How this circuit works?

[karesz]

...
when Solenoid is in hold state, what is the current consumption?...

You see; nobody can tell it for you_except the right datasheet! Thats life_sorry
Generell is to say: Relays/soleonids need mostly a portion (maybe 50...70%) for hold current from switching one, but how many percent in reality it is_is a good question...
Than be care plse with an experimentally received & beautyful value from i.e 50%!
For full functionality you have to check in extrems too; as supply tolerancies/ positions of your equipment(horisontal/vertical or even some angle will be more critical) and temperatures & vibrations/shoves/impacts...
Maybe some interesting articles for these subject: www.solenoids.com/solenoid-technical-data.html
5 Channel Solenoid Monitor IC_ **broken link removed**
K.