Question about air compressors and unloaders

[macona]

There was enough volume in the line between head and check valve for it to come up to speed without issue.

[J Tiers]

There was enough volume in the line between head and check valve for it to come up to speed without issue.

Not the case here. I thought about adding volume, but decided that was not the actual problem. But with an electric valve and no electric delay it would be essential.

I do know that the compressor will open the check just fine if the leak is blocked.

[rdfeil]

Jerry, I know you are looking at options, but with your low volume compressor a short piece of 1 inch pipe would be a low cost volumetric delay for the compressor. At 1 cfm a 6 inch piece of 1 inch pipe will provide well in excess of 1 second pressure delay. I am not seeing the problem in general...

[Bob Engelhardt]

The bleed-down on shut off can take a long time - as long as it's bled down before the next start. So how about drilling & tapping the bleed hole to take a needle valve that could be adjusted to create enough resistance at start, but still bleed down? Such as (only needs 10-32 hole): https://www.mscdirect.com/product/details/61233136

(Sorry if this is a repeat - I've lost track of this thread)

[JRouche]

I am pretty sure that these compressors are used with tank systems, so there must be an unloader somewhere that will operate with this. I have no idea how this one works, so I do not know if I can modify it (weaker spring?) to do what is needed. I'll maybe take it apart to see.

I found no smaller versions. Anyone know of such?

You would think? I have not seen one though. I would look at Grainger's catalog then MMC. If it not there it never happened. That a small one.

I like those pumps. I have one for an airbrush system. Its noisy so always consider a remote location for it and a small tank. Yeah, no. I still spray right from the pump. It has a better feed then tank air. I know, odd. JR

[J Tiers]

It appears that the maker of the system the compressor is used in is to be responsible for system design. Presumably that includes specifying, or maybe designing the relief/unloader valve.

I suppose it is possible that it just runs all the time, but I think it normally pumps up a tank.

The bleed-down on shut off can take a long time - as long as it's bled down before the next start. So how about drilling & tapping the bleed hole to take a needle valve that could be adjusted to create enough resistance at start, but still bleed down? Such as (only needs 10-32 hole): https://www.mscdirect.com/product/details/61233136

(Sorry if this is a repeat - I've lost track of this thread)

As far as I can see that is not the issue.

The real issue is that the unloader/check valve seems defective. The main flow pass-through holes seem to be drilled in the wrong place, so that when the valve is closed, as it would be before the compressor builds pressure, the pass-through holes actually bypass the large piston, so no pressure can be across it and it will not move the valve. (you can see the design in the model pics above)

I know that is not the intended way for it to operate, since there is another small hole through to the other side of the piston. No sense in having the small hole if the large ones are just in parallel with it.

I don't know for certain if the piston assembly is really drilled wrong, or if the body is wrong, so that the correctly drilled holes are exposed when they should not be. I think it is the piston assembly, because the body seems correctly made for the spring. And, the holes are drilled fairly far back behind the end of the hole through the piston assembly, just about as far back as would cause this problem, and there is room to drill them where I think they should be.

If that extra bypass were not there, the piston could open the check. As it is, the check requires full pressure or more to open it, which will not happen with the leak bleeding air.

Currently I am 600 miles from the shop, so I have time to think about it, and decide what to do.

[Paul Alciatore]

Not returnable? I would call them about that. Most suppliers will take returns with little or no questions.

Actually, some time delay IS needed. The compressor needs to build up speed before the leak closes, or it will just stall. This compressor, anyhow. How long a delay? Perhaps one second. Longer than a valve response time, anyhow.

I DID find pressure switches with a bleed valve in them. Around a hundred bucks just for that. If I have to go that far now, I'll get a different compressor. It will be louder, and provide more air than I want, but............. there is no reason to throw that much money at running this compressor, which is an "it would be nice", and not a "gotta have this" item to begin with.

Still, it seems that the valve I got from Mcmaster has a problem that means it will not and can not work. In some ways it would not matter what compressor was attached to it.

Only one that can build up tank pressure with that leak going will actually work with this valve, and that does not seem to be how it is designed to operate.... so it's defective. it is actually designed to use the large piston to close it, but the defect bypasses that piston (which has a cup seal, so it IS a piston).

Of course I cannot return it, since the defect is only visible with it partly disassembled.

[Bob Engelhardt]

...
create enough resistance at start, but still bleed down?
...

...
As far as I can see that is not the issue.
...

Eh ... sorry for not-relevant suggestion. I didn't keep up and I thought the (only) problem was too much loss when starting. As you were.

[J Tiers]

Eh ... sorry for not-relevant suggestion. I didn't keep up and I thought the (only) problem was too much loss when starting. As you were.

You're fine, I may not have been clear originally.

And it "kinda is the problem", it's just that the root cause is deeper than it seems.