Taboo 1

The valve is installed incorrectly.

For example, the water (steam) flow direction of the stop valve or check valve is opposite to the sign, and the valve stem is installed downward. The horizontally installed check valve is installed vertically. The handle of the rising stem gate valve or butterfly valve has no opening and closing space. The stem of the concealed valve is installed. Not toward the inspection door.

Consequences: The valve fails, the switch is difficult to repair, and the valve stem points downward, often causing water leakage.

Measures: Install strictly in accordance with the valve installation instructions. For rising-stem gate valves, leave sufficient valve stem extension opening height. For butterfly valves, fully consider the handle rotation space. Various valve stems cannot be lower than the horizontal position, let alone downward. Concealed valves must not only be equipped with an inspection door that meets the valve opening and closing requirements, but also the valve stem should be facing the inspection door.

Taboo 2

The specifications and models of the installed valves do not meet the design requirements.

For example, the nominal pressure of the valve is less than the system test pressure; gate valves are used when the pipe diameter of the water supply branch pipe is less than or equal to 50mm; stop valves are used for dry and standpipe pipes of hot water heating; butterfly valves are used for fire water pump suction pipes.

Consequences: Affecting the normal opening and closing of the valve and regulating resistance, pressure and other functions. It may even cause the valve to be damaged and have to be repaired while the system is running.

Measures: Be familiar with the application range of various types of valves, and select valve specifications and models according to design requirements. The nominal pressure of the valve must meet the system test pressure requirements. According to the requirements of construction specifications: when the diameter of the water supply branch pipe is less than or equal to 50mm, a stop valve should be used; when the pipe diameter is greater than 50mm, a gate valve should be used. Gate valves should be used for hot water heating dry and vertical control valves, and butterfly valves should not be used for fire water pump suction pipes.

Taboo 3

Failure to carry out necessary quality inspections as required before valve installation.

Consequences: During system operation, the valve switches are inflexible, closed tightly and water (steam) leaks occur, causing rework and repair, and even affecting the normal water supply (steam).

Measures: Before installing the valve, pressure strength and tightness tests should be carried out. The test should randomly check 10% of each batch (same brand, same specification, same model), and no less than one. For closed-circuit valves installed on main pipes with a cutting function, strength and tightness tests should be conducted one by one. The valve strength and tightness test pressure should comply with the “Construction Quality Acceptance Code for Building Water Supply, Drainage and Heating Projects” (GB 50242-2002).

Taboo 4

The main materials, equipment and products used in construction lack technical quality appraisal documents or product certificates that comply with current national or ministerial standards.

Consequences: The quality of the project is unqualified, there are hidden dangers of accidents, it cannot be delivered on time, and must be reworked and repaired; resulting in delays in the construction period and increased investment in labor and materials.

Measures: The main materials, equipment and products used in water supply, drainage and heating and sanitation projects should have technical quality appraisal documents or product certificates that comply with current standards issued by the state or the ministry; their product names, models, specifications, and national quality standards should be marked. Code number, date of manufacture, manufacturer’s name and location, factory product inspection certificate or code number.

Taboo 5

Valve flip-up

Consequences: Check valves, throttle valves, pressure reducing valves, check valves and other valves are all directional. If installed upside down, the throttle valve will affect the use effect and life; the pressure reducing valve will not work at all, and the check valve will not work at all. It can even be dangerous.

Measures: Generally, valves have direction marks on the valve body; if not, they should be correctly identified based on the working principle of the valve. The valve cavity of the stop valve is asymmetrical from left to right, and the fluid must pass through the valve port from bottom to top. In this way, the fluid resistance is small (determined by the shape), and it is labor-saving to open (because the medium pressure is upward). After closing, the medium does not press the packing, which is convenient for maintenance. . This is why the stop valve cannot be installed reversely. Do not install the gate valve upside down (that is, with the hand wheel facing downwards), otherwise the medium will remain in the valve cover space for a long time, which will easily corrode the valve stem, and is contraindicated by certain process requirements. It is extremely inconvenient to replace the packing at the same time. Do not install rising stem gate valves underground, otherwise the exposed stem will be corroded by moisture. When installing the lift check valve, ensure that its valve disc is vertical so that it can lift flexibly. When installing the swing check valve, ensure that its pin is level so that it can swing flexibly. The pressure reducing valve should be installed upright on a horizontal pipe and should not be tilted in any direction.

