# [EVDL] readjustment issue on Square-D vacuum switch



## EVDL List (Jul 27, 2007)

Hello All,

I have one of those boxy ~5"-cubed Square-D vacuum switches from KTA. I 
purchased it from Ken Koch in the early part of this decade, and I think 
I finally put it into service by 2004 or thereabouts (speedy me!). I 
graduated from unreliable-or-no vacuum assist for my power brakes over 
many years on my VoltsRabbit to having perfectly reliable vacuum assist.

I have a vacuum gauge threaded into a brass fitting junction on my 
vacuum tank, and over the years I've noticed that my vacuum setpoints 
have slowly shifted upwards from my desired 10" for turn-on and 20" at 
turn-off. A couple of weeks ago, I finally got around to trying to 
reset from what had become about 13-15" and 22" (assuming my vacuum 
gauge has stayed accurate, which since it is attached to the tank, and 
that is attached to the same piece of metal as the vacuum pump - Thomas, 
does get shook a little).

The Square-D adjustment, if I recall, has you set the turn-off point 
first, with the large screw or nut. This moves that turn-off point up 
or down, and the differential remains constant. To change the 
differential, ie. the lower, turn-on point, one uses the smaller screw 
to the side.

Using my nifty "leaker" brass fitting with handle, the top point 
adjusted fine, but I was surprised by the amount of turning that got me 
virtually no change for the bottom point. I turned and turned till I 
hit the stop. All I can get out of my differential is about 8" at this 
point, or something like 12" for the low point.

Rather odd, is it not? Has anyone out there experienced this problem, 
and if so, how was it fixed? I would think that there is some kind of 
piston with a spring on a pivot point that snaps when the contact points 
are to be opened or closed. My guess is that there is a fatigue issue, 
perhaps with the spring or pivot point (or however it works), over 
several thousand open-close cycles.

I can let it be the way it is right now, at the expense of a bit of 
extra cycling, but I'd prefer to understand, and if possible fix the issue.

Thanks,
Chuck

PS: Does anyone know where I could get a halfway accurate vacuum gauge 
to double check the one on the tank? $45+ at my local Kragen's seems a 
bit pricey, but maybe I'm being cheap. If it's too cheap, it could be 
as far off as the one I'm testing, say the other way (I need a 
"standard" vacuum to calibrate against). Perhaps I could get my auto 
mechanic to use his gauge, assuming we can get a good seal on the open 
threaded fitting I have for attachments.

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## EVDL List (Jul 27, 2007)

Hello Chuck,

I have the same Class No. vacuum switch you do, but my model number has four 
micro switches in it that four contacts are normally off and four contacts 
that are on.

You can reversed the mechanism in this switch to make it a pressure switch 
which is the same unit for a listed Sq D pressure switch.

First try to switch to another set of contacts and see what happens. If the 
results are the same, then you can take apart the assembly and clean it with 
carburetor cleaner and spray it with silicone lubricate.

If still does not work, remove the differential spring and replace it with 
the same lb force and length with one you can get at a hard ward store. 
Some stores have a spring kit that has a gage to measure the pull at a 
certain length. If not, then have them use one of there spring scales.

One thing to remember, that these micro switches are not design to switch on 
power, only control power. I am using a Borsch 12 volt 70 amp rating auto 
relay that you can get at any auto parts store.

Some relays and contactors when first activated will surge in amps and may 
degrade the micro switch contacts. It is best to use suppressor across any 
of the coils of these devices. The one I am using are in NTE4933 to NTE4999 
which are call Zener Overvoltage Tranient Suppressor which is Bidiectional 
meaning that this diode can be install in any direction across the coil. 
The NTE4933 is the right voltage size for 12 volts which is rated for peak 
voltage of 36 voltage.

