namespace :db do
  task import: :environment do
  import_path = "~/backups"
  sql_file = "PostgreSQL.sql"
  database_config = Rails.configuration.database_configuration[Rails.env]

  system "psql --username=#{database_config['username']} -no-password # {database_config['database']} < #{import_path}/#{sql_file}"
  end
end

must be owner of extension plpgsql //and
no privileges could be revoked for "public"

digoal=# copy tbl_join_1 to '/home/pg93/tbl_join_1.dmp';
COPY 10
digoal=# delete from tbl_join_1;
DELETE 10
digoal=# copy tbl_join_1 from '/home/pg93/tbl_join_1.dmp';
COPY 10

pg93@db-172-16-3-150-> pg_dump -f ./tbl_join_1.dmp -t tbl_join_1
pg93@db-172-16-3-150-> psql
psql (9.3.3)
Type "help" for help.

digoal=# drop table tbl_join_1;
DROP TABLE
digoal=# q
pg93@db-172-16-3-150-> psql -f ./tbl_join_1.dmp
SET
SET
SET
SET
SET
SET
SET
SET
SET
CREATE TABLE
ALTER TABLE
ALTER TABLE