So my big shop compressor has two problems.

First, when it starts, it starts suddenly. Enough to startle whoever's
in the shop, which is not just annoying but dangerous.

Second, when it starts, it's now making a squeak sound for a moment as
well as the expected noises. I mean, a LOUD squeak, like it's trying to
rip the pulleys off. (oil level is fine)

So I might as well address both problems at the same time.

The usual litany of questions follows...

Has anyone experienced a loud squeak at compressor startup? I assume
I'll be disassembling the whole drive chain and inspecting everything,
but I might as well have something to look for.

Has anyone tried to soft-start a compressor? I've added hard-start kits
to motors before to avoid current spikes, but nothing designed to ramp
up the speed itself. Is switching to three phase and adding a VFD to
ramp up the speed overkill, or even possible?

On 7/12/2023 6:47 PM, DJ Delorie wrote:
>
> So my big shop compressor has two problems.
>
> First, when it starts, it starts suddenly. Enough to startle whoever's
> in the shop, which is not just annoying but dangerous.
>
> Second, when it starts, it's now making a squeak sound for a moment as
> well as the expected noises. I mean, a LOUD squeak, like it's trying to
> rip the pulleys off. (oil level is fine)
>
> So I might as well address both problems at the same time.
>
> The usual litany of questions follows...
>
> Has anyone experienced a loud squeak at compressor startup? I assume
> I'll be disassembling the whole drive chain and inspecting everything,
> but I might as well have something to look for.

YES! I thought it was more like a bird chirp. The issue was the reed
valve plate gasket failed. The reed valve has a self adhered gasket,
meaning on mine, the gasket and reed valve had to be replaced as a unit.
Relatively inexpensive.

If that leak is significant the squeak could possibly be continuous and
or result in total compression loss of that particular
cylinder/cylinders. A motor may start much more quickly if there is
less or no resistance.

Another thought, the pressure relief valve is not closing after the
pressure is released at shut down. If it remains open there will be a
lot less resistance on the motor. It makes that short hiss when the
motor shuts down. If that valve remains open the motor will go to top
speed almost instantly. It should only remain open for a brief moment
until the motor begins to spin.

>
> Has anyone tried to soft-start a compressor? I've added hard-start kits
> to motors before to avoid current spikes, but nothing designed to ramp
> up the speed itself. Is switching to three phase and adding a VFD to
> ramp up the speed overkill, or even possible?

Another thought, 240 volt motors tend to start with a jolt if properly
wired, because of less voltage drop. Have you recently changed the
voltage for the motor?

Leon <lcb11211@swbell.net> writes:
> YES! I thought it was more like a bird chirp.

I feel for the bird's pain then...

https://www.delorie.com/tmp/compressor-squeek.mp4

I cut out most of the middle parts, but it includes the startup and shutdown.

> Another thought, 240 volt motors tend to start with a jolt if properly
> wired, because of less voltage drop. Have you recently changed the
> voltage for the motor?

Nope, it's been 240 since I installed it ages ago.

On 7/15/2023 7:03 PM, DJ Delorie wrote:
> Leon <lcb11211@swbell.net> writes:
>> YES! I thought it was more like a bird chirp.
>
> I feel for the bird's pain then...
>
> https://www.delorie.com/tmp/compressor-squeek.mp4
>
> I cut out most of the middle parts, but it includes the startup and shutdown.

Have you changed the belt? If so, have you
re-tensioned it?

>
>> Another thought, 240 volt motors tend to start with a jolt if properly
>> wired, because of less voltage drop. Have you recently changed the
>> voltage for the motor?
>
> Nope, it's been 240 since I installed it ages ago.

Any upgrade to any aspect of your electrical supply leading from the
entrance of your stricture to the motor.

This sudden jolt start was/is common with many 3+ hp 240 volt cabinet
saws because of little resistance of mechanical parts.

Leon <lcb11211@swbell.net> writes:
> Have you changed the belt?

No. I suspect it's age-related, I'm just using it more these days. Got
a new CNC machine and the spindle wants continuous air, even when
stopped. So we'll be sitting there talking about the next setup, and
suddenly AIR COMPRESSOR.

The screech-like chirp is new.

> Any upgrade to any aspect of your electrical supply leading from the
> entrance of your stricture to the motor.
>
> This sudden jolt start was/is common with many 3+ hp 240 volt cabinet
> saws because of little resistance of mechanical parts.

The jolt has always happened. It just happens when the shop is quiet
now (see cnc), instead of only when using air tools.