By nominal pressure:
(1) Vacuum valve: refers to a valve whose working pressure is lower than the standard atmospheric pressure.
(2) Low pressure valve: refers to a valve with a nominal pressure PN ≤ 1.6Mpa.
(3) Medium pressure valve: refers to a valve with a nominal pressure PN of 2.5Mpa, 4.0Mpa, 6.4Mpa.
(4) High pressure valve: refers to a valve with a nominal pressure PN of 10.0Mpa ～ 80.0Mpa.
(5) Ultra-high pressure valve: refers to a valve with a nominal pressure of PN≥100.0Mpa.
When a certain specification of valve is manufactured in batches, an official agency should be entrusted to perform the following performance testing:
① Opening and closing torque of the valve under working pressure;
②Detection of flow resistance coefficient of valve under pipeline water delivery condition.
The valve should be tested before leaving the factory:
① When the valve is open, the valve body should withstand the internal pressure detection of twice the valve's working pressure value;
② When the valve is closed, the two sides bear 11 times the valve working pressure value, and there is no leakage; but the metal sealed butterfly valve does not exceed the leakage value.
There are three sealing positions of the valve: the contact between the opening and closing member and the two sealing surfaces of the valve seat; the fitting of the packing with the valve stem and the stuffing box; and the connection between the valve body and the valve cover. The previous leak is called internal leakage, which is commonly referred to as improper closing, which will affect the valve's ability to intercept the medium. For shut-off valves, internal leakage is not allowed.
The latter two leaks are called external leaks, that is, the medium leaks from the inside of the valve to the outside of the valve. Leakage can cause material loss, pollute the environment, and cause accidents if it is serious. For flammable, explosive, toxic or radioactive media, leakage is not allowed, so the valve must have reliable sealing performance.
Contact Person: Mr. Hanson