Valves Commonly Used in Sewage and Wastewater Treatment Facilities

Valves play a crucial role in controlling fluid flow and isolating media in wastewater treatment facilities. A wide variety of valve types are utilized in water treatment projects, with most of them being standardized products. Chemical valves are employed when corrosion resistance is required, while customized designs are used for special requirements.

Wastewater treatment plants utilize various types of valves based on the type of media and their function. These include sewage valves, sludge valves, clean water valves, gas valves, and oil valves. In terms of function, valves can be classified as gate valves, flow control valves, check valves, safety valves, among others. Structurally, valves can be gate valves, butterfly valves, ball valves, plug valves, angle valves, etc. The fundamental parameters of valves include the flow diameter and the working pressure of the medium.

Here are several commonly used valves in wastewater treatment:

Gate Valve

The flowing medium of gate valves can be clean water, sewage, sludge, floating scum, oil, or gas. Its flow diameter is generally 501000mm, and the maximum working pressure can be up to 24MPa. The characteristic of gate valves is that when the valve is fully open, the passage is completely unobstructed, so the resistance to fluid flow through the valve is minimal, and entanglement will not occur. Therefore, gate valves are suitable for use in pipelines with a large amount of impurities such as sewage and sludge. However, gate valves have disadvantages such as long sealing surfaces, easy leakage, and large volume.

Gate valves are composed of a valve body, a gate (also called a gate), sealing components, and an opening and closing device. The gate is opened and closed by reciprocating linear motion. To prevent leakage, both surfaces and both sides of the gate must form a good seal with the valve body. Therefore, a narrow and long gap between the valve body and the gate must be lined with bronze, rubber, or serrations. Gate valves have visible and hidden stem opening and closing devices, manual, electric, or hydraulic.

Butterfly Valve

The butterfly valve is the most widely used valve in wastewater treatment. Its flowing medium includes sewage, clean water, activated sludge, low-pressure gas for aeration, etc. Its maximum flow diameter can exceed 2 meters.

Butterfly valves are composed of a valve body, a lining, a butterfly plate, and an opening and closing mechanism. The valve body is generally made of cast iron, and special materials such as stainless steel and plastic are also used. It is mostly connected to the pipeline with flanges. The main function of the lining is to seal between the valve body and the butterfly plate to avoid contact between the medium and the cast iron valve body and flange sealing. The lining is mostly made of rubber or nylon. Stainless steel butterfly valves have no lining. The butterfly plate moves by rotation, and the maximum rotation angle is 90°. The material of the butterfly plate depends on the medium. Some are made of steel with anticorrosive layers or coatings, and some are made of stainless steel or aluminum alloy. The central axis of the butterfly plate is fixed on the upper and lower sliding bearings of the valve body. The opening and closing mechanism of butterfly valves includes manual and electric types. Small butterfly valves can be operated directly by hand, while larger ones need to be rotated with the help of a worm gear turbine for speed reduction and torque increase. For butterfly valves with a diameter greater than 500mm, in addition to using worm gear reduction, gear reduction and helical reduction must be added to make the butterfly plate rotate.

The advantages of butterfly valves are their small size and good sealing performance compared to valves of the same diameter. The disadvantage is that after the valve is opened, the butterfly plate still lies in the center of the flow passage, which will cause resistance to the flow of the medium, and debris in the medium will entangle on the butterfly plate. Therefore, butterfly valves should be avoided in pipelines with floating scum or pipelines with a lot of floating scum in the medium. In addition, when the butterfly valve is closed, if there is a lot of sediment near the butterfly plate, the sediment will hinder the butterfly plate from opening again.

Ball Valve

The characteristic of the ball valve is that the valve core is spherical, with a through hole of the same diameter in the middle, and the opening and closing of the valve are the same as the butterfly valve, which is the rotation of the valve core. When the axial position of the through hole is parallel to the direction of the medium flow, the valve is fully open; when the position of the through hole is perpendicular to the direction of the medium flow, the valve is fully closed. Therefore, there are no obstacles in the pipeline where the medium flows, and even if there is sedimentation when closed, it will not hinder reopening. The sealing performance of the ball valve is good, the action is flexible, and it is suitable for a wide range of media. Some ball valves can withstand pressures of up to 20MPa. In sewage treatment plants, ball valves are often used in small and medium-sized pipelines with a large number of impurities, such as sludge and float pipelines. In addition, due to its good sealing performance and high pressure resistance, ball valves are also commonly used in biogas pipelines in sludge digestion treatment systems. The opening and closing of ball valves are rotary, and the form of the opening and closing device is similar to that of butterfly valves. The disadvantage is that compared with the aforementioned two types of valves, ball valves with the same diameter have much larger size and mass, and higher cost. For this reason, ball valves with a diameter greater than 400mm are generally rare.

