1. Check whether the positive and negative pressure valve of the pressure difference transmitter is closed or not and the balance valve is open or not. 

2. Open the blow down valve. Slowly open the flushing tube of primary valve, close the blowdown valve after flushing. Generally the numbers of flushing shall not be less than twice. 

3. Only after the tube is cooled, can the instrument be started. If the pipeline is provided with air vent, the air vent shall be firstly opened to exhaut the air, then the instrument can be started. 

4. Open the positive pressure valve of the transmitter gradually, when the measurement medium is steam or liquid, after it is filled with condensation water or liquid, loosen the blowdown screw of the positive and negative test chamber of the transmitter, after the medium escapes and the air is exhausted, tighten the screws, and then check whether there is penetration or leakage, and check the Zero of instrument. 

5. Close the balance valve and open the negative pressure valve gradually.