$re = '/^ *\|+ *| *\| *$|(\| *){2,}/m';
$str = '3150779 | 3674-4 |Water Supply Plan
3637730 |
| 10903-155 | Layout 10903 DWG 155 29 M |
| 10903-155 | | Water Supply |';
$subst = "\1";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php