Summary of Valve Selection in Waterworks


The conventional water production process of the water […]

The conventional water production process of the water plant takes the raw water from the raw water, flocculates and settles in the sedimentation tank, and filters through the filter tank until the outlet pump room outputs the water supply, all of which are inseparable from the use of valves. However, the selection requirements for the valve are very different in different parts. The main difference lies in the diameter of the valve, the type of valve and the control method of the valve.
1 Process valve for raw water intake
The valve of the head raw water is characterized by a large valve diameter and no need for frequent operation. Most of it is only needed once a year or even a few years, and the valve is in a normally open or normally closed state for a long time. Therefore, from the control method, more than 95% of the manual valves are selected, and the valve types are gate valves or butterfly valves. Since the head loss of the gate valve is better than that of the butterfly valve, the head valve gate valve is slightly more than the butterfly valve. The caliber is concentrated in 1200~1600mm, and there are also valves with a caliber of 3000mm on the head inlet pipe.

2 Sedimentation tank valve
The valves of the sedimentation tank are mainly inlet valves, outlet valves and isolation valves. The outlet valve is basically in a normally open state, and the isolation valve is basically in a normally closed state, and is operated once a year, so manual gate valves are used for both types of valves, with specifications ranging from 2200×1800 to 1200×840. The inlet valve of the sedimentation tank bears the important responsibility of water distribution, requiring frequent adjustment, reliable performance, and distributed in front of each sedimentation tank, the distribution is relatively scattered, and all use electric control valves with intelligent control systems. It is a key link that determines the water volume of the sedimentation tank and the balance of the system. It is particularly important for a system where the water production line is dynamically adjusted according to the water output, and PID dynamic tracking adjustment is also required. At this time, for the full stroke time of the valve, The allowable start-stop frequency will have corresponding requirements.

3 Filter valve
The common filter tank is a four-valve filter tank, which is also the most basic configuration of the filter tank. That is to say, no matter which kind of filter tank, there are at least four types of valves: water inlet valve, drain valve, flush valve and clear water valve. Of course, there are also many five-valve, six-valve and even seven-valve filter tanks, and they are also equipped with air flush valves, primary filter valves or more equipped with an inlet valve and so on. From the structure of the valve, the butterfly valve is usually used to distinguish the clear water valve and the flush valve. The main reason is that the clear water valve and the flush valve are installed on the pipeline in the pipe gallery, and the clear water valve needs to be adjusted frequently, and the flush valve will also adjust the flushing intensity. Demand. The water intake and drainage are usually carried out through channels, so the inlet valve and the drain valve basically use gate valves. The diameter of the flush valve of the filter is slightly larger than that of the clear water valve. The flush valve is basically between DN600 and DN800, and the clear water valve is between DN400 and DN600. The size of the inlet valve and drain valve is related to the channel size. From the point of view of control methods, these four types of valves all adopt electric control or pneumatic control. However, the clean water valve must be an adjustable intelligent control mode, which is consistent with the requirements of the sedimentation tank inlet valve. In addition, considering the integrated wiring and modular design method, the filter valve can be selected as a bus-based control mode or a PLC site-based control mode. The advantage of the former is that it saves wiring space, while the advantage of the latter is that it separates the single-cell filter for easy maintenance, management and transplantation.

4 Pump room valve
The valves in the pump room are mainly the inlet valve, outlet valve, maintenance valve and check valve on the pump unit. The first three kinds of valves basically use butterfly valves, and the difference lies in the control method. The inlet valve and the maintenance valve only need manual valves, because one of them is normally open and the other is normally closed, while the outlet valve needs to be opened and closed every time the pump is turned on or off. If you consider the use of the outlet valve to adjust The amount of water makes the pump have different working conditions to meet the demand factors, and the outlet valve also needs to be controlled by a regulating intelligent device. In order to prevent the occurrence of water flow and the occurrence of water hammer, the check valve is usually selected as a silent check valve or a slow-closing check valve with a slight resistance. Sometimes a multi-function valve is used to integrate the water check function.

Valve of water plant dosing system
The characteristics of the water plant dosing system determine that the valve used on it has a small caliber and a small flow rate, but it has high requirements for flow adjustment, high precision and fast adjustment speed. Therefore, flow control valves are usually used. This kind of valve makes the medium flow capacity only Depends on the structure of the valve itself, so that the flow adjustment can be completed at one time. In addition, the medium in the pipeline of the dosing system is ammonium sulfate, sodium hypochlorite and other solutions, which requires the valve to also have the ability to resist corrosion. In addition, the dosing system will also use ball valves as on-off valves, back pressure valves, etc.

Valve selection steps

Determine the process requirements, that is, determine the pressure and flow in the on-site pipeline.
Choose the type of valve according to the diameter of the pipeline and on-site working conditions, combined with the process parameters of the step, choose the valve, and at the same time, decide whether to install an extension pipe according to the installation position of the valve.
The transmission mechanism is selected according to the transmission form. The butterfly valve of the water plant is mostly a multi-turn rotating mechanism, and the gate valve is a straight-stroke transmission mechanism.
To determine the control method, the pneumatic control system is the choice of the cylinder and the supporting transmission mechanism, and the electric control system is the choice of the electric actuator. The selection of the electric actuator is to determine the speed ratio and output torque of the transmission mechanism, the interface type, and the speed and power of the motor according to the full stroke time required by the valve, the torque of the valve and other parameters.
Consider the protection level of the actuator, the communication method, and whether to use other configurations such as thyristor.
With the improvement of the automation level, the requirements for valves in water plants are getting higher and more, but no matter what the change, the conventional selection is roughly within the scope of this article. The main valves are mentioned in this article. Of course, the water plant also uses exhaust valves, solenoid valves, etc., which will not be described in detail here.