.
Even on pressure switches with an adjustable differential pressure adjustment that I've run into are usually limited to 30-40 psi, although I have seen several with a max of 50 psi of differential adjustment.

[radkins]

Your compressor so do as you like but increasing the cut-off pressure above factory settings is a mistake. In the first place it falls into the same category as a larger tank in that it increases stored volume but just as in the bigger tank this is a trade off that will gain nothing as far as running time, it will however give higher working pressure if that is needed for some reason but then even that comes at a cost. Trying to run a single stage compressor above it's designed cut-off will lead to increased heat (just a few PSI can increase the temperature a lot) plus overloading the motor since the set-up is not designed to pump that much volume at that pressure. Even if the motor and pump manage to handle the heat and excess torque you will certainly lose performance because as the pressure rises using a single stage pump efficiency falls off rapidly, the point is that by increasing beyond designed limits you will get an increased time-to-recover vs use cycle rate in addition to increased air temperatures. That is why you never see single stage compressors with high cut-out pressures from the factory. Increasing a two stage above 175 PSI will do the same thing but to a lesser extent unless the pressure is raised above 200 PSI where efficiency will start to fall off rapidly and motor overload starts to occur, in either case compressor performance falls off by going above the factory setting even by a small amount and trying to go a lot higher will result not only in lost performance but possible motor damage.

[PTSideshow]

The problem you will have with any compressor is duty cycle of the motor. You probably will not find a happy medium for the two major uses you have stated.
It would stay off a long time when used as an air pump for the fish. It will cycle like crazy for a needle scaler or other high volume air tool.
how to choose an air compressor
If you read the list of usage of air for assorted air tools down the page. You will get the straight facts on picking a compressor. The information applies to all compressors!