Air compressor help

[joshm]

I'm a current member but Tapatalk forgot all my info so I'm not exactly new.
I picked up a used Emglo LU air compressor a year ago and I'm having issues with it. Was thinking y'all could help a guy out. It's used and the previous owner installed a GE 3 hp electric motor on it. I just recently set it up to fill a 60 gallon tank and it seems that the thermal overload is kicking it off before it will bring that up to the 125psi shutoff. Here is the plate off the GE motor
It's a big heavy motor with a 1.25" pulley shaft. But I'm thinking size might not matter. Lol. I'm running royal purple oil in the 4cyl compressor and it seems to be operating correct. But it still takes a few minutes to pump the 60 gallons up to 90psi where it shuts down. Then when it try's to kick back on the the compression stoke is to much for the motor. It buzzes a second then kicks back off. I can get it all up to 125 but it takes shutting off the big tank and bleeding off the small tanks then opening it all back up once it's running again. Clear as mud I know. Help me! Bigger motor? Maybe pulling the motor and sending it off? Thanks in advance.


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[joshm]

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[sld961]

Is your check valve in the tank working? What size flywheel and what size pulley is on the motor? Maybe you're over working the motor and need to drop the pulley size? I run an L with a 3hp. It's the same as the LU, but without the unloader. Also, maybe the unloader isn't working? Yours looks like mine, motor and all. Here's mine before and after.

Edit: why does it shut down at 90 psi, then try to go to 125?

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[joshm]

It shuts down because the thermal switch in the motor kicks it off. I'll go measure the sheaves


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[joshm]

Compressor sheave is 10" and the motor is 5.5" I'm not using the unloader. Should I be? If it gets to 125 it'll decompress and the cylinders, but if trips out at 90 or 100 the cylinders are still under pressure and there's not enough torque to turn it at start up. I guess if the unloader is running it would have a little momentum to help with startup torque.
Edit. I confused unloader valve with air clutch. Unloader is working at 125 psi shut off. Mine is equipt with a air clutch too. It'll kick off and allow the compressor pulley to keep running.

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[joshm]

That's a nice setup by the way. I'd like to get mine off the hotdog tanks eventually. How does the base hold up. I was thinking about getting a steel plate for a new base. Wood would save me some time and money if it'll work.


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[redmondjp]

I'm thinking that the motor drive pulley is too large - you can confirm this with the use of an AC clamp-on ammeter to see what the motor current is at shutoff. My guess is that the motor is being overloaded.

The other way to do this is to get the pump specifications and see what HP is required at its current speed.

 

[joshm]

Specs for pump are 21.5 cfm @105 psi w/3hp motor. Min rpm 450 max 945. My calculations put it running at 954 rpm. I'm using it to run a medium **** blast gun in cabinet. 10-15 cfm @ 80-100 psi. I'm running it at 60 psi.
I'm loosing efficiency somewhere either in a wore out motor or compressor pump. I can get a rebuild kit for compressor for 140.00 and replace everything. But if it sounds like the motor is running weak maybe I should start there first.


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[md21722]

21cfm... is maybe the displaced, definitely not delivered air supply.

What temperature is the motor getting to? Are you using at 10-12 ga wire? What is the voltage at the motor?

A tank check valve, and pressure switch with unloader tied to check valve is typicalled used in Start-Stop operation.

In Constant Run, the head has unloaders tied to a pilot valve.

There is no "clutch"

Yours appears to be dual crontrol.

 

[bsaint]

Specs for pump are 21.5 cfm @105 psi w/3hp motor. Min rpm 450 max 945. My calculations put it running at 954 rpm. I'm using it to run a medium **** blast gun in cabinet. 10-15 cfm @ 80-100 psi. I'm running it at 60 psi.
I'm loosing efficiency somewhere either in a wore out motor or compressor pump. I can get a rebuild kit for compressor for 140.00 and replace everything. But if it sounds like the motor is running weak maybe I should start there first.


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Using this site to find a pulley size around 500 RPM,

http://www.blocklayer.com/pulley-belteng.aspx

It seems you need like a 3" pulley.

