Two compressor questions ...

After reading many of the posts on this forum regarding compressors, I feel ready to pull the trigger and get a used compressor for my shop.

I am restoring a 1952 Pontiac. Most of the compressor use that I will have, is for a bead blasting cabinet and a DA sander. The rest of the air tools use relatively few CFM's.

I will be able to get by with an industrial 5HP. It will meet my needs with my hobby, with the cabinet needing 15 to 20 CFM, being the hungriest tool.

This being said ... I have been looking for a unit for about three weeks now. I don't want to get a new unit with a Chinese pump. Locally (New-Brunswick, Canada), the new makes are DevAir, Champion and Omega, with Quincy being 120 miles away. All of the new units are around the $2000 mark. I believe that all the pumps on these units are Chinese.

My budget was originally around $1200 for a used compressor.

The best option that I have found so far is this:

The pump is a Kellogg 452TV from the 80's I think, which has a rating of 7.5 (590 RPM) to 10 HP (846 RPM), that has been rebuilt. It sits on a horizontal 80 gallon tank which replaced to original one that was bad. It has a three phase motor and starter. The local compressor shop will exchange the motor and starter with a single phase 7.5HP Leeson, and sell me the unit for $1500 plus taxes.

My questions are:

Can this pump be run with a 5HP motor at around 400 RPM? From the information that I have gathered, It would seem that the pump has ring lubrication. Will running the pump at 400 RPM cause oiling problems? The main reason that I am exploring this option is because the unit will be inside my 16 x 24 foot shop, and I want to make it as quiet as reasonably possible.

If this is a workable scenario, then the 5HP motor will bring this unit down to $1250 plus taxes, which is right on budget for me, while giving me the CFM count that I need.

A second option would be to get the 7.5 Leeson at $1500 and put the compressor outside in a lean-to. It gets very cold around my neck of the woods, but this option would make the inside of my shop very quiet.

I am retired and the project is a hobby for me. I don't really have to make the compressor start on the coldest days ... I could take a break ...

I have read the comments on outside compressors and I am on the fence about this option ...

your thoughts are greatly appreciated ... thank you.

with the cabinet needing 15 to 20 CFM, being the hungriest tool.

Click to expand...

Not happening with 5HP or 400 revs

Leeson motors are pretty terrible. A 5HP Baldor compressor motor is like $325.

I like the old Quincy's. Have run 310's through 390's in my shop.

If you run a big displacement recip on the very slow end of it's rated speed and pressure (400 RPM/150 PSI) you need to be aware it may never come up to temp to burn the water out of the sump oil and keep the valves from crudding up.

I run a Quincy 350 Currently with a 7.5 HP single phase GE motor at 600 RPM. Takes about 45 minutes of continuous run for the compressor to get up to temp.

The Devair,and Champion, Saylor Beall pumps are made in North America, Do not know about Omaga.

I sell Champion and would look at the VP units, both the 5 and 7.5 hp units run at less than 900 RPM's and are quite, You can stand next to them and talk.

Ir, Chicago Pnematic, units are made over sea's to the west.
Most of the smaller compressor Co. are not making there own pumps but getting them from over sea's.

I would get a new unit and never have to worry about it, With a used unit you do not know the maintance record, or what type of shop it was used in, Body shops can use up a compressor in a couple of years,

Andrew
the compressor guy

Andrew

I would lean to the 7.5hp you will never be frustrated with haveing extra air. A 5 hp will run the hole time your blasting. As to starting in the cold iv never have had a proplem just keep good oil in it. And for the kellog I think 1500 is a bit high for a used unit is the motor brand new? That being siad a new compressor of that qulity will probly run you $5000 +.

We made compressors with found and second hand parts, then built one with a 4 cyl single stage pump, with 5 HP lots of air but only about 115 PSI or so.

Got fed up and bought brand new Champion 7.5 HP 2 stage upright, wondered what took so long as we blew money on other items and thought the other way was fine.

Buy NEW and don't look back.

I suggest the upright tank as it takes less room, can mount outside if you wish, make a house for it to keep it out of sight.

Good point about the 400 RPM being not viable ... and not getting the pump up to temp ...

I know the Quincy's are great ... at least the ones with the pressure oiling, but they are very rare in these parts so getting a used one is nearly impossible. I do not live in a densely populated area. My local area (100 miles around), only has about 125,000 people, so it's not like there are dozens of used compressors on the market to chose from every day.

I am not getting into an argument about whose new pumps are being made where ... I am NOT buying new so there is no point in me doing any research about them.