Roland


----- Original Message ----- 
From: "Chuck Hursch" <[email protected]>
To: "Electric Vehicle Discussion List" <[email protected]>
Sent: Saturday, July 18, 2009 10:47 PM
Subject: [EVDL] readjustment issue on Square-D vacuum switch


> Hello All,
>
> I have one of those boxy ~5"-cubed Square-D vacuum switches from KTA. I
> purchased it from Ken Koch in the early part of this decade, and I think
> I finally put it into service by 2004 or thereabouts (speedy me!). I
> graduated from unreliable-or-no vacuum assist for my power brakes over
> many years on my VoltsRabbit to having perfectly reliable vacuum assist.
>
> I have a vacuum gauge threaded into a brass fitting junction on my
> vacuum tank, and over the years I've noticed that my vacuum setpoints
> have slowly shifted upwards from my desired 10" for turn-on and 20" at
> turn-off. A couple of weeks ago, I finally got around to trying to
> reset from what had become about 13-15" and 22" (assuming my vacuum
> gauge has stayed accurate, which since it is attached to the tank, and
> that is attached to the same piece of metal as the vacuum pump - Thomas,
> does get shook a little).
>
> The Square-D adjustment, if I recall, has you set the turn-off point
> first, with the large screw or nut. This moves that turn-off point up
> or down, and the differential remains constant. To change the
> differential, ie. the lower, turn-on point, one uses the smaller screw
> to the side.
>
> Using my nifty "leaker" brass fitting with handle, the top point
> adjusted fine, but I was surprised by the amount of turning that got me
> virtually no change for the bottom point. I turned and turned till I
> hit the stop. All I can get out of my differential is about 8" at this
> point, or something like 12" for the low point.
>
> Rather odd, is it not? Has anyone out there experienced this problem,
> and if so, how was it fixed? I would think that there is some kind of
> piston with a spring on a pivot point that snaps when the contact points
> are to be opened or closed. My guess is that there is a fatigue issue,
> perhaps with the spring or pivot point (or however it works), over
> several thousand open-close cycles.
>
> I can let it be the way it is right now, at the expense of a bit of
> extra cycling, but I'd prefer to understand, and if possible fix the 
> issue.
>
> Thanks,
> Chuck
>
> PS: Does anyone know where I could get a halfway accurate vacuum gauge
> to double check the one on the tank? $45+ at my local Kragen's seems a
> bit pricey, but maybe I'm being cheap. If it's too cheap, it could be
> as far off as the one I'm testing, say the other way (I need a
> "standard" vacuum to calibrate against). Perhaps I could get my auto
> mechanic to use his gauge, assuming we can get a good seal on the open
> threaded fitting I have for attachments.
>
> _______________________________________________
> General EVDL support: http://evdl.org/help/
> Usage guidelines: http://evdl.org/help/index.html#conv
> Archives: http://evdl.org/archive/
> Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev
>
> 

_______________________________________________
General EVDL support: http://evdl.org/help/
Usage guidelines: http://evdl.org/help/index.html#conv
Archives: http://evdl.org/archive/
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----------



## EVDL List (Jul 27, 2007)

Hi Roland,

The contacts seem fine and do their switching thing eventhough there are 
no suppressors or diodes on the vacuum pump. I remember Lee recommended 
some years ago to me a spec for a startup voltage suppressor, and I've 
been meaning to get this stuff on there, but it's a thousand-and-one 
little projects on this car, and few of them get done. A real workshop 
would help, instead of having to haul a box full of stuff down to the 
carport and set it up everytime... (gets old). Anyways, the KTA diagram 
(from where I got the switch) I don't recall has any suppressors or 
diodes (not that they're not needed).

So it sounds like a disassembly and rebuild is probably what it's going 
to take. I suspect the spring has fatigued and needs replacement. In 
the meantime, till I get to that task, it will run ok the way it is. A 
new, quieter, pump setup from Metric Mind would also be an option (I 
think those are about $200 and change).

Thanks,
Chuck



> Roland Wiench wrote:
> > Hello Chuck,
> >
> > I have the same Class No. vacuum switch you do, but my model number has four
> ...


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