Inspection before valve installation

① Carefully check whether the valve model and specification meet the requirements of the drawing.

② Check whether the valve rod and disc can be opened flexibly and whether they are stuck and skewed.

③ Check whether the valve is damaged and whether the thread of the threaded valve is correct and complete.

④ Check whether the combination of valve seat and valve body is firm, the connection between valve disc and valve seat, bonnet and valve body, and the connection between valve stem and valve disc.

⑤ Check whether the valve padding, packing and fasteners (bolts) are suitable for the requirements of the nature of the working medium.

⑥ The old or long-standing pressure reducing valve should be disassembled, and the dust, sand and other debris must be cleaned with water.

⑦ Clear the port cover, check the sealing degree, and the valve disc must be closed tightly.

Pressure test of valve

Strength test and tightness test shall be carried out for low pressure, medium pressure and high pressure valves, and spectral analysis shall be carried out for alloy steel valves one by one to recheck the material.

1. Strength test of valve

The strength test of the valve is to check the leakage of the outer surface of the valve when the valve is open. For valves with PN ≤ 32Mpa, the test pressure is 1.5 times the nominal pressure, the test time is not less than 5min, and it is qualified if there is no leakage at the shell and packing gland.

2. Tightness test of valve

When the valve is fully closed, check whether there is leakage on the sealing surface of the valve. The test pressure, except for butterfly valve, check valve, bottom valve and throttle valve, should generally be carried out at the nominal pressure. When the working pressure can be determined, the test can also be carried out at 1.25 times the working pressure, and the valve disc sealing surface is qualified if there is no leakage.

General provisions for valve installation

1. The installation position of the valve shall not hinder the operation, disassembly and maintenance of the equipment, pipeline and valve body, and at the same time, the beauty of the assembly appearance shall be considered.

2. For the valve on the horizontal pipeline, the valve stem shall be installed upward or inclined at a certain angle, and the handwheel shall not be installed downward. The valve, valve rod and hand wheel on the high-altitude pipeline can be installed horizontally, and the valve can be opened and closed remotely with the chain at the lower vertical position.

3. The arrangement is symmetrical, neat and beautiful; For the valve on the riser, if the process permits, the valve handwheel is most suitable for operation at chest height, generally 1.0-1.2m from the ground, and the valve stem must be installed along the direction of the operator.

4. For the valves on the parallel riser, the elevation of the center line should be the same, and the clear distance between the hand wheels should not be less than 100mm; Valves on side-by-side horizontal pipelines shall be installed staggered to reduce the distance between pipelines.

5. When installing heavy valves on water pumps, heat exchangers and other equipment, valve supports should be set; When the valve is operated frequently and installed more than 1.8m away from the operation surface, a fixed operation platform shall be set.

6. If there is an arrow mark on the valve body, the direction of the arrow is the flow direction of the medium. When installing the valve, pay attention to make the arrow point to the same direction as the medium flow in the pipeline.

7. When installing flange valves, ensure that the end faces of the two flanges are parallel and concentric with each other, and double gaskets are not allowed.

8. When installing threaded valves, in order to facilitate disassembly, a threaded valve should be equipped with a union. The setting of the union should consider the convenience of maintenance. Usually, the water flows through the valve first and then through the union.

Precautions for valve installation

1. The valve body material of the valve is mostly made of cast iron, which is brittle, so it must not be impacted by heavy objects.

2. When handling the valve, it is not allowed to throw it casually; When lifting and hoisting the valve, the rope should be tied to the valve body, and it is strictly prohibited to tie it to the hand wheel, valve rod and flange bolt hole.

3. The valve should be installed in the most convenient place for operation, maintenance and overhaul, and it is strictly prohibited to be buried underground. Inspection chambers shall be set for valves on pipes directly buried and in trenches to facilitate the opening, closing and adjustment of valves.

