Compressor mods

[bonz_d]

Winter dole-drums has set in bringing to much time to think.
So here is the thing. I have and older craftsman compressor, it is a twin cylinder single stage belt drive pump, 1hp with a 12 gal tank. The pressure switch has I believe a 70 to 100lb set points. has a 9.5cfm displacement, 7.5cfm @ 40psi and 6.1cfm @ 90psi delivery.
So far it is doing what I need it to do and I have prayed with it. Small jobs it keeps up and supplies the gun I have pretty well. One of the things I'm looking at is the motor. It's getting old and drawing a lot of power to start and thinking of replacing it. Would there be any advantage to going up to a 1.5hp or a 2hp motor? Next what would I gain by adding a second or larger tank? How much tank could I add? Last question is with the pressure switch. Why the 100lb shut off set point? Most all of the replacement ones I see are 125psi shut off.

 

[MTboatguy]

You might see if you can find the original information that craftsman put out on that compressor, you would then be able asses how much you can play with it, for some reason they set the cut off point at 100 pounds, many of the consumer compressors I run into are set at 100lbs, all of my compressors are commercial models my current compressor is set to cut off at 135lb.

 

[mla2ofus]

Find the stamped tag on the tank to see what psi it's rated for. A larger HP motor won't hurt a thing .
Mike

 

[thumpar]

With the small units it might just be cheaper to buy a whole new one than to try to mod it.

 

[bonz_d]

I do have access to electric motors very cheap so that's a wash as far as looking for a different compressor and I can find non-running 20gal compressors all the time locally on CL for next to nothing to add or swap to a bigger tank.. Thing is that I have to keep this at 115v. no way to get 220/230v cheaply into the detached garage

 

[bonz_d]

OK wait. before this gets to far out I do have a lot of experience with industrial compressors. Part of my job is care and maintenance for 3 100hp IR screw compressors that are all piped together and run thru a sequencer. One off, one lead, one lag or all three depending on demand. In another part of the plant we have a 50 year old Champion 20hp 2 stage that keeps chugging away.

The one I have the pump is in great shape and is very quiet. I have looked all over the internet and there is no info available for manuals. The new stuff I see on the market today in the 2-5hp capacity are junk in my opinion. I just threw away a 3 year old Craftsman 1.5hp because it seized up. If I had the power available in the garage, which I don't, I would be putting in a 5hp 60gal 2 stage Champion compressor that I could buy from a friend for much less than a decent brand new one.

 

[MTboatguy]

How far is your power meter box from your garage? I thought it would be expensive to run 220 into my detached garage and was really surprised at how inexpensive it was, of course the wire was the most expensive part of it, but only took me a couple of hours with a rented ditch witch and some inexpensive underground conduit. Of course where I live, you have to hook your own power up to the house so putting power to the garage was no big deal.

 

[Scott Danforth]

I think your limited due to the single stage pump

single stage compressors do not like high pressure because there is a limit to the pressure you can build up in a single stage setup vs a 2-stage. there is also the heat buildup during the compression stage, going higher than 100psi in a single stage builds a lot more heat.

depending on the year, the craftsman pumps were made by a variety of companies, including Campbell Hausfeld, devilbiss, and Ingersol Rand

take the first 3 digitis of the part number - that is the manufacturer code. then look here http://vintagemachinery.org/Craftsman/manufacturers.aspx

 

[bonz_d]

Thanks Scott for the Link. It confirms my belief that the pump is a DeVilBiss, 919. Last night I was also able to find a link to another set of compressor pumps listed at hammerwall.com.

The one I have is a 158 series and the one I found was a 176 series. In that series there are 4 models listed, two 1hp, a 2hp and a 3hp. The two 1hp models have the same specs with what looks like different motors and both have a cut out pressure at 100psi. and a displacement of 9.2cfm. and uses a 12gal. tank. The 2hp has the same pump specs as the 1hp but with a 220v motor and a cut out pressure of 125psi and a displacement of 11.7cfm. and uses a 20gal tank. The 3hp shows a larger piston displacement so I assume it's not the same pump head.

So my question now is this, is the cutout pressure limited by the motor hp as the pump appears to handle the higher pressure with a larger motor. Next, how do these same pumps with the same static displacement increase output CFM by 2.5CFM by just going to a larger motor and higher PSI?

Lastly, no one has addressed the question of a larger tank. Advantages or Disadvantages. I have read that it effects the duty cycle and sort of understand the effects though not completely.

