Apparatus for impregnating a porous substrate such as wood with a treating liquid including a cylinder which is arranged to be secured to a pressure vessel, a free piston reciprocable in the cylinder and being exposed to the pressure conditions in the vessel, a striker pad and striker rod assembly cooperating with the free piston, a bias spring acting on the striker rod to urge the rod and striker pad in opposition to the fluid pressure acting on the piston, damping means urging the rod against the striker pad, and impacting means for periodically striking the rod, the damping spring having a fundamental frequency differing from the fundamental frequency of the piston-striker pad-bias spring assembly so that the piston delivers variable amplitude energy pulses into the vessel.
CROSS REFERENCE TO RELATED APPLICATION
This application is a division of my co-pending Ser. No. 877,403 filed Nov. 17, 1969 and now U.S. Pat. No. 3,632,409.
A method for injecting a treating liquid into a wood or stone material. The liquid is injected in an initial pressure-applying/injecting step in which the wood or stone material is immersed at ambient temperature in a treating liquid under an initial liquid pressure of 1 to 10 kg/cm.sup.2, and maintained at this pressure for a period of time. Subsequently, the pressure is increased to a final pressure having a maximum value of 50 kg/cm.sup.2. Where wood is being treated, the pressure is raised in a plurality of steps of 5 to 10 kg/cm.sup.2 each, followed by a defined holding period. Where stone is being treated, the pressure is increased in a single step. Finally, the treated material is depressurized over a period of at least 20 minutes.
