I’ve not seen one of these on an exhaust for a good while now but what are they and what was their purpose?
It’s to stop rain or debris going down the exhaust pipe when the fumes aren’t pumping out.
and they wear and rattle and clank about and get annoying 
Yeah but you can pretend you’re in the movie DUAL though. 
They weren’t too bad with a ■■■■■■■ as the fast idle kept them open, but with a Roller or Gardner they rattled around a bit. But at least you could tell when the engine stopped… 
Pete.
if you dont have one the rain collects in the pipe then when you start the engine it covers the cab in black smutty patches, and if the sun roof is open you can bet it will come straight in,
Thank god they invented exhaust pipes that point down towards the road
Slightly off topic but the vertical exhausts were first used when ■■■■■■■ diesels became popular in the States during the late '30’s/'40’s, they smoked that much that the police were stopping trucks so they put the pipe up the rear of the cab where it couldn’t do much harm to traffic, only to low flying aircraft!!!
My mate had a Foden with the vertical stack, he parked it up over winter for a couple of month’s when work was slack and then found that it wouldn’t start. I went out to it and found that the engine cylinder head, bores and manifold was full of water, he was lucky that it did no damage because when it finally fired up it was like a hosepipe of water coming out of the silencer, we cured it by drilling a small hole in the elbow at the bottom of the stack.
Pete.
My uncle’s old RAL at the time brand new in this picture which has one.
I remember the earlier FH’s (and FM’s I guess) with Volvo’s own exhaust stack (as that one is by the looks of it^) making a helluva racket with their caps. They were continuously “ting ting ting ting…” on tickover
hotel magnum:
if you dont have one the rain collects in the pipe then when you start the engine it covers the cab in black smutty patches, and if the sun roof is open you can bet it will come straight in,
Thats if your lucky, i have been unlucky twice 
and bent conrods in a merc v8, water doesnt compress very well 
puntabrava:
hotel magnum:
if you dont have one the rain collects in the pipe then when you start the engine it covers the cab in black smutty patches, and if the sun roof is open you can bet it will come straight in,Thats if your lucky, i have been unlucky twice
And here we have the first man to discover hydraulics 
These are the 2 different types of exhaust stacks on my recent drives. In the food industry, they don’t want exhaust fumes in the factory with the chocolate.
The VDB has a rattling flap, the DMT has an angled pipe
