Big air compressor that will love you long time

I picked up a fairly substantial v4 air compressor that's slightly used but not used enough to wear the paint off the v-belt groves in the pulley.


I'm thinking it's going to take some power to turn it over under pressure.
It has paper intake air filters, made in USA. It weighs about 80lb and appears to be all cast iron and steel on the outside.
Not sure what I'll power it with. Definitely something portable/mobile probably gasoline and probably not electric.

 

Just picked up a 60 gallon craftsman, claims 6.5hp but more like 3hp, sure is a noisy thing. Run er till she blows then try to rig up another motor on it.

 

Old Emglo K style twins came with 2 different ways to start easy. Used a 1 way valve from compressor to air storage tank and when the unit shut off, the air over the head and in the supply pipe from the compressor to the tank was vented. When the pump motor was supplied power, it also closed the venting in the line. That allowed the pump to turn over a couple times before full pressure was reached and helped get the ac motor up to speed. They also used a "cold start" device, spring loaded pressure release that required the supply line to reach about 20 lbs pressure before it stopped venting and the motor to reach an even higher speed before it was loaded. K was the name of the Kellog air compressor company that perfected it all in the 20's or so.

Usually set pressure by selecting the on/off voltage rating of the pressure sw, usually referred to as a Furnas sw. Expensive but good quality in that brand, Ex are 95/125 for sw off at 125 and back on at 95 and if it has or does not have an unload valve. Had an Emglo at the shop, wired for 220 v, that was locked up for low oil and repaired in 1986. Customer never picked it up. Hooked it up for the shop and wired to the fuse box. Changed oil twice a year, turned on at 8 am and off at 5:30 pm 5 days a week and it was still working fine when I had to quit in Feb 2023' Right voltage, no water, change oil and check filter, and I don't know how long they will run. Motor caps, contacts on start sw on motor, and bearings usually go first, bearings in compressor are splash lubed from compressor piston rods.

Emglo made one with an unloader in the head that allowed it to rotate without pumping air so it would run on a gas engine or electric motor with out starting and stopping, the gas engine ones also kicked back to a high idle when the head was unloaded. Two types of valves used, one supplied air to pistons in pump head the kept intake valves open in kick down, a second type had a release valve built into the sw and bypassed the compressed air from the line and it did not go into the tank, Either one had a way of pushing the throttle back to idle. Emglo used Ford engine blue paint since at least the 1970's and my grand father had one in the early 1940's that was well worn. DeWalt bought them out and of course the parts went from being made in Penn to India, the people in Penn then started to make a compressor named the Jenny that was better than the India DeWalt.

 

IMO It is one of the best designed compressors on the market.

 

I think I found the machine this compressor this came off.
This compressor head is normally sold as a "15.7cfm @100psi" air compressor powered by a 10hp Honda gx340 that puts out a max pressure of 150psi.
I was thinking based on low tech displacement tests I did that I would need at least an 8hp engine to make good use of it at a max of 120psi.
It's got a 16 inch diameter pulley. I probably don't want to run the compressor more than about 1,200rpms. If I stick with a 5 inch pulley that should keep me under 1,200rpm if the top speed of my engine is 3,600rpm.

 

I have a used unloader valve with bull whip I pulled off a scrap yard compressor, it was packed full of dirt, the compressor it was on was ran without air filters.
So I pulled the unloader off and put it in my air compressor junk collection of pulleys, air filters and other associated parts, probably 2018.
In 2015 the last time I bought one I could get an unloader valve with bull whip throttle cable for $50.
Now they're $80.
Hopefully I can demexicanize this one and make it work again, there's no way it was working.

 

Looks like a road service air compressor one sees in the back of a dually.
10 years service should be nothing for that baby.

 

I rigged my 4 cylinder Emglo/5 HP Honda with 2 unloaders and throttle control.
Both are disengaged from start to 60 PSI, then one engages the left pair of cylinders leaving the right pair to continue till 150 PSI.
This gave me a high volume at low pressure for sand blasting, and then above 60 PSI is providing tool pressures. If the pressure drops below 60 PSI the first unloader disengages so all 4 cylinders are working.
These heads were made with the unloaders built in.

 

I just run everything single stage since I never need more than 120psi.

 

I had to laugh at the title of this post "love you long time" used to hear that all the time "Love you Long time GI" Ha Ha many many years ago

 

I'm going to mount it up to a wheelbarrow compressor and power it with a 3,600rpm 3hp motor with a 5 and 6 inch pulley and see how much power it draws at various pressures.
I'll probably take whatever it runs up for electrical horsepower and double when selecting a gas motor.
I wouldn't mind running another predator 459cc.

