From: morris@grian.cps.altadena.ca.us (Mike Morris)
Subject: Automatic utility shutoffs (long follow-up)
Organization: College Park Software, Altadena, CA
Date: Thu, 3 Sep 1992 07:59:14 GMT

rodman@pkr.asd.sgi.com (Paul Rodman) writes:

>I was thinking about getting an automatic gas shutoff for my house, and
>the though occured to me why not make it myself?

>For the simplest and most foolproof thing I though about just buying a
>solenoid gas valve and hooking it up to a simple 24v transformer. In a big
>quake the power will most likely fail and viola! it shuts off the gas. The
>only thing is I will also lose hot water in a power failure (the furnace 
>needs juice for the blowers anyway and the kit. stove is electric). I could
>always install a manual gas "shunt" valve around the solenoid if I want to 
>override it, I suppose.

>I've heard that these gizmos normally cost about $600, (installed?) and
>that you have to have somebody come out to reset them. Is this true? Could
>you reset it yourself?  If they go in-line after the meter can I buy it and install it myself? (I've done some gas plumbing). How much do they run?

I'm not going to comment on the plumber's prices, but I will make
one comment: if any work gets done on my water main, I'm going to have
the city replace my meter with one that is the same size as the "lateral"
(the name the city inspector used for the line from the water main in the 
middle of the street to my meter), and then a cutoff valve, then a tee
feeding a 1" water faucet, then another cutoff valve, then I'll replace
the line to my house with a 1" (or maybe a 1.5") pipe.  I'm going to
modify the handles so that they can be turned with a regular water
wrench or a sprinkler handle.
If there is a problem in my house after a quake, I can shut off the water
with any of three different tools, then use a 1" hose to put out the fire.
You would be amazed at the amount of water a 1" hose will throw vs a
common 1/2" one...

But that is not the reason I am writing this follow-up...

I was over at a local AM radio transmitter a few months ago on a tour
arranged by the local ham radio club and saw a cute gimmick - an 
automatic water shutoff.  They needed one because a good portion of 
their physical plant was under the level of the water lines, and in an 
earthquake the basement and sub-basement of their unmanned site could end
up under water.

The device was rather cute: a pulse-on/pulse-off valve, a gell-cell pack,
and a microswitch with a ball bearing on it (let's see if my character
graphics is up to this at midnight):

   | <-- concrete wall
   |
   |
   |
   |         -=======-
   |        /         \
   |       /           \
   |       |           |
   |       |           |  <--threaded glass dome (part of the fixture)
   |       |           |
   |       |           |
   |      ||   +--+    ||
   |--+   +-+  |  |   +-+
   |  |     |  |  | <-|------ microswitch - see below
   |  +-----+  +--+   |
   |                  |  <--- industrial light fixture shell 
   |  +---------------+
   |  |         ^^ Hole drilled here for the wires from the switch
   |--+
   |

   The housing was screwed into lead anchors in the wall.
   The wall the prototype was mounted to was vertical, if your's isn't
   then shims can be used to level the housing.


   Side view of mechanism fitted into the lamp fixture housing:

                                ----
                               /    \
   3/4" to 1" diameter -----> |      |
   ball bearing                \    /
         flat washers  --> ===  ----  ===        lower washer may not
                           ===        ===    <-- be needed - see text
			   ----------------\
			180 degree bend --> |
	hinge   plunger                     |
           O--------------------------------/
	   |     I
       +---+-----I----------------+     Long arm, low pressure
       |                          | <-- microswitch.
       |  O                   O   | <--  "O"s are the mounting holes
       +--------------------------+
	   /      /       /   <-- connections to the switch

The earthquake sensor is built in to the housing of an industrial
incandescent lamp fixture that has been gutted out to the basic
casting.  The microswitch is mounted on a pair of small L-brackets.
A good source of this small hardware is model and hobby shops -
especially model railroad shops.
The idea is that in an earthquake, the ball bearing will wobble out of
the "pocket" in the upper flat washer, allowing the switch to actuate.
The ball bearing size and the flat washer size needs to be selected so
the bearing is just barely stable in the washer.  The bearing also needs
to be heavy enough to actuate the switch reliably.
Two washers were needed in the prototype because they were thin and when
one was used the ball bearing rested on the switch arm and was not stable.
The washers were brass and were soldered to the center of the switch arm
directly.
The normally closed contacts of the microswitch were used to connect
the battery pack to the "close" coil of the water valve and to the "off" 
function of the transmitter.  The battery pack had a slow-blow fuse that 
shut off the current to the valve after a few seconds.  A pair of normally
open pushbuttons allowed manual activation both the open and closed coils from 
the battery.  A toggle switch over-rode the automatic transmitter shutoff.

Here's an attempt at a plumbing drawing:

                                 manual             <<<--------
----- to building-------+--------bypass---------     water flow
			|                      |
			|                      |
                     manual                    |
		     shutoff                   |
			|                      |
			|-------solenoid-------+----manual---- to main
				 valve              shutoff


While the prototype switched water, the technique could be used for water,
gas, or electric.  In fact the same actuator/sensor could activate a trio of
cutoff valves/contactors.  By the way, the reason the radio station engineer
used a pulse-on/pulse-off was because he had this personal attitude of not
having something running full-time that didn't have to - at a big radio
station the idle current of a normal solenoid valve (i.e. flow is on as
long as power is on) would have been down in the noise level!

By the way, in case anybody questions why an unmanned radio transmitter
needs full-time water, the transmitters and the dummy load are water
cooled.  The water system always seeps a little, and there is a
"keep-full" valve (same idea as a toilet fill valve, but quite different
in the implementation).  Also if they have an antenna or feedline
failure the transmitter power has to go someplace - it is switched to a
dummy load, which without water cooling would burn up in seconds.

NOTICE:  This has been written up by yours truly and submitted to two 
magazines (that know about the duplicate submissions).
-- 
Mike Morris   WA6ILQ   | This space intentionally left blank.
PO Box 1130            | 
Arcadia, CA. 91077     | All opinions must be my own since nobody pays
818-447-7052 evenings  | me enough to be their mouthpiece...