The pressure gauge guards SPM 903, are suitable to protect the pressure sensors against the destroying effects of aggressive fluids; by construction, they warranty as well the ultra-pure fluids not to be in contact with anything else than the synthetic materials. They are mechanically resistant through their design and by the use of high quality plastics with a PTFE coated diaphragm. The process pressure is transmitted to the sensor through a non-compressible fluid such as silicon oil. For mounting a sensor on the SPM guard, the filling with oil is done under vacuum. We propose the guards alone but also, complete assembly including sensor, filling/mounting and guard (on request).