public function purge($maxLifetime = 1440)
	{
		$past = time() - $maxLifetime;
		$query = $this->_db->getQuery(true)
			->delete($this->_db->quoteName($this->_tbl))
			->where($this->_db->quoteName('time') . ' < ' . (int) $past);
		$this->_db->setQuery($query);

		return $this->_db->execute();
	}