Section 318. Designation of agent for service

A  person  may be
  designated by a natural person, corporation or partnership as  an  agent
  for  service  in a writing, executed and acknowledged in the same manner
  as a deed, with the consent of the agent endorsed thereon.  The  writing
  shall  be  filed  in  the office of the clerk of the county in which the
  principal to  be  served  resides  or  has  its  principal  office.  The
  designation  shall  remain  in  effect  for three years from such filing
  unless it has been revoked by the filing of  a  revocation,  or  by  the
  death,  judicial declaration of incompetency or legal termination of the
  agent or principal.