New/Old Compressor question

Jordan Baker · #1 19-11-09, 03:06

Hi all

My uncle picked up an old compressor from work that was being thrown away. its a huge tank (60gal.) and the compressor part is a double piston type that turns at 1100rpm.

However he said it had a very old electric motor on it that was shot. We'd like to set this up for use on the farm and so that I can sandblast with it. What we were thinking was to use a gas engine instead so that it could be moved around that farm as the need arises.

Can anyone suggest what kind of engine and the HP that would be needed, also, how does one hook it up so that the engine throttles down when the air insn't being used.

Thanks for any and all help.

Alex Blair (RIP) · #2 19-11-09, 04:01

Quote:

Originally Posted by Jordan Baker

Hi all

My uncle picked up an old compressor from work that was being thrown away. its a huge tank (60gal.) and the compressor part is a double piston type that turns at 1100rpm.

However he said it had a very old electric motor on it that was shot. We'd like to set this up for use on the farm and so that I can sandblast with it. What we were thinking was to use a gas engine instead so that it could be moved around that farm as the need arises.

Can anyone suggest what kind of engine and the HP that would be needed, also, how does one hook it up so that the engine throttles down when the air insn't being used.

Thanks for any and all help.

Jordan
That would require at least a 7.5 HP electric motor or a 10HP gas engine to drive it..an 8HP maybe but you would be better off with something like this,and use the old tank paralleled to it for storage capacity..
Would have to be wired in but on a small trailer and a couple of different plug in points or areas could make a nice unit..
At least with this unit it has all the governors already on it and the whole set up is plug and play..

http://www.canadiantire.ca/AST/brows...Compressor.jsp

cletrac (RIP) · #3 19-11-09, 04:29

Alex, 11.5 cfm @ 90 psi won't run a sandblaster. I have trouble imagining that small an electric motor putting out 7 hp too. One of those heavy 5 hp electrics will run a 20 cfm compressor with no problem but you need a fairly small nozzle in the blaster for it to keep up. I have a 7.5 hp electric on a 35 cfm V4 unit that keeps up with no problem, but one of this size is $3000 at Princess Auto.
An 8 or 10 hp gas engine will replace a 5 hp electric motor and should run almost any normal two cylinder compressor.

cantankrs · #4 19-11-09, 06:09

Hi Jordan,

One way might be if you have a tractor with rear PTO and maybe 3 point linkage, you could rig the compressor to drive off the PTO via a standard drive shaft. That way it could be disconnected when the tractor is required elsewhere. Diesel tractor for economy. Have the tractor upwind so it doesn't ingest the dust. The tractor would barely work with such a small compressor. Maybe find a bigger compressor unit and reuse the 60gal air receiver? The bigger the air receiver the more pumping to fill it and keep it up. But the bigger the receiver the more chance the air has to:
a) cool down, which also
b) causes more moisture to condense out of the air.
which means dryer, cooler air for blasting which allows better efficiency and a better result.

Regarding idling when tank is full - I had to repair the pressure switch on my fairly small cheapo electric direct drive compressor as it was leaking air and I found it had a bit of sheet rubber as a diaphram that tank pressure caused to push against a simple broad faced piston that in turn was restrained by a coil sping with an adjuster nut. (The leak was a split in the rubber so I replaced it with a square cut from a truck inner tube) The spring restricts the travel of the piston which operates mechanical arms to an electric contact switch thus cutting off the 240V AC supply to the motor. As the pressure in the tank drops the piston moves back and the switch gets reset restarting the electric motor. Maybe that action offers some ideas. Bear in mind that AC switch contacts may get burned away quicker under DC usage. Maybe the piston could push on an oil filled tube that works another piston at the other end...
Taking that idea further, I know a chap who years ago was involved in building a ground glider tug from Staghound bits. He told me that the winch was able to pivot toward the tow and thus pushed the actuating rod of a brake or clutch hydraulic master cylinder that fed direct to a fluid pressure guage on the dash that he had recalibrated into load readings so they wouldn't snap the towline.