Taboo 6

Manual valve opens and closes with excessive force

Consequences: The valve may be damaged at least, or a safety accident may occur at worst.

Measures: The manual valve, its handwheel or handle, is designed according to ordinary manpower, taking into account the strength of the sealing surface and the necessary closing force. Therefore, long levers or long wrenches cannot be used to move the board. Some people are accustomed to using wrenches, so they should be careful not to use too much force, otherwise it is easy to damage the sealing surface or break the hand wheel or handle. To open and close the valve, the force should be steady and without impact. Some components of high-pressure valves that impact opening and closing have considered that this impact force cannot be equal to that of ordinary valves. For steam valves, they should be preheated and condensed water should be removed before opening. When opening, they should be opened as slowly as possible to avoid water hammer. When the valve is fully open, the handwheel should be turned slightly to make the threads tight to avoid loosening and damage. For rising stem valves, remember the valve stem positions when fully open and fully closed to avoid hitting the top dead center when fully open. And it is convenient to check whether it is normal when fully closed. If the valve stem falls off, or large debris is embedded between the valve core seals, the valve stem position will change when fully closed. When the pipeline is first used, there is a lot of dirt inside. You can open the valve slightly, use the high-speed flow of the medium to wash away it, and then close it gently (do not close quickly or slam it to prevent residual impurities from pinching the sealing surface). Turn it on again, repeat this many times, rinse away the dirt, and then return to normal work. For normally open valves, there may be dirt stuck to the sealing surface. When closing, use the above method to flush it clean, and then officially close it tightly. If the handwheel or handle is damaged or lost, it should be replaced immediately. Do not use a swing wrench to replace it, so as to avoid damage to the four sides of the valve stem, failure to open and close properly, and even an accident in production. Some media will cool down after the valve is closed, causing the valve parts to shrink. The operator should close it again at the appropriate time to leave no slits on the sealing surface. Otherwise, the medium will flow through the slits at high speed and easily erode the sealing surface. . During operation, if you find that the operation is too strenuous, you should analyze the reasons. If the packing is too tight, loosen it appropriately. If the valve stem is skewed, notify personnel to repair it. When some valves are in the closed state, the closing parts are heated and expand, making it difficult to open; if it must be opened at this time, loosen the valve cover thread half a turn to one turn to eliminate the stress on the valve stem, and then turn the hand wheel.

Taboo 7

Improper installation of valves for high temperature environments

Consequences: causing leakage accidents

Measures: High-temperature valves above 200°C are at normal temperature when installed, but after normal use, the temperature rises, the bolts expand due to heat, and the gaps increase, so they must be tightened again, which is called “heat tightening”. Operators should pay attention to this task , otherwise leakage may easily occur.

Taboo 8

Failure to drain water in time in cold weather

Measures: When the weather is cold and the water valve is closed for a long time, the water accumulated behind the valve should be removed. After the steam valve stops steam, the condensed water must also be removed. There is a plug at the bottom of the valve, which can be opened to drain water.

Taboo 9

Non-metallic valve, opening and closing force is too large

Measures: Some non-metallic valves are hard and brittle, and some have low strength. When operating, the opening and closing force should not be too large, especially not with force. Also pay attention to avoid collision with objects.

Taboo 10

The new valve packing is too tight

Measures: When using a new valve, do not press the packing too tightly to avoid leakage, so as to avoid excessive pressure on the valve stem, accelerated wear, and difficulty in opening and closing. The quality of valve installation directly affects its use, so careful attention must be paid to the direction and position of the valve, valve construction operations, valve protection facilities, bypass and instrumentation, and valve packing replacement.