4. Ensure that the thread is intact, and wrap hemp, lead oil or PTFE raw material tape on the thread. When screwing, use a wrench to clamp the hexagonal valve body screwed into one end of the pipe.

5. When installing the flange valve, pay attention to tighten the connecting bolts along the diagonal direction, and the force should be even when screwing, so as to prevent the gasket from deviation or cause the deformation and damage of the valve body.

6. The valve shall be kept closed during installation. For threaded valves close to the wall, it is often necessary to remove the valve stem, disc and handwheel before screwing. During disassembly, the hand wheel should be screwed to keep the valve open before disassembly.

Installation of common valves

Installation of gate valve

Gate valve, also known as gate plate valve, is a valve that uses the gate to control the opening and closing of the valve. It can adjust the flow of the pipeline and open and close the pipeline by changing the cross section. Gate valves are mostly used for pipelines with full open or full close operation for fluid media. Generally, the installation of gate valve has no directional requirements, but it cannot be inverted.

Installation of stop valve

Stop valve is a valve that uses valve disc to control opening and closing. Adjust the medium flow or cut off the medium path by changing the gap between the valve disc and the valve seat, that is, changing the size of the channel section. Pay attention to the flow direction of the fluid when installing the stop valve.

The principle that must be observed in the installation of stop valves is that the fluid in the pipeline passes through the valve hole from bottom to top, commonly known as "low in high out", and it is not allowed to install it upside down.

Installation of check valve

Check valve, also known as check valve and one-way valve, is a valve that automatically opens and closes under the action of the pressure difference between the front and back of the valve. Its function is to make the medium flow in only one direction and prevent the medium from flowing backwards. According to their different structures, check valves are lift type, swing type and butterfly wafer type. Lift check valves can be divided into horizontal and vertical ones. When installing the check valve, pay attention to the flow direction of the medium and do not install it upside down.

Installation of pressure reducing valve

The pressure reducing valve is a valve that reduces the inlet pressure to a required outlet pressure through adjustment, and automatically maintains the outlet pressure stable by relying on the energy of the medium itself.

From the perspective of fluid mechanics, the pressure reducing valve is a throttling element whose local resistance can be changed, that is, by changing the throttling area, the flow rate and kinetic energy of the fluid can be changed, resulting in different pressure losses, so as to achieve the purpose of pressure reduction. Then, depending on the regulation of the control and regulation system, the fluctuation of the pressure behind the valve is balanced with the spring force, so that the pressure behind the valve remains constant within a certain error range.

Installation of pressure reducing valve group

1. The pressure reducing valve group installed vertically is generally set at a suitable height from the ground along the wall; The pressure reducing valve group installed horizontally is generally installed on the permanent operating platform.

2. Profile steel shall be loaded into the wall on the outside of two control valves (commonly used for stop valves) to form a bracket, and the bypass pipe is also stuck on the bracket for leveling and alignment.

3. The pressure reducing valve should be installed vertically on the horizontal pipe without tilting. The arrow on the valve body should point to the direction of medium flow and should not be installed reversely.

4. Stop valves and high and low pressure gauges shall be installed on both sides to observe the pressure changes before and after the valve. The diameter of the pipeline behind the pressure reducing valve should be 2 × 3 × 3 × larger than the inlet diameter in front of the valve, and the bypass pipe should be installed for maintenance.

5. The pressure equalizing pipe of the membrane pressure reducing valve should be connected to the low-pressure pipeline. Low pressure pipelines should be equipped with safety valves to ensure the safe operation of the system.

6. When it is used for steam decompression, a drain pipe should be set. For the pipeline system with high purification requirements, a filter shall be set in front of the pressure reducing valve.

7. After the installation of the pressure reducing valve group, the pressure test, flushing and adjustment of the pressure reducing valve and safety valve shall be carried out according to the design requirements, and the adjusted marks shall be made.

8. When flushing the pressure reducing valve, close the inlet valve of the pressure reducer and open the flushing valve for flushing.

