Air Assist PSI Reduction Problem

[Ed Maloney]

I have my compressor set at 30PSI but during vector cutting it's showing 10-20PSI. It's been fine for years up until a month or so ago. I removed the hose from the back of the laser and blocked it and the compressor shows 30PSI. Any suggestions how to troubleshoot or if anyone else ran into this?


Ed

[Dave Sheldrake]

It means the compressor cannot keep up with the air requirement.

CFM is displacement FAD is air delivered.

[Ed Maloney]

Thanks for the reply Dave. Don't know what it means though. If I disconnect the hose from the laser and cover the end with my finger, the compressor shows 30PSI. Connected to the laser it is lower.

[Mike Lassiter]

Ed the compressor cannot maintain 30 psi with the volume of air being used. Putting your finger over it and blocking the opening lets it build up pressure due to zero flow. I would look at the filter on it if there is one to see perhaps it is time to clean or replace it. That could be limiting the air the compressor can pump. If no problems there or running it without the filter doesn't change the pressure I believe it is time to look for another compressor.

[Ed Maloney]

Update: I used my old compressor and I still have the same problem.

[Dave Sheldrake]

Pressure depends on nozzle size and displacement of the compressor. To get 30 psi through a 3mm hole you need 16CFM displacement or FAD of 9 CFM @ 60 psi

[David Somers]

Ed....Any chance you have some leaks in the hose from the compressor to the air nozzle on the laser? That could reduce the PSI. And it could account for the fact that two compressors are showing the same problem. The hose would be the common element in that case.

I see the same thing in my vacuum pump on my wood lathe. Every few years I watch the vacuum gauge drop steadily and the cause is typically fittings that have loosened over time, or a hose that is aging and cracking enough to affect the vacuum. The vacuum pump itself chugs along reliably otherwise.

I did notice you are on the Jersey Shore? If you are near enough the ocean you may have some corrosion issues in some valves, or additional cracking in the hoses due to proximity to the ocean. I used to live in Hawaii. I was about 1.5 miles from the volcanic vent on Kilauea and we had some pretty interesting atmospheric gasses to deal with. Acid Rain, sulphur dioxide, etc. The amount of rust that caused in my garage and also exposed equipment was stunning. And rubber stuff died early and unhappy deaths.

[Ed Maloney]

Checked the hoses and didn't see anything obvious. I contacted Epilog via email and am getting nowhere. Guess it's such a rare thing that they may not have any troubleshooting steps to reference.

[Gary Hair]

What are the specs on your compressor(s)?
Tank size:
Motor H.P.:
Max PSI:
CFM:

[Ed Maloney]

It's one of the HF ones that I have been using for years. This problem just started to come up a couple of months ago.

Tank size:
Motor H.P.: 1/5
Max PSI: 58
CFM: .5@20PSI

[Ed Maloney]

Here's the reply from Epilog when I told them I checked all the hoses:

This is a really simply system. Pump, solenoid, air assist tube, brass elbow, air assist tube, brass elbow, air assist nozzle. If you find no fault in the pump itself , it has to be one of these other parts.

[Gary Hair]

CFM: .5@20PSI

There is the problem. As was pointed out in a previous post, you would need 6 CFM at 30 psi with the size hose on you machine. With .5 cfm you'll never get anywhere near that pressure with such low volume. The "problem" has been there all along and you just noticed it - it is impossible for that compressor to have ever put out that pressure.

[Ed Maloney]

There is the problem. As was pointed out in a previous post, you would need 6 CFM at 30 psi with the size hose on you machine. With .5 cfm you'll never get anywhere near that pressure with such low volume. The "problem" has been there all along and you just noticed it - it is impossible for that compressor to have ever put out that pressure.

Hey there Gary. I always glance at the gauge that is on the compressor, especially when cutting acrylic. So my observation is on the gauge showing a lower PSI now, which for the past 8 years has shown 30.

[Dave Sheldrake]

0.5 CFM at 20psi is an airbrush compressor. The only way it could show 30PSI is if either 1: the gauge is faulty or 2: the System is closed (allowing pressure to build up) in an open flow system (air assist) you need at least 3HP+ and a CFM of 14 to get 30psi at the nozzle with a 2.5mm exit hole

[Ed Maloney]

0.5 CFM at 20psi is an airbrush compressor. The only way it could show 30PSI is if either 1: the gauge is faulty or 2: the System is closed (allowing pressure to build up) in an open flow system (air assist) you need at least 3HP+ and a CFM of 14 to get 30psi at the nozzle with a 2.5mm exit hole

Let me first say that I appreciate all the technical details from everyone of what's going on and thanks for taking the time to respond. I purchased a new compressor back in February of this year and the gauge showed 30PSI until recently. My old compressor used to show 30PSI as well.

Let's assume both gauges are incorrect.

So let's say the gauge is saying X PSI. It is now showing a lower Y PSI. What would cause that and how would I trouble shoot it?

I checked the air hoses and don't see anything obvious as far as holes go etc.