Wrong valve installation method.
For example, the water (steam) flow direction of stop valve or check valve is opposite to the sign, the valve stem is installed downward, the check valve installed horizontally is installed vertically, the handle of rising stem gate valve or butterfly valve has no space for opening and closing, and the valve stem of concealed valve does not face the inspection valve.
Consequence: valve failure, switch maintenance difficulties, stem down often cause water leakage.
Measures: install in strict accordance with the valve installation instructions. The rising stem gate valve shall have enough stem extension opening height. The handle rotation space shall be fully considered for the butterfly valve. The stem of various valves shall not be lower than the horizontal position or downward. The concealed valve shall not only be provided with an inspection valve meeting the opening and closing requirements of the valve, but also the valve stem shall face the inspection valve.
The specification and model of the installed valve do not meet the design requirements.
For example, the nominal pressure of the valve is less than the system test pressure; when the pipe diameter of the water supply branch pipe is less than or equal to 50 mm, the gate valve is used; the stop valve is used for the dry and vertical pipes of hot water heating; the butterfly valve is used for the water suction pipe of the fire pump.
Consequence: affect the normal opening and closing of the valve and adjust the resistance, pressure and other functions. Even cause system operation, valve damage forced to repair.
Measures: be familiar with the application scope of various valves, and select the specifications and models of valves according to the design requirements. The nominal pressure of the valve shall meet the requirements of system test pressure. According to the requirements of construction specification: stop valve shall be used when the diameter of water supply branch pipe is less than or equal to 50mm; gate valve shall be used when the diameter is greater than 50mm. Gate valve shall be used for hot water heating dry and vertical control valve, and butterfly valve shall not be used for fire pump suction pipe.
Before the installation of the valve, necessary quality inspection is not carried out as required.
Consequence: during the operation of the system, the valve switch is not flexible, the closing is not strict and the phenomenon of water (steam) leakage occurs, causing rework and repair, even affecting the normal water supply (steam).
Measures: pressure strength and tightness test shall be conducted before valve installation. 10% of each batch (of the same brand, specification and model) shall be selected for the test, and no less than one.
For the closed-circuit valves installed on the main pipe to cut off, strength and tightness tests shall be conducted one by one. The valve strength and tightness test pressure shall comply with the provisions of code for acceptance of construction quality of building water supply and drainage and heating engineering (GB 50242-2002).
The main materials, equipment and products used in the construction are lack of technical quality identification documents or product certificates that meet the current standards issued by the state or the Ministry.
Consequence: the project quality is unqualified, there are potential accidents, and it cannot be delivered and used on time, so it must be reworked and repaired; the construction period is delayed, and the input of labor and materials is increased.
Measures: the main materials, equipment and products used in the water supply and drainage and heating and sanitation engineering shall be provided with technical quality appraisal documents or product certificates that meet the current standards issued by the state or the Ministry; the product name, model, specification, national quality standard code, delivery date, manufacturer’s name and location, delivery product inspection certificate or code shall be indicated.
Consequence: the check valve, throttle valve, pressure reducing valve, check valve and other valves are directional. If they are installed reversely, the throttle valve will affect the service effect and life; the pressure reducing valve will not work at all, and the check valve will even cause danger.
Measures: for general valves, there is a direction mark on the valve body; if not, it should be correctly identified according to the working principle of the valve. The valve cavity of the stop valve is not symmetrical. The fluid should be allowed to pass through the valve port from bottom to top, so that the fluid resistance is small (determined by the shape), the opening is labor-saving (due to the upward pressure of the medium), and the medium is not pressurized after the closing, which is convenient for maintenance. This is the reason why the stop valve can not be reversed.
Do not install the gate valve upside down (i.e. the hand wheel is downward), otherwise, the medium will remain in the valve cover space for a long time, which is easy to corrode the valve stem, and is forbidden by some process requirements. At the same time, it is inconvenient to change the packing.
Open stem gate valve shall not be installed underground, otherwise exposed stem will be corroded due to humidity.
When installing the lift check valve, make sure that the valve disc is vertical, so that the lift is flexible.
The swing check valve shall be installed with its pin shaft horizontal so that it can swing flexibly.
The pressure relief valve shall be installed vertically on the horizontal pipeline and shall not be inclined in all directions.
Post time: Nov-27-2019