If the solenoid closes when power is removed.
+48-----Cathode of 1N4007 & solenoid----Anode of the 1N4007 other end of solenoid ----- N.O. Contact----Common contact---- 48 0 Volts.
The relay can be replaced by IRL540 MOSFET:
http://www.vishay.com/docs/91300/91300.pdf
Similar to this image.
TTL is your Arduino, Rg is 220R R2 is 10K
1N4007 across the solenoid as mentioned above.
M is your solenoid.
Common ground between transistor source and Arduino.
