Air solenoid on exhaust break normally open or closed

Hi everyone. 

I have and air operated solenoid that allows air a ‘ram’ for lack of a better term to operate the exhaust brake butterfly. 

Looking to purchase a new solenoid. Is what I’m looking for classed as normally open or normally closed?

My understanding is that when I depress the accelerator or clutch the switches break the circuit and the air shuts off as does the exhaust brake. 

Once identified I’d be very grateful for a reliable supplier. 

Thanks in advance. 

Ash

Ash, a solenoid is an electrical device, typically when energised by switches at the locations you mentioned will act like a magnet to open an air valve which in turn operates the exhaust brake. No electricity the air valve is closed. Why are you asking, as in what are the symptoms and what age and make is the truck. Depending on your truck you might need to get a genuine part.

Have you tested the solenoid for continuity? It also my just be stuck and a good spray of Lanox or similar might bring it back to life. Is the solenoid a sealed unit or not? 
If not and you cant find a new replacement then maybe the magyman in SA might be able to repair or reuild it. He specialises in rewinding coils (which is whats inside the solenoid) and get you closer to being back on the road.

Normally closed. Requires power to open the air flow.
Cheers Steve

Hi Mammoth
Solenoid has stopped working. I’ve powered it up but no air flows through.
It’s on a 1973 Denning that had Leyland running gear which I replaced a few years ago. No idea what type of exhaust brake it has. Not a lot of original parts on the old girl.
Cheers
Ash

Hi cobbadog

It’s a sealed unit. Appears to be nothing serviceable unfortunately.

Cheers

Ash

Thanks Steve.

Thinking about this

The solenoid, air side of it, would have to be normally closed
As in not allowing any air to flow when there is no power to the solenoid 

If it was the other way around and the bus had no air the exhaust brake valve would be shut on start up and would remain this way until air pressure had built up

Im not sure if that's what your asking ?

Paul

Yes, it appears it is normally closed. Once power is restored via the switch being let off to complete the circuit the air passes through.
Cheers
Ash

Ash,

What is the problem?