3hp is probably the smallest HP this pump is rated for. So I would shoot for RPM at the bottom of the range to be safe. Sure you could sit there with an amp clamp and change out pulleys, but that gets expensive.

 

[md21722]

The L/LU are 2-3 HP compressor pumps. At 3HP, specs say 100 PSI operation 945RPM with a 5.2" sheave & at 150 PSI operation it is rated 882RPM with a 4.8" sheave. Displaced CFM is around 20-21 CFM, which would translate to about 14 CFM delivered. So 5.5" is too large unless you turn the pressures down. You are likely running into the service factor of the motor. The compressor may have operated OK with the hot dog tanks, but the longer run time of the added external tank is probably causing your issue. So you'll just need to slow the pump down, or turn the pressure down. Specs are in post 16 in this thread http://www.garagejournal.com/forum/showthread.php?t=312047&showall=1.

 

[sld961]

That's a nice setup by the way. I'd like to get mine off the hotdog tanks eventually. How does the base hold up. I was thinking about getting a steel plate for a new base. Wood would save me some time and money if it'll work.


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Thanks. The wood was just for testing and rolling it around the shop. It's on a 30 gal tank now.


Those specs are displaced cfm. At that high of rpm/cfm, you're not going to be able to get as high psi.

I get about 12 to 13 cfm from 120 to 145 psi with a 3hp. I think I'm drawing close to 20 amps, so I really should drop my pulley size, but my motor is 3500 rpm, so pulley sizes that small are hard to find.



When you're filling the tank, time it and use this equation to figure out your actual cfm.

TANK GALLONS x .536* x PSIG divided by SECONDS

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[joshm]

21cfm... is maybe the displaced, definitely not delivered air supply.

What temperature is the motor getting to? Are you using at 10-12 ga wire? What is the voltage at the motor?

A tank check valve, and pressure switch with unloader tied to check valve is typicalled used in Start-Stop operation.

In Constant Run, the head has unloaders tied to a pilot valve.

There is no "clutch"

Yours appears to be dual crontrol.

You are correct no clutch just unloader. Duel run compressor

 

[md21722]

Right, 945 PSI @ 100 PSI... not 125 PSI!!! The lower the pressure the faster you can spin the pump.

Some manufacturers spec bare pumps at displaced CFM. When packaged as a complete compressor assembly with tank, pump, & motor the compressor is rated at the pumps delivered CFM.

sld961 got the chart straight from Jenny/Emglo who made the pump...

 

[joshm]

The L/LU are 2-3 HP compressor pumps. At 3HP, specs say 100 PSI operation 945RPM with a 5.2" sheave & at 150 PSI operation it is rated 882RPM with a 4.8" sheave. Displaced CFM is around 20-21 CFM, which would translate to about 14 CFM delivered. So 5.5" is too large unless you turn the pressures down. You are likely running into the service factor of the motor. The compressor may have operated OK with the hot dog tanks, but the longer run time of the added external tank is probably causing your issue. So you'll just need to slow the pump down, or turn the pressure down. Specs are in post 16 in this thread http://www.garagejournal.com/forum/showthread.php?t=312047&showall=1.

This sounds very likely. I'm running this on a 10 gauge circuit. So I could go up a little in amps. Do you think this pump could handle a 5 hp motor for the duty cycle I'm asking it?
I'm doing beadblast work as a side business. I use it a hr or two a couple nights a week cleaning automotive resto parts for my day job.

 

[md21722]

I wouldn't recommend running the pump harder than Emglo rated it. Emglo pumps tend to make more air and heat than other brands. A 3 HP at a big box store makes 10-11 CFM. The Emglo is pushing around 14. The pumps are generally 80% duty cycle which means they should not be making air for more than 48 minutes in a 60 minute period.

As sld961 indicated, as pressure goes up, delivery goes down. This is the case with all single stage pumps. After about 110 PSI they have to work a lot harder to make air. If you put an amp meter on it, you will see the motor draw progressively more power as the pressure in the tank increases.