Check Valve

In sewage treatment plants, in water pump pits and blower rooms, often one or more water pumps or blowers need to work in parallel to meet the required inflow or airflow. When one of them stops working due to some reasons, the pressurized water or air in the pipeline will flow back into the water pump or blower from the outlet or air outlet of the pump or blower; when all the blowers stop running, the water in the aeration tank will flow into the pipeline or even the blower room due to the pressure at the bottom of the tank. To prevent the above situations, a check valve should be installed on the outlet of each water pump or blower, to prevent backflow.

Check valves, also known as check valves or one-way valves, are composed of a valve body and a flap valve with a spring. Its working principle is simple. When the medium flows forward, the flap valve opens completely under the impact of the medium, and the pipeline is unobstructed; when the medium flows backward, the flap valve closes under the reverse pressure of the medium, preventing the backflow from continuing, thereby ensuring the normal operation of the entire pipeline and protecting the water pump and blower. There are many types and specifications of check valves. According to different media, different flow rates or pressures, different pipe diameters, and different times required to block backflow, different check valves are used. In addition to lift check valves, there are swing check valves, float check valves, and clamp check valves, etc.

Principles and Requirements for Valve Installation in Sewage Treatment

Valve Placement Principles

Valves should be set according to the types and quantities shown on the piping and instrumentation diagram (PID). When the PID has specific requests for the equipment orientation of certain valves, it should be set according to the technical requests.
Valves should be placed in places that are easy to access, operate, and repair. Valves on rows of pipelines should be centrally placed, and consideration should be given to setting up operation channels or ladders.

When the pipelines entering and exiting the equipment corridors are connected to the main pipelines of the entire plant, shut-off valves must be installed. The equipment orientation of the valves should be centrally placed on one side of the equipment area, and necessary operation channels or maintenance channels should be set up.
Valves that need to be operated, repaired, and replaced frequently should be located close to the ground, channels, or ladders. Pneumatic and electric valves should also be placed in convenient locations.
Valves that do not need to be operated frequently (only used during start-up and shutdown) should also be placed where they can be operated on the ground when it is not possible to operate from above ground.
The base of the valve handwheel should be 7501500mm from the operating surface, with the most suitable height being 1200mm. For valves that do not need to be operated frequently, the equipment height can reach 15001800mm. When the equipment height cannot be lowered and frequent operation is required, operation channels or steps should be provided. Valves on pipelines and equipment with risk media should not be set within the range of people's head heights.
When the base of the valve handwheel is more than 1800mm from the operating surface, chain operation is recommended. The distance of the chain from the ground should be about 800mm, and a chain hook should be provided to hang the chain's lower end on the nearby wall or pillar to avoid affecting passage.
For valves set in pipeline trenches, when the trench cover can be opened for operation, the valve handwheel should not be less than 300mm below the trench cover. When it is lower than 300mm, a valve extension rod should be installed to ensure that the handwheel is within 100mm below the trench cover.
For valves set in pipeline trenches that need to be operated from above ground, or valves located under the upper floor (channel) of equipment, valve extension rods can be installed to extend to the trench cover, floor, or channel for operation, with the handwheel of the extension rod being 1200mm from the operating surface. Valves with a nominal diameter of less than or equal to DN40 and threaded connections should not be operated using chains or extension rods to avoid damaging the valves. In general, chains or extension rods should be used as little as possible to operate valves.
The distance between the handwheel of valves placed around channels and the edge of the channel should not exceed 450mm. When the valve stem and handwheel extend into the channel above and the height is less than 2000mm, they should not affect the operation and passage of personnel, to avoid causing personal injury.

Setting Requirements for Large Valves

Large valves should be operated with gear transmission mechanisms, and consideration should be given to the space required for the transmission mechanism. Typically, valves larger than the following sizes should be considered for the use of valves with gear transmission mechanisms.
Support brackets should be installed on one or both sides of large valves. The brackets should not be placed on short pipes that need to be disassembled during maintenance, and consideration should be given to not affecting the support of the pipeline when removing the valve. The distance between the bracket and the valve body flange should generally be greater than 300mm.
The equipment orientation of large valves should have places for using cranes, or consideration should be given to setting up lifting columns or beams.

