[Shop-talk] air compressor problem

[Benjamin Zwissler]

Do the compressor and motor turn freely with no load?  13 amps at no load
seems like a lot.

On Dec 24, 2016 1:51 AM, "johnny b" <johnnybh at windstream.net> wrote:

> Season’s Greetings to one and all.
>
> After all of these years of listening, I now have a request from the back
> bench.
>
> I have an air compressor problem.
>
> The compressor is an Ingersoll Rand SS5N5, which is a single stage, two
> cylinder, 5hp electric driven compressor unit on an 80 gallon vertical
> tank. It is rated at 135 psi max., 18.1 cfm @ 90 psi.
>
> I use it in a home shop, mostly light duty.Some weeks, it doesn’t run at
> all.
>
> Originally, I noticed that occasionally the compressor would not come up
> to speed on a restart after tank pressure dropped.When this happened I
> could turn it off and wait a while, then turned it back on and it would run
> normally.In the last month or two, it has gotten to where the compressor
> would run normally only on the first startup of the day.After that, it
> wouldn’t come up to speed.
>
> Today, I started working on it.
>
> I started the compressor with an empty tank.Air temperature in the shop
> was about 60 degrees.
>
> Pump rpm was 990:motor was drawing about 14 amps (I’m using a Craftsman
> clamp on type meter).
>
> At about 60 psi, rpm had dropped to 960, and amps increased to 20; motor
> was noticeably working harder.
>
> At 100 psi, rpm was at 870 and amps were at 22.5.
>
> At 120 psi, rpm was about 800 and amps were at 23.5.At this point the
> belt was beginning to slip so I turned the compressor off.Data plate rating
> for this motor is 22 amps.
>
> I immediately removed the tube from the compressor head to the check valve
> and restarted the compressor.
>
> With no load, rpm was 1001 and amp draw was 13.It ran this way for several
> minutes with no sign of problems.
>
> The temperature at the bearings on both the motor and the pump was 80-85
> degrees.
>
> The motor was replaced in June with a comparable new unit.The pressure
> switch assembly was replaced at the same time.The oil was changed about 2
> months ago.It has always used IR Synthetic Compressor Oil.
>
> Today, I removed the check valve and it was clean and operated freely.The
> unloader valve sounds as if it is working correctly.
>
> So, what else can I check?
>
> Thanks for listening,
>
> johnnyb
>
>
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