I would put the 4.8" sheave on it and live with the 7.5% reduction in air delivery. It should run without any trips. For long continuous use, I would take advantage of the constant run control if it works. It lets the pump and motor free wheel so they're constantly cooling themselves and also limits the number of motor starts.

GE Tri Clad are some of the best motors ever built. I believe that's a TEFC motor, but it may not be. Are there any vent holes in the face or bottom of the sheave end? TEFC motors cool by blowing air over the motor. ODP motors blow air through the motor. TEFC is superior for dusty/dirty conditions.

 

[joshm]

Wanted to say thanks again for all of your input. I know a ton more about compressors than I did 24 hrs ago. You guys are the best.


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[joshm]

I wouldn't recommend running the pump harder than Emglo rated it. Emglo pumps tend to make more air and heat than other brands. A 3 HP at a big box store makes 10-11 CFM. The Emglo is pushing around 14. The pumps are generally 80% duty cycle which means they should not be making air for more than 48 minutes in a 60 minute period. I would put the smaller 4.8" sheave on and live with the 7.5% lower air delivery rather than move that sheave onto a 5 HP motor, but that's just me.

That's what I'll do.
Got a 4.75 on the way. Should have it installed Tuesday and I'll let y'all know how it goes.

 

[The Tool Tyrant]

This sounds very likely. I'm running this on a 10 gauge circuit. So I could go up a little in amps. Do you think this pump could handle a 5 hp motor for the duty cycle I'm asking it?
I'm doing beadblast work as a side business. I use it a hr or two a couple nights a week cleaning automotive resto parts for my day job.

First off, you can't "go up a little in amps" ie, you can't 'add amps'...the motor draws, what the motor draws. Going to a larger breaker or fuse does not 'add' amps.
Second, if you imagine your pump as a car engine and the motor as a manual transmission it may help you visualize the pump/motor combinations. To achieve the best performance, you need the correct combination of H.P. to load...ie, you could drive your car down the freeway in 1st gear, but why would you as the power avaliable in 1st gear is not needed for the load induced. Your pump doesn't care if it's driven by a 3 H.P motor or a 50 H.P motor, as long as it's run within it's rated RPM range.

Are you sure that the unloader in the pressure switch is unloading when the motor stops? I'd check that first. I would also suggest dropping the pump RPM down to 868 by going to a 5" sheave on the motor.
FYI, I see in the photo that the compressor does have 'Dual Run Controls', and in order to function properly, the pressure switch must be set to cut-out at 10 psi higher (135) than the pilot valve cut-out (should be set @ 125 psi)

 

[joshm]

When pressure gets to 120-125 the motor shuts off and pressure switch hisses for about 5 seconds. So I think it's working. Only when the thermal overload shuts down the electric motor, before the set psi, the compressor stays charged and can't start again. 90 or 100psi. I'll play with pilot valve setting. I really havnt been using the pilot valve duel run setting. I guess I should have.


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[sberry]

It looks like MD did a good job, it needs a smaller pulley. I am not familiar with the exact math especially for single stage but its general to some extent. For 2 stage that motor makes 12 cfm. That's a real motor, about 4 per hp but probably a bit more on single at lower pressure. The 14 I see somewhere on this thread should be about right. I wouldnt "rebuild" anything till I got it working, make sure it really isn't working right before overhaul. Make it work, start looking for another 5 hp unit if you are blasting and I would even consider the both if I was trying to make money at it unless it was dental sized stuff.

 

[sberry]

I would be a Clist shark and improve the pumps up to the limit of what I could get, use or absolutely needed.
I saw a couple American resto shows. At the rates he quotes I suspect they got a bigger comp in the back.
If you are charging for this and actually have any waiting work then its the kind of thing it pays to get on top of fast. You can even use junk if its done quickly, if you are running hours and hours on it then its too small and you might as well go flip the burgers.

 

[sberry]

I agree about switching it on when starting, no point in draining it to kick on before the pump starts. Another tank would help some with that feature.
A 3 and a 5 work well together. I have about 200 gallons of tank on and the breaker off to the 5. I can flip it on before I start for sandblast.
I am always curious when someone does something for money. I have seen a lot of body guys sitting behind blasters don't know **** about it. do you have some experience or training in it?

