[malc9141]

This is mainly for HDi fun.

I've got the Bosch book, and injector diagrams which explains where we seemed to be saying different things.

In the injector, there is the piston. It has rail pressure above and below (ie no net force). When the armature is activated, it opens a valve A above the piston. The piston goes up. The pintle is attached so it also goes up. Fuel squirts into the cylinder.

What closes the pintle? Your valid point. Answer: there are bleeds (choked passages) which allow fuel at rail pressure back in above the valve. The armature return spring is evidently strong enough to shut the valve A off.

A bleed under the piston allows it to be closed with the rising pressure above plus a small spring.

Hope this doesn't sound like telling "my grandma how to boil eggs" - just trying to help.

Malc