Regards

Alex McDougall

Alex Blair (RIP) · #5 19-11-09, 15:42

Quote:

Originally Posted by cletrac

Alex, 11.5 cfm @ 90 psi won't run a sandblaster. I have trouble imagining that small an electric motor putting out 7 hp too. One of those heavy 5 hp electrics will run a 20 cfm compressor with no problem but you need a fairly small nozzle in the blaster for it to keep up. I have a 7.5 hp electric on a 35 cfm V4 unit that keeps up with no problem, but one of this size is $3000 at Princess Auto.
An 8 or 10 hp gas engine will replace a 5 hp electric motor and should run almost any normal two cylinder compressor.

You are right..I was looking at the horse power requirements rather than the CFM requirements..if he is using the old compressor..an intercooler between compressor stages,I assume the old compressor is two stage(One big piston,1st stage,..one little piston,2nd stage)
And an intercooler between tanks should keep the final air quite dry..Don't forget to pipe your product air(Intake)to a clean source of supply..away from the contaminated area..

rob love · #6 19-11-09, 16:03

Princess auto sells the unloader valves which also have a bowden cable which will go to the gas/diesel engines throttle. It will put the engine to idle and exhaust any air the compressor builds after a predetermined point is reached, then it will put the engine back to full rpm when the min pressure is reached. Check out any of the wheel barrow type portable compressors at princess and they will have this on them.

Look for one of the kohler or wisconsin engines on the end of grain augers. The augers often sell at auction for rediculously low prices (often $35 to 50, but I have seen them go for $5).
You may have to tinker a bit with the pulley sizes to get the proper rpm on the compressor head.

Jordan Baker · #7 19-11-09, 17:18

Thanks for the replies, We will take a look for one of those auger engines. That sounds like the best way. I saw those partst listed on the Pincess Auto web site.

Will let my uncle know about it all.

Paul Singleton · #8 20-11-09, 00:40

Hi,

If I recall correctly some of the older Honda gasoline compressors used an electric clutch controlled by a standard pressure switch. The pressure switch also controlled a solonoid to pull the throttle when it was time to build air.

Paul

Bob Carriere · #9 20-11-09, 03:29

We have been using the big 10HP electric 2 stage compressor from Princess tied to a 100 pounds pot also from Princess. Draws around 65 amps on start up.... lights have been seen to dip in the village.

It is rated at 30+ cfm at 125 psi with an 120 gallon tank. The tank is set at 175 cut off..... regulator on the line set at 125...... under full blast ....pressure drops to 100 pounds and the motor runs steady.

On Summer days after 3 to 4 bags with minimal breaks for reloading it ( one bag per load) it over heats and needs resetting......or more time to cool down........ we even use a 24 inch electric fan for extra cooling......

It ran fine when we were using a 3/8 line to the pot..... when we switched to a half inch rubber line directly from the one inch steel line to the pot ...we reached it's limit.

After a typical half day of blasting you can drain over 3 liters of water from the tank.

The best home made set up I have seen was a tractor PTO driving an old rotor type compressor as used for jack hammers... the engine was shot and had been removed and was driven by a large MF diesel tractor... probably over 100cfm at 100 psi and using regular beach sand. They would do antique farm equipment such as an old Cockshutt manure spreader in less than an hour.

The dust was unbelievable.....

My conclusion is that if you are to do a whole vehicle...... get a contractor to come on site and do it quickly..... in the long run it is probably cheaper.

Use a medium size compressor unit to do smaller parts and small sub assemblies....and take breaks after reloading......otherwise most shop compressors are not meant to withstand the tremendous demands
of serious sandblasting.

I have done my C15a piece meal with my compressor....but would not do it again...... the next vehicle or trailer will be done by a large mobile unit.

Just for laughs.... it takes over one bag of 80 pounds white quartz sand at $10.30 a bag to do a pitted CMP rim...... cast iron like tranny cases are easier.... pitted sheet metal is also very consuming... one weekend without pushing ourselves Rob and I went through 20 bags.....$180 with tax.... doing a few rims and the front sheet metal for my cab 11... not the whole cab..just the nose sheet metal. Total time about a full day.....

...but we had fun !!!!

BooBee

Jordan Baker · #10 20-11-09, 04:49

Well my plan was to set it up to run my sandblasting cabinet I got from Prince Auto. So im thinking that what ive got now should be more then fine to use.