Abstract: Disclosed is a device for loading and unloading modules relative to a pressure vessel and utilized in reverse osmosis systems. The device includes an elongated support for receiving the modules, a fluid actuated cylinder located at one end of the support and a clamp at the opposite end of the support for clamping the support to the open end of the pressure vessel. As each module is disposed on the support, the cylinder is actuated to extend its piston whereby the piston head displaces the module along the support into the open end of the pressure vessel. Additional modules are similarly loaded into the pressure vessel whereby the modules are serially arranged within the pressure vessel.