Frankenstein compressor piecing

[niget2002]

Hello all.

I have another thread where I discussed getting a free tank and a free pump:

https://www.garagejournal.com/forum/showthread.php?t=458973

The tank has been pressure tested, so I'm good to go there. I'm slowly piecing the rest of the parts together. In that thread, we discussed the motor I would need. The plan was to find a 220v 5hp motor. The pulleys I have on hand came off of a 5/8" shaft.

My neighbor offered me a free motor. It already has a 3" double-v pulley on it, whereas the pulley's I have and belt I have are multi-spline ( I think that's what it's called ). The other issue is the motor is only 1725 rpm. It is a beast of a motor though and has oiled bearings.

Playing around on a pulley/belt calculator : https://www.blocklayer.com/pulley-belteng.aspx

I believe I can still use this motor by simply getting a new pump pulley of an appropriate size. Punching in all of the values and shooting for a ~880rpm pump speed, it looks like I just need to get a single or double v-belt pulley that is 5 7/8" in diameter for the pump.

Can someone help me do the math on that and make sure my thoughts are sound before I drop the money on a new pulley?

The original Pulleys I have are 2 9/16 motor - 10" pump.

 

[niget2002]

Well. Nevermind...

I can't seem to read stuff correctly lately. The motor plate states 220v @ 5amp... and right above that it states it's only a 3/4hp motor.

It's still a massive motor... just not the HP I'm looking for. Looks like I'm back to searching.

 

[Citation]

What do you know about the pump? My guess is that is the sort of pump normally found on a 3hp compressor. Do you know the original motor pulley diameter? Your new motor is 1/2 the RPM of the motor that (if I'm correct) would typically be paired with that pump. If I'm correct then the correct pulley size is simply 2x the original diameter.

You didn't say it here but I see that the original belt is a multi-groved belt, not a single V. You should look to see which pulley is cheaper to replace.

You might consider trying to trade/sell the 5hp motor for a 3hp compressor motor. A 3hp compressor motor is likely to be all that pump can handle, it will typically include the over current/temp protection (the red button on the motor) and at 3hp can probably be directly connected to a pressure switch. Your 5hp motor almost certainly needs a magnetic starter. Generic 3hp compressor motors are under $200 (possibly under $150). That might accept the pulleys you have on hand. A 1725rpm 5hp motor is likely a good one and will probably sell for enough to by a 3hp compressor motor. That's before you consider the savings of not needed a mag starter.

 

[Citation]

Well. Nevermind...

I can't seem to read stuff correctly lately. The motor plate states 220v @ 5amp... and right above that it states it's only a 3/4hp motor.

It's still a massive motor... just not the HP I'm looking for. Looks like I'm back to searching.

Well that might make my selling suggestion less attractive!

 

[DeeKay]

I think you need around 5-7/8" driven pulley if you want to use that motor. You just need to find out what trade size v-belt that 3" pulley takes.
You should be fine with that free motor you got, 1800rpm motors make about twice the torque as an equivalent HP 3600rpm motor. If it was the other way around you *might* have had problems..maybe. Other good news, if you ever have to replace that motor, 1800s are usually a bit cheaper than 3600s.


Just saw your recent post nvm what I said!

 

[niget2002]

What do you know about the pump? My guess is that is the sort of pump normally found on a 3hp compressor. Do you know the original motor pulley diameter? Your new motor is 1/2 the RPM of the motor that (if I'm correct) would typically be paired with that pump. If I'm correct then the correct pulley size is simply 2x the original diameter.

You didn't say it here but I see that the original belt is a multi-groved belt, not a single V. You should look to see which pulley is cheaper to replace.

You might consider trying to trade/sell the 5hp motor for a 3hp compressor motor. A 3hp compressor motor is likely to be all that pump can handle, it will typically include the over current/temp protection (the red button on the motor) and at 3hp can probably be directly connected to a pressure switch. Your 5hp motor almost certainly needs a magnetic starter. Generic 3hp compressor motors are under $200 (possibly under $150). That might accept the pulleys you have on hand. A 1725rpm 5hp motor is likely a good one and will probably sell for enough to by a 3hp compressor motor. That's before you consider the savings of not needed a mag starter.

In the other thread, someone was able to find quite a bit of information about the pump. You might be right about the 3hp motor running it. The only thing I really know for certain about the pump is that it came off of an Air compressor that had a 5hp motor on it.

I do have the original motor pulley.

 

[metlmunchr]

The pump you show has a poly-v pulley. On a compressor, the pulley is also the flywheel hence the heavy cross section at the OD. You can't simply exchange the pulley on a compressor for some random smaller pulley with a standard pulley cross section. The pump would likely shake itself to death without the flywheel with the most probable end result being a broken crankshaft due to cyclic fatigue.

