Selection of Low Temperature Stop Valve

NegotiableUpdate on 05/20

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Overview

The sealing surface of the low-temperature shut-off valve should be flat or conical, and the valve disc should move in a straight line along the centerline of the fluid. The movement form of the valve stem includes a lifting rod type (the valve stem is lifted and lowered without the handwheel lifting), as well as a lifting rotating rod type (the handwheel rotates and lifts together with the valve stem, and the nut is set on the valve body).

Product Details

Selection of Low Temperature Stop Valve

1、 Design requirements for low-temperature valves
According to the usage conditions, the design of low-temperature valves has the following requirements:
1) Valves should have the ability to work for a long time in low-temperature media and ambient temperatures.
2) Valves should not be a significant heat source for low-temperature systems. This is because the inflow of heat not only reduces thermal efficiency, but also causes the internal fluid to flow rapidly if there is too much inflow
Evaporation generates abnormal pressure rise, causing danger.
3) Low temperature media should not have harmful effects on handwheel operation and packing sealing performance.
4) Valve assemblies that come into direct contact with low-temperature media should have explosion-proof and fire-resistant structures.
5) Valve assemblies working at low temperatures cannot be lubricated, so structural measures need to be taken to prevent friction from scratching.
2、 Material selection for low-temperature valves
1. Low temperature valve body material
(1) Factors to be considered in the selection of main materials
From the perspective of metallography, except for austenitic steel, copper, aluminum, etc. with face centered cubic lattice in metallic materials, general steels will exhibit low-temperature brittleness at low temperatures
Sex reduces the strength and service life of valves. When selecting the main material, the first step is to choose a material suitable for working at low temperatures. Aluminum does not exhibit low-temperature brittleness at low temperatures,
However, due to the low hardness of aluminum and aluminum alloys, the wear resistance and scratch resistance of aluminum sealing surfaces are poor, so their use in low-temperature valves is limited to a certain extent, only in low pressure and small diameter applications
Valve selection.
Materials working at low temperatures should ensure their low-temperature performance, mainly by ensuring their cold impact strength. The valve internals must be selected correctly to have sufficient cold shock strength
Degree is necessary to prevent breakage. Alloy steels of C and Cr quickly lose their impact strength below -20 ℃, so their usage temperatures are limited to -30 ℃ and -50 ℃, respectively. Containing Ni
Nickel steel with a content of 3.5% can be used up to -100 ℃, while nickel steel with a Ni content of 9% can be used up to -192 ℃. Austenitic stainless steel, nickel, Monel alloy, Hastelloy alloy, titanium
Aluminum alloy and bronze can be used at lower temperatures (-273 ℃).
In addition, the selection of materials for low-temperature valves should also consider the following factors:
1) The lowest operating temperature of the valve;
2) The mechanical properties required for metal materials to maintain working conditions at low temperatures, especially impact toughness, relative elongation, and structural stability;
3) Has good wear resistance under low temperature and oil-free lubrication conditions;
4) Has good corrosion resistance;
5) When using welding connections, the welding performance of the material also needs to be considered.

Selection of Low Temperature Stop Valve

Features:

(1) The structure is simpler than gate valves, making manufacturing and maintenance more convenient.

(2) The sealing surface is not easily worn or scratched, with good sealing performance. There is no relative sliding between the valve disc and the valve body sealing surface during opening and closing, so the wear and scratches are not severe, the sealing performance is good, and the service life is long.

(3) When opening and closing, the valve disc stroke is small, so the height of the globe valve is smaller than that of the gate valve, but the structural length is longer than that of the gate valve.

(4) The opening and closing torque is large, the opening and closing process is laborious, and the opening and closing time is relatively long.

(5) The fluid resistance is high due to the tortuous medium channels inside the valve body, resulting in high fluid resistance and high power consumption.

(6) When the nominal pressure PN of the medium flow direction is ≤ 16MPa, it is generally used to flow downstream, and the medium flows upward from below the valve disc; When the nominal pressure PN is ≥ 20MPa, reverse flow is generally used, and the medium flows downwards from the valve disc to increase the sealing energy. When in use, the medium of the shut-off valve can only flow in one direction and cannot change the flow direction.

(7) The valve disc is often eroded when fully open.

The commonly used globe valves include national standard globe valves, American standard globe valves, German standard globe valves, Japanese standard globe valves, bellows globe valves, and low-temperature globe valves.