So you have put a new solenoid on but it doesn’t seem to be sealing?
Chances are you may have put it on back to front. Yes – solenoids are intended for water flow in one direction only. If you can’t seem to get the water to stop then check the base of the solenoid to see which way the arrow is pointing and if it isn’t in the direction of water flow then you will need to remove it and turn it around.
Another test is to see if the solenoid seals when you turn it ‘on’. Sometimes when solenoids are installed back to front they will stop water flow when the coil is turned to the on position. Either way – get the direction wrong and you will need to dis-assemble and start over.