Sears alone sold about a bazillion of those DeVilbiss pumps with the poly-v flywheel, not to mention other marketers who used the same pump. They were all cast iron up thru the late 70's and cast aluminum like the one you have from that point up until the time when DeV quit manufacturing pumps.

The change from iron to aluminum is roughly coincident with the time when retailers began to blatantly lie about compressor horsepower. I can't say they don't exist, but I've never seen one of those pumps with a legitimate 5hp motor.

Prior to the "horsepower wars", Sears sold a 2hp and a 3hp version of that pump. Same pump on both, with the 3hp version just spinning a bit faster than the 2hp. I bought one of the 3hp ones new in 1978, and it came with a legitimately rated 3hp 15 amp 230 volt motor. If you look at the amperage on current 5hp special compressor duty motors, you'll find they're also 15 amp motors. IOW, they're actually 3hp if they were legitimately rated. A current real 5hp motor will pull 22-23 amps at full load.

The 2hp ones from Sears were rated 7.5 cfm, or 3.75 cfm per hp, which indicates a good match between motor and pump. My 3hp one was rated 9.5 cfm. So you only got 2 additional cfm for the extra 1hp. This says the pump was running at a speed where its pumping efficiency was greatly reduced. About half of that additional hp went to producing air while the other half went to producing heat.

My pump finally died about a year ago, and I replaced it with one of the 3hp replacement pumps from HF. Used a 3.75" pulley on the motor to give the recommended pump speed of 1050 rpm. Motor pulls about 14 amps at the 125psi cutout pressure, and timing the refill from 95 to 125 consistently shows the pump is producing 12cfm, or 4cfm per hp which is indicative of a good match between pump and motor.

Bottom line, there's no point in looking for a legitimate 5hp motor for the pump you've got. It would have to run the pump way faster than the speed the pump is designed for in order to load the motor, and, if the pump can survive the excess speed, the pumping efficiency would be so bad that the only thing you'd get is maybe a couple more cfm and definitely a bunch more heat.

One of the 15 amp 5hp "liar motors" will give you a legitimate 3hp, and that's all the power that pump can use if the goal is making air rather than heat. Or, in the used market, a real 3hp 3450rpm motor (also 15-16 amps) will serve the same purpose.

 

[niget2002]

wow. That's a lot of detailed information. I'm glad I started this thread.

Based on the information you provided, then I think I should be fine with the following motor. I can use the same pulleys I already have. Looking at the plate on the side of the motor, it says it's rated at 17a @220v giving just a bit extra overhead.

https://www.amazon.com/dp/B07DFQR3PB/?tag=atomicindus08-20

There's also this 3hp motor that's rated at 14.7a@220, so I guess it should work too:

https://www.amazon.com/dp/B01FR8BH24/?tag=atomicindus08-20

 

[metlmunchr]

The first one seems to be a bad link. The 2nd one should work fine.

2 things to look for in a motor would be internal thermal protection and the ability to reverse the rotation. The WEG motor you linked checks both those boxes.

 

[niget2002]

The first one seems to be a bad link. The 2nd one should work fine.

2 things to look for in a motor would be internal thermal protection and the ability to reverse the rotation. The WEG motor you linked checks both those boxes.

Thank you for looking... Here's the link to the first one that should work now

https://www.amazon.com/dp/B07DFQR3PB/?tag=atomicindus08-20

(I also fixed the link above)

I'll probably go with the second one. It's the cheaper alternative too.

 

[metlmunchr]

I'll probably go with the second one. It's the cheaper alternative too.

That's the way I'd go too. If you look at the various images, the first one isn't reversible. IIRC, it is the correct rotation for the pump you have, but down the road you might need to replace the current pump and having the ability to shop without being locked in to a specific direction of rotation would be a plus.

 

[Bert_]

Weg is a good motor. I'd buy that over an off brand.

 

[niget2002]

Thanks again guys. Weg motor has been ordered.

Surprisingly enough, the motor is the first large piece of the air compressor I've had to purchase. The rest of the money spent so far has just been on odds and ends to plumb everything together.

 

[niget2002]

It lives!

I have a small leak where the pipe goes into the tank. I'll need to get that fixed.


Sent from my LM-G820 using Tapatalk

 

[The Cobbler]

looking good!

 

[DeeKay]

nice job! looks good

 

[redmondjp]

Is there a tank check valve at the inlet to the tank? Usually the tank inlet check valve has the port on it for the 1/4" diameter unloader line that goes to the pressure switch, which on your compressor is connected right at the head of the pump (very unusual).

It almost looks like to me that the check valve has been installed backwards on the outlet of the pump, as that fitting setup is usually seen right at the inlet to the tank.