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Help me choose an air compressor for sandblasting and shop.


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#256 NUTNDUN OFFLINE  

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Posted March 05, 2011 - 04:11 PM

I made a video of it running. From 0 pressure to the 135psi cut out. The overall video is 4:14. There is about 40 seconds of waste.



#257 thecoater OFFLINE  

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Posted March 05, 2011 - 04:45 PM

so about 4 minutes to fill to 150 -I would say its safe to say your in the 25cfm range,,what is the total cost on this

#258 NUTNDUN OFFLINE  

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Posted March 05, 2011 - 06:08 PM

With just strictly compressor pieces and not counting anything that I would have needed regardless of what compressor I bought it is just under $1,100.

#259 MH81 ONLINE  

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Posted March 05, 2011 - 06:15 PM

While you were posting the video... I was posting to ask where the video was. LOL

Well Done My Friend! Glad it's working.

#260 RailmanB110 OFFLINE  

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Posted March 05, 2011 - 06:50 PM

Great job... It sounds good too! I bet you feel pretty good about your accomplishment.

Have you had a chance to check the amp draw when the presure is near max?
At 32 amps your right at the max load for that motor. You might want to slow it down just a bit, just to be safe. If you slow it down, the amp draw will drop, & your starter protection will probably hold. At a minimum, I'd check the motor temp when under heavy use. I realise that you're not sure how much air you need, but I'd at least consider slowing it down at a later date to be safe.
Again,
Great job!:worshippy1:
Joe

#261 olcowhand ONLINE  

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Posted March 05, 2011 - 07:22 PM

Good deal George! From here on out, we can truly say you're full of hot air!:rofl2:
Glad all came together. Like Railman said, check the amps near shutdown.

#262 NUTNDUN OFFLINE  

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Posted March 05, 2011 - 07:36 PM

We did check the amps. When it first kicks on it yanks 100 amps for a second or two. When it is close to kick off pressure it was right around 34-35 amps. I will order the next size down pulley and put on it. Should keep me above the minimum rpm.

I can remember what the next size pulley down was.

#263 NUTNDUN OFFLINE  

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Posted March 07, 2011 - 08:14 AM

I ordered the 6.75" pulley for the motor. It should put the pump around 739 rpm. I guess the pump really should have a 10hp motor but I wasn't going to do a phase converter to be able to run one. Once I get the pulley in place we will check the amp load at full pressure and see if we can utilize the overload relay. For the time being we put a 40 amp breaker in place of the 60 amp so the motor does have some sort of overload protection.

#264 olcowhand ONLINE  

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Posted March 07, 2011 - 09:44 AM

Your motor should have a thermal overload protector built in, which will protect it from prolonged overload. Should be a reset button on the motor.

#265 NUTNDUN OFFLINE  

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Posted March 07, 2011 - 09:48 AM

Your motor should have a thermal overload protector built in, which will protect it from prolonged overload. Should be a reset button on the motor.


I am almost positive there is no reset switch on the motor. I will double check it when I get home though.

#266 olcowhand ONLINE  

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Posted March 07, 2011 - 09:52 AM

Never seen a Baldor without the thermal reset.

#267 RailmanB110 OFFLINE  

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Posted March 07, 2011 - 12:29 PM

Overall, I think going to a smaller drive pulley is the right thing to do. I've smoked motors on material blowers running right at their max amps, & it's just not worth the risk. If your planning on doing blasting, you'll probably come near continuous running, & have a good chance of motor overheating. By dropping from the 7 3/4 to 6 3/4 you'll drop about 100 pump rpm, & about 3 cfm. You'll still be around somewhere around 21 cfm rating at 175psi, & have a little margin of safety. If you listen to the video closely, you can hear the motor slowing a bit near the end. With a service factor of 1.15 x 31 amps = 35.65 amps right where your top reading was. The key here is that you plan on running it near continous for periods, & need a margin of safety.
Joe
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#268 NUTNDUN OFFLINE  

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Posted March 07, 2011 - 12:38 PM

Overall, I think going to a smaller drive pulley is the right thing to do. I've smoked motors on material blowers running right at their max amps, & it's just not worth the risk. If your planning on doing blasting, you'll probably come near continuous running, & have a good chance of motor overheating. By dropping from the 7 3/4 to 6 3/4 you'll drop about 100 pump rpm, & about 3 cfm. You'll still be around somewhere around 21 cfm rating at 175psi, & have a little margin of safety. If you listen to the video closely, you can hear the motor slowing a bit near the end. With a service factor of 1.15 x 31 amps = 35.65 amps right where your top reading was. The key here is that you plan on running it near continous for periods, & need a margin of safety.
Joe


I definitely don't want to have to replace the motor anytime soon. Once I get the smaller pulley on I will probably need help figuring out how to wire the overload relay back in to the circuit. The guy that came over and did the wiring did it so fast I didn't really have a chance to see what he even did when we first tried the overload.

I originally plumbed the auxiliary unloader in with the unloader from the pressure switch but I don't think the auxiliary unloader valve is any good anymore. Once I took that out of the plumbing and ran the compressor till it kicked out I tried spinning the motor by hand to see if the pressure switch's unloader was working and it seemed like it wasn't as there was a lot of compression on the compressor.

I don't know when the unloader on the pressure switch kicks in. I don't know if it kicks in right after it hits the cut out or if it kicks in right before the cut in. I would like to have a continuous run unloader setup on it that way if I am using enough air during sandblasting to where the compressor is basically running non stop anyway it would be easier on the motor instead of starting and stopping all the time.

#269 thecoater OFFLINE  

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Posted March 07, 2011 - 12:45 PM

as the compressor shuts down and hits max psi the unloader will kick in and empty the cylinders

with a motor like yours you want to keep the start and stop to less than 5x per hr

so you will want a constant run feature of some sort, I am glad mine has 1 its more like a screw compressor and its easier on the electric motor

my 10hp doesnt have a reset button either and its a baldor,but the 3hp on my spray booth does

#270 RailmanB110 OFFLINE  

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Posted March 07, 2011 - 01:27 PM

If the pressure switch unloader isn't working (assuming it's plumbed right) it may be that you need to add in a one way valve between the tank, & pump. I'm not familiar with the axiliary unloader on your pump.

On my screw compressor, It would operate either in continuous, or start stop mode. When the pump shut down, it did three things.
#1 was the one way valve shut to hold tank pressure away from the pump.
#2 was the unloader valve opened, releasing the screw from start up pressure.
#3 was the intake butterfly/throttle plate closed up.

The intake butterfly is exactly like a carbruator throttle plate.
If any of the three items malfuntioned, the pump would try to start under load.
I've had all three malfunction at different times!




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