Vacuum control switch

Does anyone know where you would obtain a cheap variable 'pressure' switch to control a 12V motor driving an ex-diesel car diaphragm pump brake
exhauster for loco vacuum brakes? I want to limit the vacuum to 21" Hg, but with the chance to adjust in future.
Steve (Sheffield)
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"Steve" <steveaddyatdsl.pipex.com> wrote in message

switch
Hg, but

Washing machine water level switch. Some only have one port and will only sense pressure, but many are dual port and will sense differential pressure (hence vaccum)
AWEM
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Hmm
Thanks Andrew, I was aware that they sensed pressure to control the water fill, but never thought of them outside washer context. They must be sensitive because I've seen them adjust the level when the clothes have soaked up water on initial fill. Steve
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"Steve" <steveaddyatdsl.pipex.com> wrote in message

'pressure'
brake
21"
will
water
be
have
Usually they have an inverted tube, top end has the sensor, and bottom end sits in the water. As the water rises the pressure goes up and the switch clicks. Common failure mode is soapy gung in tube blocking it. DAHIK !
AWEM
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