I guess I will be getting the 7.5 HP Leeson (NEW), and have the pump spin at 600 RPM. Two separate dealers have recommended against the Baldor motors. One of these dealers still sells them!

Thank you guys for your input. It has been helpful.

Now I need to figure out the best way to pipe the airlines ... and make it as quiet as possible. I already plan to pipe the intake to the outside air.

Most reciprocating compressors are good down to about 450 RPM, and not much over 900. I would go as big as you can afford-and then go bigger. I have a t-30 IR unit, running about 10 cfm. Sandblasting is a waiting game, and she never shuts down. I have run 2 5 hp kellog units, and they never get ahead. I would get the largest unit you can power and afford. The blasting units are usually rated for consumption before the tip starts to wear-so under normal use, they will use more. Sounds like single phase is what you have, so I would get a 10 HP unit-even if you have to find your own motor. (10 hp is the largest common motor in single phase). I have had a unit freeze up in the winter and bend the bronze con rods-so I would keep it inside, and run the intake outside. These larger units are usually pretty quiet.
Also, look up spare parts on ecompresedair.com, see what is available.
Joe

I have a 2 stage ingersoll rand type 30. 5HP unit with an 80 gallon tank. I run it at 170psi, and use it about as you're planning to. I bought it new for about $1500 IIRC. I love it, it's got more air than I can use. I have a small blast cabinet that it keeps up with no problem. Its run a DA sander all day, big die grinders, whatever I need. It's rated at 15CFM. I'd recommend this unit.

I would put the compressor in the shop. I live in N.D. Im quessing about the same climate as canada cold. In my experence piping the intake out side and sucking that cool moist dense air in is like dumping a cup of water in the intake. As I stated earlyer Iv never had cold weather starting proplems. But if left in the cold you will have all kinds of moisture problems. Litle air lines like onloaders pressure swithes regulators will freeze with ice. and if useing high volumes of air you actual air line will freeze.

My day job Im a carpenter I work out in the elements in the winter we fight freezing air lines we use Heat the gas atitive. Through the cours of the winter we dump gallons of this through the lines the alchole eats the moisture/ice.

Id be carefully about sticking a compressor out in a cold shed you might be in for trouble. I know people talk all the time about it here but the key is were they live sunny warm south vrs cold north

Enough of this guesswork. Guesswork is silly when simple physics and a calculator will give you reliable numbers. An engineering approach not only saves you money but saves you lost time and frustration. The Internet is full of sites designed to configure compressed air systems for most any service you can imagine from dental drills to blast furnaces to submarine ballast blow. Go browsing.

Start with: determine the demand of your largest air load plus whatever air equipment you plan to use with it. Sum the demand and double it. A reciprocating air compressor running at 50% duty cycle is common conservative practice. If your blast booth is the most critical load you'd best design the compressor system around it. If you use the booth intermittantly for short periods you can size the compressor/mootor combination to a higher duty cycle.

Next is: what is the pressure required. Air pumped to 175 PSI then reduced to 100 wastes energy. The energy lost is not directly proportional but an exponential function I'm too lazy to go into. Suffice it to say if the motor HP is limited don't waste it through a pressure reducer. Energy loss incurred reducing air from 175 PSI to 110 PSI is around 55%. Over half your motor HP is lost at the pressure reducing valve.

Third; are the compressors you are considering two stage? That is does a larger cyinder discharge into a finned heat exchanger which feeds a smaller cylinder? It's a problem in thermodynamics best analogized as "two stage compressors in the blast booth pressure range deliver about 15% more air volume than single stage of similar design."

Fourth: calculate the compressor motor pulley to maximize the motor HP utilization. Calculate pulley sizes for a first trial. Run the system under load actually pumping air. Set the pressure switch to cut in at the lowest pressue acceptable in the blast booth. Set the cut-off to 15 PSI higher. Take a motor load AMP reading. The motor operating current at the instant of cut-off should be 5-10% greater than the motor's nameplate full load Amps. There are sound engineering reasons for this setting; no harm will come to a motor interrmittantly subject to mild overload. If the motor Amps is less than this optimum setting, work the numbers using Boyle's Law and recalculate the motor pulley size. I've used the formulae in Machinery's handbook for 40 years and the couple dozen systems I designed and installed in that time served well, lasting for years of normal service life.

Go not fall in the trap of thinking a large air tank will solve your capacity problem. The greater air storage volume works only as long as the stored pressure lasts then it's the compresser alone that feeds the system.

Engineer it. Guesswork and "an ol' boy tole me..." is for chumps

Thank you for the response.