One possible solution to a buzzing brew valve
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msandford
- Posts: 4
- Joined: 9 years ago
I recently bought and am in the middle of restoring an older Astoria Lady. I got it super used, out of a barn basically and it was not in good shape. I pulled the group heads apart and replaced a bunch of seals and descaled the valves which were literally frozen in place by lime. I don't have any pictures but when I unscrewed the valve guide from the valve flange the plunger inside of all three brew valves didn't move. It took a lot of hot citric acid to loosen them up enough to move so that I could use more citric acid to get them to come apart so I could do it again to really clean them up.
Once I did all that I put things back together and two of the three groups worked fine. But the third one made a HORRIBLE buzzing noise and was shooting water out the group head and down the overflow tube at the same time. I started swapping parts between two of the brew valves to see if I could isolate the problem. I swapped coils, plungers, springs, everything I could think of. What I noticed is that the buzzing followed the plunger, it didn't matter which valve body, coil, flange, or spring I used it was always where I put the one plunger that made a bad valve.
So I checked how magnetic the plungers both were but they were basically the same, at least as far as I could tell with a strong permanent magnet and my hand. I emailed a friend who's got far more experience with everything electrical than I do (despite my EE degree) and he mentioned that if the valve plunger doesn't sit exactly right against the guide seat the valve can buzz. After I did some more research into AC solenoids (they're more complicated than DC solenoids for a number of reasons) I figured that maybe this was the problem.
There's a spring inside the plunger of both valves, and a small hole you can see it through. I used a small screwdriver to push and pull on the spring and it was free in both plungers, so that wasn't the problem. I then got a round, flat bottomed punch and pressed on both of the small red seals on the ends of each plunger. The bigger one on top is fixed in both cases, but the smaller one on the bottom was free to move in one plunger (via the spring) and NOT free to move in the other. This is a development!
The red valve seals press against small protruding orifices; one on the flange and one at the bottom of the valve guide. The top seal is pressed into the top orifice by the external spring when the coil is not energized and the bottom seal is pressed into the bottom orifice by the internal spring when the coil is energized. Except that on the broken plunger, the red seal doesn't move. That prevents the metal plunger body from making contact with the valve guide seat, and this lack of contact (somehow) prevents the valve from working correctly and staying open. From what I gather this is due to the nature of AC solenoids and something called a shading ring that keeps the plunger energized even when the coil is at zero volts.
After putting the broken plunger in a plastic cup with a very strong citric acid solution and microwaving it repeatedly (easier than boiling on the stove) I saw a bunch of bubbles streaming out of the small hole in the plunger. Aha! There's a bunch of scale inside the plunger stopping the bottom seal from moving which makes sense because these things were frozen solid with scale when I first took everything apart. I kept adding citric acid and microwaving until the bubbling stopped and then I was able to move the seal with the punch. This was a non-trivial process involving a lot of taking the plunger out, pressing on the seal, gently tapping it with a punch and a hammer, etc. It eventually budged and stuck at which point I was able to keep working on it and eventually freed everything up.
I then put the valve back together and it worked just fine! Saved myself $50-$100 (and waiting a week) from having to buy either a new valve or a new valve & coil assembly and I get to keep the original parts on the machine. Feels good to fix it and even better to know what was wrong. I think that's the most satisfying part, not having been beaten by some mysterious problem!
Once I did all that I put things back together and two of the three groups worked fine. But the third one made a HORRIBLE buzzing noise and was shooting water out the group head and down the overflow tube at the same time. I started swapping parts between two of the brew valves to see if I could isolate the problem. I swapped coils, plungers, springs, everything I could think of. What I noticed is that the buzzing followed the plunger, it didn't matter which valve body, coil, flange, or spring I used it was always where I put the one plunger that made a bad valve.
So I checked how magnetic the plungers both were but they were basically the same, at least as far as I could tell with a strong permanent magnet and my hand. I emailed a friend who's got far more experience with everything electrical than I do (despite my EE degree) and he mentioned that if the valve plunger doesn't sit exactly right against the guide seat the valve can buzz. After I did some more research into AC solenoids (they're more complicated than DC solenoids for a number of reasons) I figured that maybe this was the problem.
There's a spring inside the plunger of both valves, and a small hole you can see it through. I used a small screwdriver to push and pull on the spring and it was free in both plungers, so that wasn't the problem. I then got a round, flat bottomed punch and pressed on both of the small red seals on the ends of each plunger. The bigger one on top is fixed in both cases, but the smaller one on the bottom was free to move in one plunger (via the spring) and NOT free to move in the other. This is a development!
The red valve seals press against small protruding orifices; one on the flange and one at the bottom of the valve guide. The top seal is pressed into the top orifice by the external spring when the coil is not energized and the bottom seal is pressed into the bottom orifice by the internal spring when the coil is energized. Except that on the broken plunger, the red seal doesn't move. That prevents the metal plunger body from making contact with the valve guide seat, and this lack of contact (somehow) prevents the valve from working correctly and staying open. From what I gather this is due to the nature of AC solenoids and something called a shading ring that keeps the plunger energized even when the coil is at zero volts.
After putting the broken plunger in a plastic cup with a very strong citric acid solution and microwaving it repeatedly (easier than boiling on the stove) I saw a bunch of bubbles streaming out of the small hole in the plunger. Aha! There's a bunch of scale inside the plunger stopping the bottom seal from moving which makes sense because these things were frozen solid with scale when I first took everything apart. I kept adding citric acid and microwaving until the bubbling stopped and then I was able to move the seal with the punch. This was a non-trivial process involving a lot of taking the plunger out, pressing on the seal, gently tapping it with a punch and a hammer, etc. It eventually budged and stuck at which point I was able to keep working on it and eventually freed everything up.
I then put the valve back together and it worked just fine! Saved myself $50-$100 (and waiting a week) from having to buy either a new valve or a new valve & coil assembly and I get to keep the original parts on the machine. Feels good to fix it and even better to know what was wrong. I think that's the most satisfying part, not having been beaten by some mysterious problem!
