Bumping this from the dead.
Ok- everything here is easy and self-explanatory except: Why are you guys using a Valve rated for 24VDC, when our electrical system is 12VDC (most likely regulated down to 10VDC or so)?
I would assume that applying 12VDC or less to this 24VDC coil, means you're under-driving the solenoid (providing full voltage should cause faster valve response and less oscillation).
I don't want to overthink this, but this doesn't quite add up to me.
EDIT: Nevermind. The valve supplier site was confusing, as they stated its voltage rating as 24VDC, even for the 411L3212HV part#. 411L32
12HV dsignates 12VDC. A quick look at their part# designation cleared this up. Carry on

PS: McMaster Carr carries these valves, too. Just at almost twice the price...
http://www.mcmaster.com/#miniature-solenoid-valves/=y2scvy