What could damage an expansion valve like this?

ChrisJ

I can't remember if I've ever asked this on here before, but even if I have I suppose it couldn't hurt to try again.

This is the float valve seat from my 1933 refrigerator. The valve seat is really rough around most of it, and then looks perfect in a small section, just like new. The metal is everdur bronze and I believe the needle is some kind of steel.

This is a high side float which operates by filling and then flipping wide open, and then shutting completely. It doesn't modulate. My guess, was perhaps flash gas?


This is a picture showing how the needle and seat look assembled.




This is a picture I took after cutting the needle guide off to get a close up of the seat damage.





This damage appears to happen to almost all of these refrigerators so it's not a one time deal. The easily solution is to convert it to a capillary tube but we'd love to know why the valve seat gets destroyed like this and all opinions are welcome. I've heard rumors of a few perfectly working float valve machines but have not personally seen them. All 3 of mine have shot valves.

Oh, one detail that might matter, I don't know, is these specific refrigerators have a minor issue with the refrigerant breaking down and producing non-condensable gas. The side effect is this gas gets trapped in the float chamber and holds the float down. Not a lot at first, but as it gets worse it holds it down more and more until it even stalls the compressor. I don't know if this is when the damage occurs, or if it happens anyway. I can't get this information.


I find it really bizzar that mine, as well as all of the others that have been removed appear to be damaged similarly. With damage in some areas, and no damage in others.

I can't help but think the NCG is responsible for it because none of the GE SO2 machines have this issue, only the methyl formate ones do.

Techman

You lucky dog. I have not run across this problem.

JStar

Could that be wire-drawing errosion? Maybe caused by high upstream pressure when the needle is closed.

ChrisJ

JStar said:

Could that be wire-drawing errosion? Maybe caused by high upstream pressure when the needle is closed.

Interesting, I've never heard of that before.
From what I've found so far, it's also called "grooving".

Under most conditions, the highside on these is close to atmosphere, or around 10 PSI at the absolute most. The lowside is typically around 27" to 28" HG.

I didn't think that was that big of a pressure differential?

Here's a picture of another damaged valve seat.

Techman

I think JStar is right w/ the wire drawing,but I'm not sure if it is limited to hi press. Into the library I will go!

ChrisJ, now follow/indulge me for a minute. I think( this is all in my head,so cut me some slack) that going from 24psig down to 0 psig is one thing (24 psi differential) is somehow different than going from 10psig down to 28" vac. That is also a 24psi diff. I think the vac would really suck liquid refrigerant thru pretty fast. Maybe its my cramped brain after the 1st day of Copeland-COSS Class.

bob_46

there is no such thing as suck . Vacuum pumps don't suck they push .

ChrisJ

I don't know.
I kind of thought that too, but I think the reason a 28" HG vacuum seems really strong and hard to achieve is the pump has nothing to pump. Kind of like when you plug the hose on a vacuum cleaner it's motor speeds up and power consumption drops because the fan has nothing to pull.

icesailor

bob said:

there is no such thing as suck . Vacuum pumps don't suck they push .

That's right.

Mrs. Nature hates a vacuum and will do whatever she can to push something into a vacuum to get rid of it. gas or liquid. She doesn't care.

Water pumps, pumping water actually do not pump to move the water, as the water leaves the pump discharge. Mrs. Nature pushes the water up the inlet/suction pipe.

Its the same reason why you never see a lake with water levels higher at one end of a lake than another.

ChrisJ

Please correct me if I'm wrong, but, I didn't think nature had anything to do with what goes on in a closed system?

icesailor

ChrisJ said:

Please correct me if I'm wrong, but, I didn't think nature had anything to do with what goes on in a closed system?

You're wrong.

Mrs. Nature is everywhere. You can't fool her, and don't futz with her. If you don't understand how she works, she will get you.

James Watt didn't invent the Steam Engine to put into a railroad Locomotive. He designed it to replace horses that pumped water out of coal mines in England.

ChrisJ

@icesailor
I didn't realize you worked with refrigeration.
Learn something new every day.

JUGHNE

I think Ice sailor is referring to the things that nature establishes as constants, depending upon where we are on the planet.
Such as atmospheric pressure, ambient air temp, humidity, dew point, wind chill factors and specific gravity of fluids we work with; including the refrigerants we use.

ChrisJ

Here is a video showing the general operation of the float valve.

This is an older series which uses SO2 refrigerant, but I'm told the operation of the float valve is the same though it's construction is a little different. I originally assumed the float valve modulated the flow but apparently that is incorrect.

https://youtu.be/QvJNlpvETA8?t=2m22s

I'm amazed they even made a video like this.

Techman

I love this profession!

SWEI

Looks like 16mm film. Very cool.

The inclusion of (real or not) projector noise was a bit annoying IMO.

ChrisJ

SWEI said:

Looks like 16mm film. Very cool.

The inclusion of (real or not) projector noise was a bit annoying IMO.

Yeah, I just turn the speakers off.
Not sure what that noise is from, my guess is whatever they use to record the film to video has something for audio and since audio wasn't there you get noise instead.

ChrisJ

So after a lot of time I think we figured it out.

@JStar was right, it's wire drawing and it's caused by non-condensible gas accumulating in the float chamber and holding the float down.

GE knew about the non-condensible problem with methyl formate and they did a lot of things to try to fix the problem but gave up after 1934. Moisture left in the system causes it as well as high temperatures. This is why not all machines have damaged valves, but many do. If it was neglected and left to run like that for who knows how many years, if not decades, it got destroyed. If it was bled properly, it didn't.