 

I got some numbers.
I hooked the air compressor up to a 3hp 3,600rpm motor.
The rated speed on the motor is 3,450rpm, more than that and it's being over loaded.
Running the air compressor wide open, that means the compressor head discharge just open to the atmosphere, the motor draws about 9.7amps.
So it needs about 3hp just to turn over with no pressure, turning over about 900rpm with a 4 inch pulley on the motor.
I attached the line but left the 1/4 ball valve condensate drain wide open.
That showed 30psi in the tank, motor amps went up to 17amps, that's 5.3hp, that slowed the motor down to 3,300rpm definitely in overload, air compressor was doing 850rpm.
I slowly started closing the valve but before I could get to 60psi the motor was really starting to grawl and I shut it off.
So it will take 3hp just to spin it then about 2.2 to 2.5hp for every 30psi. It would take just about everything a 6.5hp gas motor has to make 30psi.
So it could easily take most of what a predator 459cc can muster to hit 120psi and the predator may not have the balls to turn that compressor with a 5 inch pulley. I figure going from a 4 inch to a 5 will take about 25% more power.
If I had a 5 inch pulley it could use 3.75hp up to 4hp just to turn it over. Every 30psi will take 3hp to run. Probably more oomph that a predator 459cc can chug out.

 

The HP requirement is log. The first 30 may take 2.2, the last 30 will likely take 4.

 

I wasn't sure if it was going to be linier or not.
For example I was thinking 3hp (no load) + 2.2hp to get 30psi. Then + 2.2hp more to get 60psi so to run 60 psi I would be looking at a total of 7.4hp, then to hit 90psi another +2.2hp for a total of 9.6hp then to hit target pressure it would take another 2.2hp for a total of 11.8hp.
But your saying instead of 3+2.2+2.2+2.2+2.2 it might look more like 3+2.2+3+3.5+4 to get to 120psi?
I was trying to test it at no load, the lowest pressure with the drain valve open which was 30psi and then double the open drain valve pressure which would have been 60psi but I started to lock the armature before I could even get to 50psi. I knew that 3hp motor didn't have a chance to make it anywhere near 120psi, but I figured I would get more than 50psi.
So get a 459cc engine and pulley to match which ought to be somewhere between a 3.5 to a 5 inch pulley.

 

I would guesstimate you will need 7.5 hp for 150 psi from the sounds of it. Air is a fluid, and will require more HP at lower pressures when the pump is moving more volume, but on the back side will also require more HP as the compression ratio rises. This is why there are two stage pumps, to lower that final compression ratio and save some work at the cost of a little less volume. If you can live with 100 psi, you may do OK at 6 HP.
Your pulley ratios also come into play....Spin it faster for quicker fill time at the cost of HP, or reduce the HP and spin it slower. I have an old dental compressor that was 1.5 HP, I dropped the drive pulley from 4" to a 2.5" adjustable sheave that I run fully open with a .5 HP fan motor from a heat pump. It is oil less and used to blow out electronics on the bench, and takes 22 minutes from 0 to 80 psi cutoff with the 5 gallon tank. The whole world revolves around time vs. money ......

 

I know it takes 5hp electric just to make 30psi. That's probably just about everything a 6.5hp gasoline engine can muster. That is if I want to use a 4 inch pulley.

 

Running the compressor on a very nice 65f day the unloaded compressor take an amp less power.
Last time I ran it up it was inside and I rolled it outside in 20f air.
So unloaded semi warmish it takes an amp less or about 1/3 less horse power less.
Putting the 5 inch pulley on and running it in nice 65f air while unloaded it went up to 11.5 amps or around 3.6hp.
The 5 inch pulley makes the discharge put out wind.
The 5 inch pulley unloaded made for right about a 3:1 reduction. The motor was overloaded spinning 3,300rpm and the compressor was spinning 1,100rpm.

 

There are no oil filters on the engine or compressor so change oil every 100 hrs.
Clean air filters regularly.
Compressors generally use 20wt non detergent oil.
Small engines are not so sensitive.
Some detergent oils tend to foam especially with splash lubrication which will eventually escape through the crank case breather.

 

I usually use sae20 ND in the electrics and sae30 ND in the gasoline powered ones. Jenny calls for their own iso100 oil which appears to be a dyed blue ester based 30 weight oil that's like $34 a quart.

 

Found a huge, probably in excess of 300lb beyond worn out devilbliss air compressor with probably a 30 gallon tank.
Has a single phase 3hp, 1,800rpm 184t frame motor that appears to work, much newer than the rest of the machine but it's still probably at least 20 years old.
Obviously the 3hp motor will just go on my spare motor shelf for now.