You can use this alias which let you use the longjump (the orange helmet in Half-Life game) with just one key press. If you dont have the helmet it will exec a “normal” jump. The jump alias is binded to the “space” key on your keyboard. 

// Longjump

alias "+lj" "+duck;wait;+jump"
alias "-lj" "-jump;wait;-duck"

bind "space" "+lj"

Put this alias into your autoexec.cfg config file. Its located in this directory:

steamapps\common\Half-Life\valve\autoexec.cfg