Introduction: The siphon drainage pipe system is different from the traditional gravity drainage system. It can promptly remove rainwater and snowwater falling on the roof of the building, avoiding the formation of roof water that threatens the roof, or preventing rainwater from overflowing. Floods, roof leaks and other flood accidents. How is a siphon drainage pipe designed? What is the magic of siphon drainage pipe design? This time Xiaotu will explore the principles of siphon drainage pipe design with everyone, and try to learn the practical steps of designing a siphon drainage pipe.
The difference between siphon drainage system and traditional gravity drainage system
Characteristics of siphon drainage:
1. As long as the calculation requirements are met, the number of rainwater buckets in a single system No limit.
2. The rainwater bucket has a large flow rate, separates air and water, and has fast drainage speed and good effect.
3. The suspension pipe is in a horizontal state and does not require any slope, making construction convenient.
4. The riser pipe diameter is small and the number is small, making it easy to decorate.
5. There are few buried pipes and the workload of ground excavation is small, which effectively shortens the construction period.
Characteristics of traditional gravity drainage:
1. The number of rainwater buckets in a single system is limited.
2. The flow rate of the rainwater bucket is small, the air and water merge, and the drainage effect is poor.
3. The diameter of the risers is large and the number is large, so it is easy to fight during cross construction.
4. There are many buried pipes, the workload of civil construction is heavy, and the trenches are prone to water return.
Design principle of siphon drainage system
When the designed rainfall is reached, all pipes in the real siphon system will show full pipe flow, and the pressure distribution in the pipes is different from that of traditional drainage. There are also many differences in systems. Since the entire height difference between the roof rainwater bucket and the ground drainage well is fully utilized, compared with the gravity drainage system, when the diameters of the siphon drainage pipe and the gravity drainage pipe are equal, the water flow in the siphon pipe is much greater than that of gravity.
The siphon system uses the height of the building, referred to as the water head, to fully consider the hydraulic losses in the pipeline, reduce the diameter of the pipeline as much as possible, and drain rainwater from the roof into the rainwater well. And achieve hydraulic balance by adjusting the structure and length of the vertical tail pipe and horizontal water collecting pipe.
The pressure in pipes is very different from atmospheric pressure. There is no limit to the positive pressure in the pipeline. However, for negative pressure, the evaporation pressure problem, that is, the cavitation problem, must be considered. Therefore, the pressure in the pipeline must be maintained above the evaporation pressure in the area where the system is located.
1. Design of siphon rainwater bucket
The main difference between the gravity drainage rainwater bucket and the siphon system rainwater bucket is that the air baffle is installed in the rainwater bucket. The air baffle is stacked and has no holes. The design of roof bonding components, waterproofing and leaf covers all follows conventional thinking. The diameter combination of the rain bucket body, air baffle and water outlet is a guarantee of stable function under any water flow conditions. This combination is difficult to optimize in theory and must be concluded through a large number of tests and summaries.
2. System pipeline design
Pipeline systems that must meet local national regulations and can withstand positive and negative pressure can be used for siphon system drainage pipes. For example, ABS, PVC, HDPE, PP, copper pipes, steel pipes and cast iron pipes are all successfully used in UV systems. Different plastic pipes have different abilities to withstand negative pressure, and differences in material quality, wall thickness and pipe diameter determine this ability. Pipeline systems are generally selected based on the actual conditions of the project, and factors such as applicability, drainage capacity, durability, rigidity, fire resistance, noise, insulation, cost and installation costs need to be comprehensively considered.
3. Relevant design points:?
(1) Selection of rainwater buckets
Use flat-bottomed metal rainwater buckets to ensure that the rainwater buckets are durable under long-term sunlight. Anti-aging performance and anti-leakage performance. The flat-bottomed rainwater bucket ensures easy and safe construction. Since there are both outer and inner gutters, the patented flat-bottomed rainwater bucket is installed on the concrete roof, which is simple and fast, and can effectively prevent water leakage.
