soft-starting an air compressor

[DJ Delorie]

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?

[Leon]

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.

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?

[DJ Delorie]

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

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

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

[Leon]

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

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.

[DJ Delorie]

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.

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