 

[mla2ofus]

With the same pump output and a larger tank it will take longer to pump back to cutout pressure. IMO really no gain. If you're using a high air consumption tool it will run longer but you'll be waiting longer for it to regain pressure.
Mike

 

[gm280]

A larger tank using the same motor/pump will take a lot longer to build pressure but can also take longer between cycling as well. The cut off pressure can be changed. In fact some are easily changed without buying a new one. I think my setup cuts out a 110psi. I use mine near daily and I do have 220 available (put it in myself) and eventually I plan on a stationary 60 gallon or even 80 gallon max size compressor. I do own lots of air tools and my dual action 6" IR orbital sander will work for only about 30 seconds to a minute seconds petering out. Then I have to wait for a build up again. That gets old real quick. The more tank capacity the longer it will take to build up pressure, but it will work longer before cycling again to rebuilt. Maybe if you can't run 220 lines, you could tandem setup a couple of smaller compressors to yield a larger capability. Just a thought.

By the way. how's the flu going? I hope a lot better now!

 

[bonz_d]

Thanks Mike. I assume this is why Craftsman sized the tank this way and call it a Paint Sprayer.. At 40psi I can spray a gun cup and it will cycle once w/o appearing to lose pressure at the gun and only runs about 1 minute to refill, so it recover pretty quickly. So maybe going to a larger tank isn't the way to go.

 

[bonz_d]

Thank gm! So the cycle time is what I believe to be called part of the duty cycle? Would like to get this set up so that it's cycle time is about what it takes to shoot a cup of paint. Therefore I'm thinking 90psi cut in and 125psi cut out as opposed to the 70-100 it has now with a tank sized to reach that demand and time frame.

I hear you on the usage. That old 20hp piston compressor at work will cycle pretty frequently when we are using air tools and I believe that's on a 200gal thank.

Thanks for the thought! The recovery is coming along very slowly from this flu. I am now able to eat small potions of solid food and hold it for awhile. Don't know if I'm ready for pizza or BBQ ribs yet.

 

[bigdee]

T

So my question now is this, is the cutout pressure limited by the motor hp as the pump appears to handle the higher pressure with a larger motor.
YES

Next, how do these same pumps with the same static displacement increase output CFM by 2.5CFM by just going to a larger motor and higher PSI?

With a larger motor you can increase speed by changing pulley size. More RPM= more cfm

Lastly, no one has addressed the question of a larger tank. Advantages or Disadvantages. I have read that it effects the duty cycle and sort of understand the effects though not completely.

Less (fewer) cycle times

^^^

 

[bonz_d]

Thanks bigdee. So increase RPM = increase in CFM? Fewer cycles = longer usage and longer recovery time? Hope I'm getting this right.

 

[mla2ofus]

You need to find the max RPM for your pump. You shouldn't overspeed an engine and a comp pump is the same as an engine. Too much overspeed and you'll have a hole in the block JB weld can't fix.
Mike

 

[thumpar]

Are you just using a nailer/stapler gun off it or bigger tools also?

 

[bonz_d]

You need to find the max RPM for your pump. Mike

I understand this but so far that is the one spec I haven't been able to locate. I suppose I could find what motor RPM the 2hp is running.
No high demand tools other than the spray gun.

 

[gm280]

bonz_d, please don't make the mistake of just covering your present needs. Because sure as shooting, you will make a decision to buy something that will tax your present setup leaving you wanting bigger. That is how it works with me anyway. As far as spray guns go, I use to spray with a 1hp Craftsman compressor for a really long time before buying a larger unit. But I now want to be able to run sanders and such and my present setup is lacking in that capability. So a newer stationary compressor is in the future for certain. And I can easily use a little portable tank for issues away from the shop... It is amazing how much faster a pneumatic 6" dual action IR sander takes off paint and rust compared to electric setups... Not even in the same class!

 

[bigdee]

I understand this but so far that is the one spec I haven't been able to locate. I suppose I could find what motor RPM the 2hp is running.
No high demand tools other than the spray gun.

Use a 4 pole (1725 rpm) motor and regulate speed with proper pulley size. DO not use a 2 pole (3600rpm) motor on a compressor it does not have enough torque.
No matter what you do though you are still limited with 120 volt. It takes about 1hp to = 4 cfm. 2hp on a 20 amp circuit is pushing it.