Update on the Compressor Issues...

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Forum topic by , posted 08-09-2013 12:48 AM 1797 views 0 times favorited 6 replies Add to Favorites Watch
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2387 posts in 2964 days

08-09-2013 12:48 AM

So being cheap, or is it FRUGILE :), I have gone a totally different direction with our Pump issue on our Speedaire compressor. I removed the motor off of the Speedaire compressor and in doing so I discovered the motor pulley is spinning clockwise as I am facing the pulley. But looking at the flywheel on the pump it has an arrow that shows the pump needs to spin counter clockwise. So what I have discovered is the pump appears to have been spinning in the wrong direction since I have owned the compressor, now going on almost 2 years. If what I am seeing is correct, is it even possible to spin the pump backwards and actually get decent CFM, which it always seemed to be pumping good air as it always kept up with our 2 DA sanders. In the end though, the pump went down. I looked and the compressor has a stamp date in 1998, makes this guy 15 years old. However the motor does not look older than a few years old, very new looking. The motor is reversible but is wired for clockwise. I am thinking when the motor was replaced on the compressor, the installer did not pay any attention to the pump direction.

I ended up buying a large industrial compressor at a school auction this week. It is extremely heavy duty and everything checks out good on the pump so far. But it came with a 3 phase motor so I am putting our 7.5 hp single phase motor on it tomorrow and we should be back up and running with compressed air. I have both motors in my truck right now and will be visiting with Belt and Pulley business in San Antonio tomorrow so they can fit me with the proper sized pulley on my single phase motor. In looking at the new to us pump, I discovered the arrow on the pump pulley points to turn counter clockwise that is why I paid close attention to the motor rotation.

Here is our new compressor, it will be plumbed up to our 80 gallon Speedaire tank also to add air storage capacity.

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6 replies so far

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2387 posts in 2964 days

#1 posted 08-09-2013 01:12 AM

I think I may have answered my own question in thinking about this. The piston moves up and down no matter which way the pulley spins, thereby producing air. The reason the pulley needs to spin a certain direction is to pull air into the pulley and act as a fan and blow air over the pump, keeping the pump cooler. The one single symptom we all began to notice over time was that the pump always felt very very hot to touch. We even began aiming a fan at the pump, but the fan was setting on the ground and the pump was up in the air at 6’ so it was probably a wasted attempt at cooling the pump.

Nothing like learning things the hard way.

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View TopamaxSurvivor's profile


17570 posts in 3093 days

#2 posted 08-09-2013 02:01 AM

I’m just an electrician, but I recall a few mechanics and refer guys telling me some things will work in either direction, but run a lot more efficiently with the proper rotation.

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

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2387 posts in 2964 days

#3 posted 08-09-2013 02:14 AM

I agree TopamaxSurvivor. Just think as good as it performed for us, how much better if it had been turning in the proper direction. And if it had been turning in the proper direction and cooling the pump properly, it probably would have lasted for several years longer.

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View dahenley's profile


135 posts in 1510 days

#4 posted 08-09-2013 02:48 AM

not always correct.

this will depend on if it is a single stage or multi stage pump.
if multi stage, then if its not turning correctly then it will not work efficiently and won’t presurise as easy and what not…..
(in my Thermodynamics class, we had to deal with cycles and compressor pumps and what not. but it was all math. no hands on experience so i cant be certain…..)

just out of curiosity, you might just wire it to run backwards and see if it works like it should. (also note. that if someone pulled the big pulley off the compressor and put it on backwards, then it could be working normally but the arrows just be wrong.)

Just something to think about?
( if i could find my book. i could back up my assumptions with statistics and diagrams and information… but its not fresh on my mind currently)

-- David Henley

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2387 posts in 2964 days

#5 posted 08-09-2013 03:00 AM

Thanks Dahenley. I am certain the pump is a multi stage pump. It is crazy to think that the pump could have performed even better than I thought it was. Basically it could fill that 80 gallon tank pretty quickly. I still think if the pulley was in fact running backwards and not blowing air over the pump as would be the design, this would explain why the pump was always so hot. I did not think a lot of the pump being so hot because here in TX it has been very hot and very dry.

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2387 posts in 2964 days

#6 posted 08-15-2013 01:32 AM

So I am still on the air compressor learning curve. For anyone curious or following this I will give the update to what I think I am learning. If no one really cares then I am just documenting for my own fun :)

Well, we got the Quincy compressor at auction. It has a larger pump on it than the Speedaire pump, not sure if larger is better, I do think the Quincy pump is built very well and shows no signs of weakness thus far.

The Quincy compressor had a 5 hp motor, 3 phase that has an RPM of 1740. Since we don’t have 3 phase, I pulled the motor off our Speedaire thinking it was a good motor. Problem is it has an RPM of 3550. I reduced the size of the pulley on my 7.5 hp single phase motor accordingly to ensure the pump was spinning at or near factory setting. The first day things went great. The second day the motor began tripping our 40 amp breaker at start up. I observed that occasionally the motor just did not have enough umph to get the pump going. But yet other times it would get the pump going just fine. The pump by the way has a valve that releases pressure off of the piston after the pressure switch shuts the compressor down. This valve seems to work great, making a very loud hissing noise both at start up and also at shut down.

I gave it much thought and began to conclude that it is possible this motor is just not geared correctly given the faster 3550 RPM spec. I did some looking and began to realize most larger compressors with larger pumps had motors that ran in the 1700 RPM range. I did find that many of the cheaper smaller or inferior models ran motors in the 3600 RPM range. We have a thoroughbred, a great horse we love. So I sort of thought of it as trying to make a thoroughbred do the work meant for a draft horse, or a horse designed for brute power at low speed.

Then a light went off in my head and realized our woodmaster planer has a 7.5 hp single phase motor with RPM of 1740. So we swapped the motor out. And today the Quincy compressor ran like a champ. The breaker never tripped. I am now lead to believe there is an issue with our other 7.5 hp motor. It will spin up fast with no load on it. I bet it would work well in a table saw type of setting.

And if the 7.5 hp 3600 RPM motor is getting weaker, it is maybe even possible the pump that sets on our Speedaire is also fine.

Our solution to all of this. I am following the advice of many fellow LJ and assembling a 10 hp rotary phase converter. Then I will re install the original 5 hp Quincy motor back on the Quincy compressor and run that motor with the 10 hp phase converter. Even though that is a 5 hp motor, it is actually larger in size than either of our 7.5 hp motors.

I also plan to install our 1700 RPM 7.5 hp motor on the Speedaire and run it to see if there are any issues. If it checks out good then I may be able to eliminate the idea that the Speedaire pump is bad.

Hopefully our lessons can provide information to others somewhere down the line looking for Compressor answers.

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