Hydraulic Door Systems Hydraulic door systems are the safest transfer systems currently available in the zoological industry. A Thru Z's hydraulic door systems have been proven successful in the zoological indusry and we credit this success to our determination that safety, long term durability, low maintenance, and cost are the priority in planning and installing these systems. If you don't see what your looking for, just ask. Return to Door Systems Main Page Ready to order? Click here