The one on the M103 is a canister with a two-nipple fitting on the end. The actual valve is a "flap" that moves in a rotary fashion to cover the hole on one nipple. It's held open by a spring, I think, and closed by current.
they get gummed up from fuel residue and stick closed on deceleration, then fail to open fast enough as the engine slow down, causing stalls. The other failure mode is usually to quit altogether and the idle speed goes way up.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!