Installation of steam trap

The basic function of steam trap is to discharge condensate, air and carbon dioxide gas in the steam system as soon as possible; At the same time, it can automatically prevent the leakage of steam to the greatest extent. There are many kinds of traps, each with different performance.

According to the different working principles of steam traps, they can be divided into the following three types:

Mechanical type: action depends on the change of condensed water level in the steam trap, including:

Floating ball type: the float is a closed hollow sphere.

Open upward float type: the float is a bucket type with an open upward.

Open downward float type: the float is a bucket type with the opening downward.

Thermal static type: it acts depending on the change of liquid temperature, including:

Bimetallic sheet: the sensitive element is bimetallic sheet.

Steam pressure type: the sensitive element is a bellows or ink cartridge, which is filled with volatile liquid.

Thermodynamic type: it acts depending on the change of the thermodynamic properties of the liquid.

Disc type: due to the different flow rates of liquid and gas under the same pressure, the different dynamic and static pressure will drive the disc valve to act.

Pulse type: when condensate with different temperatures passes through the throttle orifice plates connected in series at the two poles, different pressures will be formed between the throttle orifice plates at the two poles to drive the action of the valve disc.

Installation of steam trap

1. Block valves (stop valves) shall be set at the front and rear, and filters shall be set between the drain valve and the front block valve to prevent dirt in the condensate from blocking the drain valve.

2. An inspection pipe should be set between the drain valve and the rear block valve to check whether the drain valve works normally. If the inspection pipe is opened for a large amount of steam, it indicates that the drain valve is broken and needs maintenance.

3. The bypass pipe is set to discharge a large amount of condensate during startup and reduce the drainage load of the drain valve.

4. When the drain valve is used to drain the condensate of the thermal equipment, it should be installed at the lower part of the thermal equipment to make the condensate pipe vertically return to the steam trap to prevent water storage of the thermal equipment.

5. The installation position should be as close to the drainage point as possible. If the distance is too far, air or steam will accumulate in the slender pipe in front of the trap.

6. When the horizontal pipeline of the steam main is too long, the drainage problem should be considered.

Installation of safety valve

Safety valve is a special valve in which the opening and closing parts are normally closed under the action of external forces. When the medium pressure in the equipment or pipeline rises beyond the specified value, the medium pressure in the pipeline or equipment can be prevented from exceeding the specified value by discharging the medium outside the system.

Safety valves are automatic valves, which are mainly used in boilers, pressure vessels and pipelines. The control pressure does not exceed the specified value, which plays an important role in protecting personal safety and equipment operation. Note the safety valve can only be used after pressure test.

1. Before installation, the product must be carefully checked to verify whether there is a certificate of conformity and product instructions, so as to clarify the constant pressure at the time of delivery.

2. The safety valve shall be arranged near the platform as far as possible for inspection and maintenance.

3. The safety valve should be installed vertically, the medium should flow out from bottom to top, and the verticality of the valve rod should be checked.

4. Generally, block valves cannot be set at the front and back of the safety valve to ensure safety and reliability.

5. Safety valve pressure relief: when the medium is liquid, it is generally discharged into the pipeline or closed system; When the medium is gas, it is generally discharged to the outdoor atmosphere;

6. The oil and gas medium can generally be discharged into the atmosphere. The outlet of the safety valve vent pipe should be 3M higher than the highest structure around, but the following situations should be discharged into the closed system to ensure safety.

7. The diameter of the population pipeline shall be at least equal to the inlet diameter of the valve; The diameter of the discharge pipe shall not be less than the outlet diameter of the valve. The discharge pipe shall be led outdoors and installed with elbows, so that the outlet of the pipe faces the safety zone.

8. When the safety valve is installed, when the connection between the safety valve and equipment and pipeline is open-ended welding, its opening diameter should be the same as the nominal diameter of the safety valve.