Valve installation knowledge and precautions

Installation requirements for valves

The quality of valve installation directly affects the future use of valves, therefore, it should be highly valued by construction and production units.

The installation of valves should be carried out in accordance with the valve user manual and relevant regulations. During the construction process, careful inspection and meticulous construction are required. Before installing the valve, it must pass the pressure test before installation. Carefully check whether the specifications and models of the valve match the drawings, whether all parts of the valve are intact, whether the opening and closing valve rotates flexibly, and whether the sealing surface is damaged. After confirming that everything is correct, installation can proceed.

When installing the valve, the operating mechanism of the valve should be at least 1.2m away from the operating ground and flush with the chest. When the center of the valve is more than 1.8m away from the operating ground from the handwheel, an operating platform should be set up for valves and safety valves that require more operations. For pipelines with a large number of valves, valves should be concentrated on the platform as much as possible for easy operation.

For individual valves that exceed 1.8m and are not frequently operated, equipment such as sprockets, extension rods, movable platforms, and movable ladders can be used. When the valve is installed below the operating surface, an extension rod should be installed, and the ground valve should be equipped with a ground well. For safety reasons, the ground well should be covered.

The valve stem of a valve on a horizontal pipeline should preferably be installed vertically upwards and should not be installed downwards. The valve stem is installed downwards, which is inconvenient to operate and maintain, and it is also prone to corrosion and accidents of the valve. Do not install the floor valve tilted to avoid inconvenient operation.

Valves on parallel pipelines should have space for operation, maintenance, and disassembly, and the clear distance between their handwheels should not be less than 100mm. If the pipe spacing is narrow, the valves should be staggered and arranged.

For valves with high opening force, low strength, high brittleness, and heavy weight, valve supports should be installed before installation to reduce starting stress.

When installing valves, use pipe clamps for the pipes near the valve, while using a regular wrench for the valve itself. At the same time, during installation, the valve should be in a semi closed state to prevent rotation and deformation of the valve.

The correct installation of valves should ensure that the internal structural form conforms to the flow direction of the medium, and the installation form meets the special requirements and operational requirements of the valve structure. Special attention should be paid to the installation of valves with medium flow requirements according to the requirements of the process pipeline. The arrangement of valves should be convenient and reasonable, and operators should have easy access to the valves. For lift valve stem valves, there should be enough operating space. All valve stems should be installed as upward as possible and perpendicular to the pipeline.

Installation of valve connection surface

When installing valves with threaded connections at the end, the depth of thread insertion into the valve should be appropriate. If the thread is inserted too deeply and presses the valve seat tightly, it will affect the good fit between the valve seat and the gate plate. If the thread is inserted too shallowly, it will affect the sealing reliability of the joint and easily introduce leakage. At the same time, the thread sealing material should use PTFE tape or sealant, and be careful not to apply the sealing material to the valve cavity.

For valves with flange end connections, the first step is to align the flange connection surface, with the cover perpendicular to the pipeline and the bolt holes aligned. The valve flange should be parallel to the pipeline flange, with moderate flange clearance and no misalignment or tilting. The flange center gasket should be placed in the center without deviation, and the bolts should be symmetrically and evenly tightened. Prevent forced tightening of connections during valve installation, resulting in an additional residual force.

Thoroughly clean the dirt on the inner wall and external threads of the pipe before installation; Remove burrs, foreign objects, etc. that hinder the flow of the medium and may affect the operation of the equipment, and blow off dirt, slag, and other debris in the pipeline before connecting the pipes. Prevent damage to the sealing surface of the valve or blockage of the valve.

When installing the welded end connection valve, the welded joints at both ends of the valve should be assembled and spot welded first. The valve should be opened, and then the welding seam should be welded according to the welding process card. After welding, the appearance and internal quality of the weld seam should be inspected to ensure that there are no pores, slag inclusions, cracks, etc. If necessary, the weld seam should be inspected by shooting or exceeding the control line

Installation of heavier valves

When installing heavy valves (DN>100), lifting tools or equipment should be used. The lifting rope should be tied to the flange or bracket of the valve, and should not be tied to the handle type valve stem of the valve to avoid damaging the valve.

What are the general requirements for valve installation?

The general requirements for valve installation, the most suitable installation height, and the direction of valves and valve stems on horizontal pipelines are as follows:

(1) Valves should be located in easily accessible, easy to operate, and maintain locations. Valves on rows of pipelines (such as inlet and outlet pipelines) should be centrally arranged, and consideration should be given to setting up operating platforms and ladders. Valves on parallel pipelines should have their centerlines aligned as much as possible. The clear distance between handwheels should not be less than 10Qmm. In order to reduce the spacing between pipelines, valves can be arranged staggered;

(2) The installation position of frequently operated valves should be easy to operate, and the most suitable installation height is around 1.2m from the operating surface. When the height of the valve handwheel center exceeds 2 meters above the operating surface, a platform should be set up for centrally arranged valve groups or frequently operated individual valves and safety valves. Appropriate measures should also be taken for infrequently operated individual valves (such as sprockets, extension rods, movable platforms, and movable ladders). The chain of the sprocket should not obstruct passage. Valves on pipelines and equipment containing hazardous media must not be installed within the height range of a person's head to avoid injury to their head or direct injury to their face due to valve leakage;

