Unless the parties agree upon a sole arbitrator within fourteen days of one receiving a written request from the other for arbitration, the claimant (the party requesting arbitration) shall appoint its arbitrator and give written notice thereof to the respondent. Within thirty days of receiving such notice the respondent shall appoint its arbitrator and give written notice thereof to the claimant, failing which the claimant may apply to the appointor hereinafter named to nominate an arbitrator on behalf of the respondent.