I got an older speedaire compressor for cheap that would run but trip the breaker when it got up to high pressure or stopped and restarted under pressure. Saw that it had a 3/4hp motor and figured that was the problem. I got a 2hp motor and rebuilt the pump. After that it was pumping some serious air (doubled the rpm on the new motor). When I hooked it up it short cycled every 5 seconds with the drain open so I replaced the in line check valve from a 3/8 to 3/4”. Now it fills to about 60 psi and then trips the breaker. The output line is also VERY hot. Any thoughts? It’s a 15 amp motor on a 20 amp circuit.
Speedaire Compressor Issues
- Thread starter CDubz123
- Start date
Okay. The motor stops before it trips so I’m leaning towards a pulley size issue. Figured this size motor would handle the load. It’s a 3” drive pulley and 10” pump pulley. It looks like the pump is spinning 1035 rpm now and would be 680 with a 2” drive pulley. There’s no manual for these old pumps what’s typical? Would a 2” drive pulley slip?
Attachments
I dont think thats the orginal motor - its 2 speed and probably from a furnace. That pulley was either what they had, or they used whatever would make it work. 3450rpm is more typical for a single stage compressor.
You'll have a play around some to get it right. Or maybe somebody with a similar compressor can chime in about their pulley size.
You'll have a play around some to get it right. Or maybe somebody with a similar compressor can chime in about their pulley size.
![Compressor_Head_1[1].jpg](/forum/data/attachments/1810/1810891-7ac26c5f9eba4710710d1c66eab71651.jpg)
doubled the rpm on the new motor with a pulley or the motor runs at double the rpm?
c39er
Well-known member
Oh no....Vevor quality issue?
Same pulley new motor is double rpm as the old though.
just a side note, compressor pumps have specs on htem for min/max rpm. too high or too low is not good
That’s exactly what I needed thank you! Looks like I overdid it with this new motor RPM. I way overestimated what the pump rpm should have been. I can remedy it with a 2” drive pulley based off the chart though thank you. it also explains why the 3/4HP motor on it before wasn’t working.
Guess I found that out the hard way.
a good RPM and calculator for pulleys & belts here https://www.blocklayer.com/pulley-belt
Hohn
Well-known member
Glad you were able to resolve this for the most part. I'm writing just to point out that on a perfectly functioning compressor that air discharge is crazy hot, so this isn't really a symptom.
A bit of math shows that multiplying ambient pressure by a factor of 8 (i.e. a pump outlet pressure of 103psi) will raise an inlet temperature of 20C to an outlet temp of about 257C. That's 68F and nearly 500F, plenty hot to turn a good steak into char.
If you are unfortunate enough to have a compressor that's trying to put out 150psi on a single stage, then the discharge temp will rise to ~310C or 590F. That's HOT air. That little copper discharge tube has no chance of dissipating that much heat.
I think about this kind of stuff in the back of my mind when I just consider the mass of whatever pump is on the compressor. A really beefy cast iron pump can absorb a lot of that heat and is slower to rise in pump casting temperature. If you have a really transient pump usage cycle, the heavy pump can absorb and then slowly release much of that heat, which should really enhance pump life in highly transient applications.
Is putting a regulator on this as simple as adding an in line regulator from harbor freight?
www.harborfreight.com
3/8 in. NPT(F) Regulator
Amazing deals on this 3/8In Npt(F) Regulator at Harbor Freight. Quality tools & low prices.
www.harborfreight.com
Attachments
Last edited:
yesIs putting a regulator on this as simple as adding an in line regulator from harbor freight?
3/8 in. NPT(F) Regulator
Amazing deals on this 3/8In Npt(F) Regulator at Harbor Freight. Quality tools & low prices.
as simple as put it where your hose is now, and keep the existing gauge where it is so you have both tank pressure & hose pressure. but you probably have 1/4 NPT pipe , so a 1/4 reg would be easier tan a 3/8
sparkness
Well-known member
the tag on the motor as other have said is too low amperage for a 2HP motor as that import is not that efficient compared to a name brand
86% efficiency of that motor - not possible, more likely 65% which puts that motor at 1.5 HP on a good day
86% efficiency of that motor - not possible, more likely 65% which puts that motor at 1.5 HP on a good day