(3) Valves used for partitioning equipment should be directly connected to or close to the equipment pipe opening. The valve on the pipeline connected to equipment with extremely hazardous and highly hazardous toxic media should be directly connected to the equipment outlet, and the valve should not be operated by chain wheels;

(4) Accident handling valves such as fire water valves and fire steam valves should be arranged in a dispersed manner, taking into account safe operation during accidents. These types of valves should be arranged behind the control room. The area behind the safety wall, outside the factory building, or at a certain safe distance from the accident site; In order for operators to operate safely in the event of a fire accident;

5) Unless there are special requirements for the process, valves on the bottom pipelines of equipment such as towers, reactors, and vertical vessels shall not be arranged inside the skirt;

(6) The shut-off valve of the horizontal branch pipe led out from the main pipe should be located on the horizontal pipe section near the root;

(7) Lift check valves should be installed on horizontal pipelines, while vertical lift check valves should be installed on vertical pipelines where the medium flows from bottom to top inside the pipeline. Swing check valves should be installed first on horizontal pipelines, and can also be installed on vertical pipelines where the medium flows from bottom to top inside the pipeline; The bottom valve should be installed at the installation height of the centrifugal pump suction, and a butterfly check valve can be selected; When the diameter of the pump outlet is different from that of the connected pipeline, a reducing check valve can be used;

(8) The center distance of the handwheel of valves arranged around the operating platform should not be greater than 450mm from the edge of the operating platform. When the valve stem and handwheel extend above the platform and the height is less than 2m, they should not affect the operation and passage of operators;

(9) Valves for underground pipelines should be installed in pipe trenches or valve wells, and if necessary, valve extension rods should be installed. Fire water valve wells should have clear markings;

(10) The direction of the valve stem on a horizontal pipeline can be determined in the following order: vertically upward; Level; Tilt upwards at 45 °; Tilt downwards at 45 °; Do not vertically downward;

(11) A rising stem valve with a horizontally installed valve stem must not affect passage when the valve is opened.

Attention should be paid to the installation of check valves

(1) The installation position, height, and inlet/outlet direction must meet the design requirements, and the direction of medium flow should be consistent with the arrow direction marked on the valve body. The connection should be firm and tight.

(2) Before installing the valve, a visual inspection must be conducted, and the valve nameplate should comply with the current national standard "General Valve Marking" GB 12220. For valves with a working pressure greater than 1.0 MPa and a shut-off function on the main pipeline, strength and tightness tests should be conducted before installation, and they can only be used after passing the tests. During the strength test, the test pressure shall be 1.5 times the nominal pressure, and the duration shall not be less than 5 minutes. The valve shell and packing shall be qualified if there is no leakage. During the tightness test, the test pressure is 1.1 times the nominal pressure; The duration of the experiment meets the requirements of GB 50243.

(3) Do not let the check valve bear weight in the pipeline. Large check valves (AETV One way valves) should be independently supported to prevent them from being affected by the pressure generated by the piping system.

Technical requirements for valve installation

1. Directionality. The valve body of a general valve is marked with an arrow pointing in the direction of forward gas flow. Special attention must be paid not to install it backwards. Because various valves require one-way gas flow, such as safety valves, pressure reducing valves, check valves, throttle valves, etc. For globe valves, in order to facilitate opening and maintenance, gas is also required to pass through the valve seat from bottom to top. However, when installing gate valves and plugs, there is no restriction on the flow direction.

2. Installation location. Long term operation and maintenance of valves should be considered, making it as convenient as possible for operation and maintenance, while also paying attention to the aesthetic appearance during assembly.

The direction of the valve handle can be vertically upward, tilted to a certain angle, or placed horizontally, but the handwheel must not be downward to avoid upside down operation; The handwheel of the landing valve should be chest high for easy opening and closing; Bright stem gate valves should not be used underground to prevent corrosion of the valve stem.

Some valves have special installation requirements, such as pressure reducing valves requiring vertical installation on horizontal pipelines without tilting, and lift check valves requiring vertical valve discs; The swing check valve requires the pin shaft to be horizontal. In short, the installation position of the valve should be determined based on its principle, otherwise the valve cannot work effectively or even fail to function.

3. Installation of the plug valve. Check the specifications and models, identify if there is any damage, remove the cover of the threaded mouth and excess grease and debris inside the thread, and inspect the sealing performance of the plug. Proper force must be applied during the installation of gas plugs, and different specifications of pipe clamps or wrenches should be selected according to the size of the plug for installation.

4. When installing threaded valves, the valve company should ensure that the threads are intact and undamaged; Use a timely wrench instead of pipe pliers to avoid damaging the appearance of the valve body.

5. The installation of flange valves must ensure that the two flange sections are parallel to each other and on the same axis. When tightening bolts, they should be cross crossed to ensure even force distribution on the valve end face.

6. Valves connected by flanges and threads should be installed in the closed state. When welding valves to pipelines, argon welding should be used at the bottom of the weld seam to ensure internal cleanliness. During welding, the valve should not be closed to prevent thermal deformation.

7. In general, valves are directly connected to corrugated expansion joints, so the pipes on both sides should be cut off according to the size of the valve and corrugated expansion joint, as well as the flange and gasket, leaving installation space.

8. When lifting valves, ropes should not be tied to the first wheel or valve stem to prevent damage. They should be lifted and placed gently without collision. When placed on the support pier, stabilize and level it according to the required elevation. There must be sturdy supports or brackets under the valve to support it, and it is not allowed for the valve to be suspended and generate stress.