 

[joshm]

I work at a shop that specializes in Italian cars. We've found ourselves getting a bit of resto work the last couple of years. (67 Mura, Alfa Julieta, 308s and 328 suspension rebuilds and fiats. We were subbing the blasting out to various folks around town. One guy told us he used glass instead he used aloxide. Another stays busy and we won't see a part back for a month. In all cases we were driving to and from to get it done. Our market charges 60-75 hr for this service. 1 hr minimum. I foot the bill for a HF industrial cabinet and used compressor that I hoped would push it and the **** gun.

We now know what we are getting as far as media. ( sand and Ferrari or lambo valve covers don't jive) and I can bring a box of parts to the house and have it ready to finish and reinstall the next day. I'm probably close to even for what I have in it. Plus it nice to have around to refinish 1911s and play with. Wouldn't wanna do it full time but a little cash fine with me.

Edit: my setup isn't near powerful enough to do damage. I find myself searching more aggressive media for tougher dirtier jobs, and falling back to glass for finer detailed work. Only experience/training I have is reading lots and hands on. I feel that's better than doing a "job" and getting experience. I'm actively seeking knowledge and trying to improve my process to what I need to do.
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[sberry]

My specialty blast experience is nil so,,, its with sand. Fine sand,,, like beach is "soft" (320 or so) and is for penetration of rust, it is graded and goes all the way to super blast maybe 80 or larger which is for cutting paint and tuff coatings.

 

[sberry]

We call it super blast, next thing to crushed glass. I have some coarse someone gave me, about half a pallet and have been using a blend, the roughest one.

 

[joshm]

I'm using black beauty medium now for nasty rusted jeep parts. 80psi. I use recycled glass in a medium grit for finer stuff. It breaks down and works on aluminum well.


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[sberry]

Ok. I am always curious about the application and efficiency. You have some idea of the value, good work to farm out from work.
There is a bulk sand plant near here where I can buy tons in boxes for some insane low price.
I don't use it much anymore, I did have a little bench top cab but never used it and finally got rid of the thing. I would just as soon set it all on a pallet and fire up the pot and be done if I got to blast.

 

[joshm]

That's nice that you have a good source of sand. I'm sure you know all the negatives of the sand stuff. I just ordered a little siphone feed gun off of flea bay. I'll use it for body patch areas. I'm already thinking of setting it up with a pot. For outside well ventilated stuff that won't fit in my 4 foot cabinet. I did a ferarri exhaust shroud a week ago, I could get all but the very ends. A pot like yours would have been the ticket to finish up the ends.


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[md21722]

It looks like MD did a good job, it needs a smaller pulley. I am not familiar with the exact math especially for single stage but its general to some extent. For 2 stage that motor makes 12 cfm. That's a real motor, about 4 per hp but probably a bit more on single at lower pressure. The 14 I see somewhere on this thread should be about right. I wouldnt "rebuild" anything till I got it working, make sure it really isn't working right before overhaul. Make it work, start looking for another 5 hp unit if you are blasting and I would even consider the both if I was trying to make money at it unless it was dental sized stuff.

Single stage is around 4 CFM/HP. Dual stage is closer to 3.5 CFM/HP. The difference is that dual stage pump linearly through their rated pressures and single stage "slow down". A dual stage can pump 40-60 PSI at the nearly the same speed it can pump 150-170 PSI. A single stage stops around 150 PSI, and will pump far faster 40-60 PSI than it can at 120-140 PSI. In effect, the stated CFM is the average of pumping 0 PSI-shutoff PSI. This is also why single stage usually have a 40 PSI and 90 PSI rating, but dual stage are usually only rated at 175 PSI. As pressures reach maximum, a 20-30% slowdown in a single stage is not uncommon. When measuring actual output, altitude plays a factor. Here in Colorado at 6,500' we have to downrate anything naturally aspirated that uses air about 25%. The backup generators where I used to work needed to be able to provide 4MW and they bought 2 CAT 2.5MW generators... air compressors & cars also face the same issues. So to get 7.5 HP air compressor performance, I bought 2 5 HP compressors...