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PDWA Valves

Pete Lewis

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Pressure Differential Warning Actuator

this is fitted to many 2 line brake systems to warn you of any pressure loss in one circuit which wont be felt on the pedal as loss


many are disconnected, not a very bright idea , but having to connect one up today thought this may be usefull

the spool valve inside is available as a fairly cheap repair  kit  eg robsport sell for £5.7 on ebay complete valve go for silly money

theres little to go wrong apart from O ring failure , so rebuild is a very viable option.

todays  valve is fine just historic disconnection and no harness, which was acquired after much searching, it wont fit , so remove /unscrew switch

the terminals are folded over, so after some poking and twiddling the twin terminals pull out easy, its got two pins siamesed to a central terminal sleeve

so some simple straightening and refit test shows we have a operational switch ( only one terminal is used )

but the warning lamp has been jockeyed into the oil pressure switch , cut that off and run a single earth from lamp to pdwa and its all working fine 

with the valve in situ on a spitfire you need a very slim 3/4" af to unscrew the switch if needs must, it will only leak fluid if the seals have failed.



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As originally fitted at least on the North American cars with dual braking circuits, the PDWA and oil pressure warning light interconnection was an easy and cheap way to provide a bulb check on startup. The ultimate value of that might be debatable, but at least it didn't involve 30 extra feet of wire and three fuses all overseen by a CPU and requiring the services of an EE to diagnose. ;)

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