The test method of Level III is the same as that of Level IV. However, the allowable leakage is 0.1% of the rated flow of the valve. Level III is usually used as a pressure balanced dual channel, double seat regulating valve without continuous pressure balance seal, such as O-ring is higher than the standard of ordinary level. The test method of Level II is the same as that of Level II, and the allowable valve seat leakage is 10% of the rated flow of the valve. Like Level III, this level is usually used as a double channel, double seat valve and pressure balance valve without continuous pressure balance seal. Level I When the valve to be tested is designed according to the basic type, the Level I standard allows some amendments to Level II, III or IV, and the test may not be conducted after the agreement between the supplier and the demander is reached.

5. Investigate item 5 of the signal line insulation inspection flow chart. The zero point instability will be formed when the insulation of the signal circuit drops. The signal circuit insulation decline is caused by sufficient reasons, and the insulation decline at the cladding part is caused, but the signal cable and its wiring terminal insulation decline or damage cannot be excluded. Because sometimes the site environment is very harsh, a slight neglect of the sealing of the instrument cover and the wire connection is careless, and the moisture acid mist or dust particles invade the instrument junction box or cable protective layer, causing the insulation to drop. The insulation resistance of the signal circuit shall be checked according to the cable side and the flow sensor side, and tested with a megger. Because the signal cable is easy to do first. The flow sensor is divided into two parts: measure the contact resistance of the electrode surface and the insulation resistance of the U-electrode after filling the liquid and measuring the contact resistance of the electrode surface and the tubes.