A wide variety of valves are used in water treatment projects, most of which use definitive products. Chemical valves are used when there are anti-corrosion requirements, and if there are special requirements, they can be designed and manufactured separately.
From the type of media, the valves used in wastewater treatment plants are sewage valves, sludge valves, clear water valves, gas valves, oil valves, etc. From the function, there are globe valves, flow control valves, check valves, safety valves, etc. From the structure, there are gate valves, butterfly valves, ball valves, plug valves, angle valves, etc. The most basic parameters of valves are flow diameter and medium working pressure.
The following introduces several valves commonly used in wastewater treatment.
The flowing medium of the gate valve can be clear water, sewage, sludge, floating slag, and also oil or gas. Its circulation diameter is generally 50~1000mm, and the maximum working pressure can be 2~4MPa.
When the medium is clear water, usually use the soft seal gate valve; circulation medium is sewage, more inclined to use the hard seal gate valve; knife gate valve is generally used in sludge and other slurry types of working conditions.
The gate valve is characterized by a completely obstacle-free channel when the valve is fully open, so the fluid passes through the gate valve with minimum resistance and does not wind up, so it is suitable for use in the pipeline of sewage and sludge containing a large number of impurities. However, there are disadvantages of gate valves such as long sealing surface, ease to leak, and large size.
The gate valve consists of the valve body, gate plate (also called insert), seal, and opening and closing device. The gate opens and closes in a reciprocating flat motion, in order to prevent leakage, the two planes and two sides of the gate must form a good seal with the valve body, so a narrow gap between the valve body and the gate contact should be set with brass, stainless steel, STL… The gate valve opening and the closing device have an open rod and a concealed rod, manual, electric, or hydraulic.
The butterfly valve is the most widely used valve in wastewater treatment, its circulation medium is sewage, clear water, activated sludge, aeration with low-pressure gas, etc… Its maximum circulation diameter can exceed 2m.
A butterfly valve is composed of the valve body, liner, butterfly plate, and opening and closing mechanism. The valve body is generally made of cast iron, ductile iron, and WCB, special ones are also made of stainless steel and plastic PE, PVC, etc. It is connected to the pipeline mostly by the flange & WAFER.
The main role of the liner is to achieve the sealing of the valve body and the butterfly plate, to avoid contact between the medium and the cast iron valve body, and the flange sealing. The liner is mostly made of rubber material or nylon material such as EPDM, PTFE, PPL, NBR, and stainless steel butterfly valve has no amount of liner.
The butterfly plate movement is rotation, and the maximum rotation angle is 90°. The material of the butterfly plate is determined by the medium, either steel material with an anti-corrosion Xu layer or plating layer, or stainless steel or aluminum alloy. The central axis of the butterfly plate is fixed on the two sliding bearings on the top and bottom of the valve body. The opening and closing mechanisms are divided into two types: manual and electric. Small butterfly valves can be turned directly by the handle, while larger ones have to be increased with the help of worm turbine deceleration and force.
The advantage of the butterfly valve is that it is smaller in size compared to its diameter and has good sealing. The disadvantage is that after the butterfly valve is opened, the butterfly plate is still across the center of the flow pipe, which will produce resistance to the flow of the medium, and the debris in the medium will cause winding on the butterfly plate.
Therefore, the butterfly valve should be avoided in the pipeline of floating slag or the pipeline containing more floating slag in the medium. In addition, when the butterfly valve is closed. If there is more mud and sand near the butterfly plate, the mud and sand will prevent the butterfly plate from opening again.
What are the advantages of using ball valves in the wastewater treatment process?
The ball valve is characterized by a spherical spool with a through-hole of the same diameter in the middle, and the valve opens and closes in the same way as the butterfly valve – the rotation of the spool. When the axial position of the through-hole is parallel to the media flow, the valve is fully open; when the position of the through-hole is perpendicular to the direction of media flow, the valve is fully closed.
Therefore, there is no obstacle in the pipeline of media flow, even if there is mud and sand siltation when closing, it will not prevent re-opening. The ball valve has good seals, flexible action, and a wide range of adaptable media, and some ball valves can withstand pressures up to 20MPa.
In sewage treatment plants, ball valves are commonly used in small and medium-sized pipelines containing more debris, such as sludge and floating light pipelines. In addition, using its characteristics of good sealing and high-pressure resistance, ball valves are often used in the biogas pipeline of sludge digestion and treatment system.
The opening and closing of the ball valve are rotating, and the form of the opening and closing device is similar to that of the butterfly valve. The disadvantage is that compared with the two aforementioned valves, the volume and mass of the ball valve with the same diameter are much larger and the cost is higher. For this reason, more than 400mm diameter ball valves are generally not common.
In the pump bottom and blower room of the wastewater treatment plant. Often, we have to work in parallel with a dry pump or blower to meet the required water intake or air supply volume. When one of them stops working due to some factors, the pressure water or air in the pipe network will flow backward into the water bundle or blower from the water outlet or air outlet of that pump or blower.
When all the blowers stop running shield, the water in the aeration pool will flow into the pipe network or even the blower room through the aeration head due to the pressure at the bottom of the pool. To avoid the above situation, a check valve is installed in the small water gate or outlet of each pump or blower to prevent backflow.
A check valve is also called a check valve or one-way valve. It consists of a valve body and a spring-loaded flap door. Its working principle is very simple when the medium is flowing in the positive direction, the flap door in the medium of the impact all open, and the pipeline is unobstructed; when the medium backflow, the flap door in the medium of the reverse pressure to close, in order to prevent the continuation of backflow, thus ensuring the normal operation of the entire pipeline network, the protection of the pump and blower.
There are many varieties and specifications of check valves, people use different check valves according to the different media, different pipeline flow or pressure, different pipeline caliber, and different times required to cut off the backflow, in addition, to lift check valves, there are swing check valves, floating ball check valves, butt check valves, etc.