Setting Requirements for Valves on Horizontal Pipelines

Except for special technical requests, the handwheels of valves on horizontal pipelines should not face downwards, especially on pipelines carrying hazardous media, where valve handwheels facing downwards are strictly prohibited. The orientation of the valve handwheel is determined in the following order: straight up; horizontal; left or right inclined 45° from straight up; left or right inclined 45° from straight down; not straight down.
For straight stem valves on horizontal equipment, when the valve is fully open, the stem should not obstruct passage, especially when the stem is located at the head or knee of the operator.

Other Requirements for Valve Installation

Valves installed in parallel on pipelines should have their base lines aligned as much as possible. When valves are placed adjacent to each other, the net distance between handwheels should not be less than 100mm; valves can also be staggered to reduce the distance between pipelines.
For valves on pipelines with a nominal diameter of less than DN80 and a pressure rating of less than PN1.0MPa, special tools should be used for operation to avoid deformation or damage to the valve due to excessive force during operation.
The inner and outer surfaces of valve body flanges should be processed to be smooth, and a reasonable gap should be left between the valve body flanges and the equipment flanges to avoid deformation or damage to the flange surface and gasket.
All valve components and accessories should be complete and of the same type and specification as shown in the design drawings and technical documentation. Before installation, the valve body, valve flap, and valve stem should be checked for the necessary assembly and function tests to ensure no quality defects before installation.

These principles and requirements for the installation of valves in sewage treatment plants ensure the safe, reliable, and efficient operation of valves and pipelines in the entire plant, and provide convenience for equipment operation, maintenance, and replacement, thereby effectively ensuring the long-term stable operation of the sewage treatment plant.

Management of Valve Use in Water Treatment

Accidents caused by poor manufacturing quality, inadequate management, and misuse are not uncommon. Some significant and malignant accidents worldwide have been attributed to valve failures. Therefore, strengthening the management of valves is imperative.

1. Technical Documentation Management

Valve technical documentation includes national standards, relevant standards, valve factory instructions, quality certificates, installation construction drawings, maintenance and repair records, daily management cards, and valve change records. Complete and comprehensive valve technical documentation plays a crucial role in critical moments, enabling informed decision-making during routine maintenance and timely replacement of aging valves.

2. Quality Management

This encompasses valve quality assurance systems, total quality management, pressure testing and acceptance systems, quality control points, personal responsibility systems, and handover records.

3. Valve Maintenance Management

This involves repair and maintenance items, content, frequency, performance parameters, acceptance criteria, maintenance plans, completion status, and maintenance records.

4. Usage Record Management

This includes valve model specifications, working pressure, working temperature, medium and flow direction, factory serial number, manufacturer, equipment pipeline name code, major repair records, and valve component replacement records.

5. Valve Well Design and Management

Valves installed in buried pipelines must have valve wells constructed to facilitate daily maintenance and management. The diameter of valve wells must strictly adhere to prescribed dimensions; otherwise, it will significantly affect daily valve operations. Valve wells should preferably be located along roadsides or green belts for easy maintenance. The size of manhole covers should be standardized according to national specifications; oversized or undersized covers can trigger safety accidents, an issue valve managers should be mindful of. Determining the clear space dimensions inside valve wells should facilitate valve maintenance personnel in replacing valve components without damaging the well structure. Valve well management includes ensuring intact manhole covers and proper connection to the road surface, accurate positioning of valve operation holes, absence of debris and sewage inside the well, and taking ventilation measures before maintenance work due to the potential for oxygen deficiency in confined spaces. Valve wells should be regularly inspected, and buried problems should be promptly addressed, while lost or damaged manhole covers should be promptly replaced.

6. Valve Failure Prevention Management

Enhance early-stage management and establish complete records for valve design, material selection, installation, maintenance, repair, and replacement. Before valves enter the pipeline network, pressure tests should be conducted to assess strength and sealing performance, reducing the possibility of substandard valves entering the network. The material of rubber sealing rings has a significant impact on the service life of valves, requiring all sealing rings to be made of nitrile rubber or ethylene propylene rubber, and recycled rubber should be strictly prohibited. Control torque during switch operations using torque wrenches to prevent valve damage due to improper operation. Raise material and corrosion resistance requirements.

Conclusion

Effective valve selection, installation, and management are critical for the smooth operation of wastewater treatment facilities. Gate valves, butterfly valves, ball valves, and check valves are among the commonly employed types, each offering unique advantages and considerations. By adhering to proper installation principles and maintenance protocols, operators can ensure the reliable performance of valves, contributing to the efficient and safe operation of wastewater treatment processes.

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