Sunday, October 23, 2011

The gate latch saga

Here is the gate latch at the main gate to Searock; deceptively innocent and simple looking, but actually a complicated affair involving telephone lines, electrical solenoids, springs, buzzers, and a delicate balance between a positive closure and a heavy wooden gate that sometimes slams (too often) and sometimes stops short of closing (also too often.)
A solenoid built into the latch receives an electrical impulse of about 26 volts when someone enters the correct code on the keypad outside the gate. With a loud buzz, a plate is pulled back within the latch by the solenoid, allowing the latch to swing freely out of the way when the gate is pushed. After ten seconds the voltage is cut and the plate snaps back to prevent the latch from allowing the gate to open.

After a recent flurry of guests (about 50 in one afternoon) the latch stopped stopping! The gate would just bounce against the stone when it slammed, and the gate could just be pushed open at will, even by the wind, and then Gideon
would be out on the highway trick-or-treating.
Having repaired this same latch almost 5 years ago, I wasn't all that excited to take it apart to figure out what was going on, but I could tell things were askew in there and that 'surgery' was indicated. Here's how it looked then, in December of 2006:
After I chipped away the mortar holding the housing in place, got it on the bench and opened it up, I removed the latch/solenoid mechanism and put it in the vise.

The solenoid is in the upper section, the latch in the lower.

The latch is supposed to pivot on a pin when the solenoid pulls the plate back. You can see the head of the pivot pin at the right, protruding out from the side of the assembly. At first, I thought I'd found the problem: the pin had slipped out of its port on the left side of the assembly, causing the latch to sit askew in the housing, eventhough there is an allen screw locking the latch against the pin. It must've come a bit loose. I had to loosen it more, though, to push the pin back into place. When I pushed the pin all the way in, things straightened up nicely. But it didn't look likely to stay, what with all the banging and slamming that the gate undergoes, so I decided to pull the pin and replace it with one I could make stay. Of course I had to also decide I would be able to get that little spring in the middle wrapped around the pivot pin back in place around a new pin. So I pulled the pin, and made a further discovery:
The latch itself was breaking around the pin! in two places! And the pin was bent from the repeated stress of the gate banging against it. So now, instead of just putting it back together, I had to have a new latch. I didn't want to put this one back in service just to have it break again in the near future.
Fortunately, I had a new latch/solenoid assembly with which to replace the whole unit. Unfortunatley, the new unit was in a housing of an entirely different shape and size.

Fortunately I could fabricate a hardwood block into which I could mount the new latch assembly that would allow for future servicing by being removable and yet sturdy enough to hold up to rough duty at the gate.

Things were going well. I took the new assembly out to the gate to test and mount it.
I hooked up the wires and pressed the code into the keypad. "Buzz", said the latch, and I physically operated the latch with my finger to prove it was released by the solenoid. I then proceeded to mount the assembly.
But when I finished and stood back to test it again, unfortunatley it didn't work, no buzz, no nothin'. Partial disassembly and tried the code again..."buzz", okay, we're in business! Reassembly, but then, no buzz, no work!
After removing the assembly once more, I measured the voltage at the gate wire to be 25.9 volts. Checking the rating label on the new solenoid latch I saw this:

"16 to 24 V.AC"
Okay, so I must've burned up my new solenoid with too much voltage. I wonder if I can mount the old solenoid in the new housing?
Fortunately, the old one was still functional and I was able to fit it into the new housing by cutting away some of the steel plate on which the old solenoid was mounted.

The new, burnt-out solenoid is on the right, the old, modified one is on the left; the blue tape is the pattern I used to make the cuts.
The picture further above of the opened new latch assembly is actually the new housing with the old solenoid fitted into it. After remounting the whole thing back onto the gate post, I am pleased to report that it has never worked, or looked, better!


John said...

Congratulations on what must have been a frustrating job. I am glad it works well, of course you now have an additional piece of wood to keep stained, but it seems a small price.

Mark said...

Thanks, John. Yeah, now I need to refinish the gate, too, as it looks so shabby next to that nice block of hardwood. :-)

Jeannette said...

I think there is a world of difference between shab and character. The gate has character.

Dave Arnold said...

Mark, you did an increadible job with this. The addition of the wood block may provide some cushion for the gate closing and prolong the need for adjustment. Great work!