The Types of Valves
1. We should first select valves
with high closure reliability. The reliability of common shut-off valves
from high to low is: gate valves, globe valves, ball valves, plug valves, butterfly valves.
2. Unless there is an requirement on the process, we should give priority to the valves with small resistance. The resistance drop of common shut-off valves from low to high is: ball valves
, plug valves, gate valves, globe valves, butterfly valves. When the tightness of the closure and resistance drop requirements fall in contradiction, the former should be given priority to.
3. For valves used for liquefied petroleum gas and other liquid hydrocarbon, we preferably select valves such as globe valves
, butterfly valves, etc. which will not form closed valve cavities. When choose valves which will form closed valve cavities, pressure relief holes should be set on the valve cavities.
4. Take into account the economy principle at the same time.
The Structures of Valves
1. Unless there are other requirements, we should first select valves
with the standard diameters and valves with the reducing diameters are not recommended.
2. Unless there are other requirements, we should give priority to valves with the welding connection structures, especially when the valve
pressure rating exceeds Class600 (for Class series) or PN64 (for PN series). When the threaded connection is adopted, seal welding should be attached to the welding.
3. Unless there are other requirements, gate valves
with and above DN50 should adopt wedge-shaped elastic valve clacks; globe valves should adopt plug-shaped or spherical valve clacks instead of flat-shaped valve clacks; triple offset butterfly valves or double-offset butterfly valves with high performance should be chosen instead of centerline type butterfly valves; wafer check valves are not recommended.
4. As the residual media will affect the maintenance of the valves
, the venting fluid-discharge system should be set on the gate valves, ball valves, wafer check valves with and above DN1000 and other valves considered by the engineering design personnel as well as production operators which the venting fluid-discharge system should be set on.
5. When we use non-metallic sealed valves
, the valves should not only have the safe fireproof and anti-static structures, but also pass through the fire safety test.
6. The valves should be required to have the anti-leakage designs, and can meet the ISO 5208 leakage class requirements of the C Class or B Class.
7. The valves should be required to have the anti-leakage designs, and can meet the SPE77 / 312 low leakage class requirements.
The Materials of Valves
1. For the materials of the valves' pressure parts, we should select metal materials with high quality. If it is necessary, we can appropriately control surface defects, internal defects, non-metallic inclusions, grain size, etc, especially for valves
with the pressure class exceeding Class600 (for Class series) or PN64 (for PN series) near the hydrogen environment.
2. Cast iron and other brittle materials are not allowed to be used.
3. Bonnets should adopt bolts with high strength and have gaskets with the high gasket factor.
4. The sealing surfaces of the valve clacks, the valve seats and the upper seal should have surface hardening treatment by the method of surfacing hard alloy.
5. The surfaces of the valve stems should have suitable surface hardening treatment to reduce the increasing amount of leakage due to wear.
6. We should evaluate and then determine the adaptability of the valve internal parts' materials, the bonnets' gaskets, the valve stems' packing to the media conditions.