According to the building roof structure form, the siphon rainwater bucket used in this project: The displacement of the siphon rainwater bucket is generally 20?l/s to 40?l/s. When selecting the rainwater bucket, the design displacement It should be designed at 70~80% of the maximum displacement.
Compared with the gravity flow system, the size and number of gutter openings are reduced, which also reduces possible leakage points and saves construction time; siphon systems are mostly series systems, and the roof drains water to the gutter or water collection point through building slopes. When the rainwater buckets are on the same roof partition, the calculation system is based on the same elevation (there are errors in construction, the elevation of each rainwater bucket in the same system on the same roof must be within 50mm, otherwise the system calculation will be invalid and the system will be destroyed). On the other hand, the system calculation At the same time, the water depth in front of the rainwater bucket must also be controlled. If the drainage volume of each water bucket and the water depth in front of the bucket cannot be controlled well, the drainage of the system will be uneven. Only through careful calculation can we ensure that the depth of water accumulation on the roof is reduced and the drainage effect is better. Some systems use high and low access to roof rainwater systems at different elevations to achieve fast and safe drainage. On the premise that the drainage volume of the rainwater bucket is sufficient, precise calculations can be made to ensure the rapid formation of drainage volume and siphon.
(2) Pipe materials
The pipe materials and interfaces selected must be able to meet the needs of both positive and negative pressure. ?The selected pipes can be divided into the following categories:
HDPE pipes: Plastic pipes, low cost, smooth inner wall, good hydraulic conditions, easy construction, and hot melt welding. ?Plastic-coated steel pipe: Steel-plastic composite pipe has a high cost, good rigidity, good fire resistance, smooth inner wall, good hydraulic conditions, long service life, and uses flat clamps or flange connections.
Galvanized steel pipe: Ordinary steel pipe has high cost, good rigidity, good fire resistance, long service life, and is connected by grooved clamps. ?Stainless steel pipe: high-grade drainage steel pipe, the most expensive, with good rigidity, good fire resistance and long service life. It is connected by sub-arc welding or electric welding.
4. Key points for hydraulic calculation of siphon roof drainage system:
(1) The design flow rate of the pipe is not less than 1?m/s.
(2) The total head loss of the drainage pipe should be less than or equal to the geometric height difference between the top surface of the rainwater bucket and the critical point, and the pressure margin ΔPr should be ≤100mbar.
(3)? The siphon roof drainage system has a large negative pressure value at the intersection of the suspension pipe and the main riser. The negative pressure value at this point should have different limit values ??according to different pipe materials. For drainage systems using cast iron and steel pipes, the pipe diameter should be less than 900 mbar; for plastic pipes, the pipe diameter De50-De160 should be less than 800 mbar, and the pipe diameter De200-De300 should be less than 450 mbar.
(4) The pressure difference calculated from different branches at each node of the siphon roof drainage system is not greater than 150?mbar.
(5) The siphon roof drainage system uses inner wall plastic-coated flexible drainage cast iron pipes or steel pipes and high-density polyethylene pipes. The corresponding calculation chart should be used to calculate the head loss along the pipeline.
Practical steps for siphon drainage pipe design
1. First, according to the requirements of the design drawings, determine the roof area where siphon drainage will be used.
2. The area of ??the selected area is measured on the CAD drawing, that is, the roof design catchment area, F.
3. In the rainstorm intensity and rainwater flow calculation software, find out the rainstorm intensity value q(l/s) for a 5-minute rainfall duration based on the specified design return period at the location of the project. ?10000m?)
4. According to the formula, the roof rainwater design flow rate is: Q=k?ΦqFk<1,?Φ>1? Determine which formula to apply by communicating with the staff of the local design institute calculate. Generally, we use the formula Q=qF for calculation. In order to change the unit to l/s, we change the formula to Q=qF/10000? The resulting roof rainwater design flow Q (unit: l/s)
5.?a. According to the roof rainwater The design flow and the given rated flow parameter value of the rainwater bucket determine the number of rainwater buckets. Generally, the calculated sharing value of rainwater buckets should not exceed 20l/s. If it exceeds too much, more buckets should be added.
b. Based on the determined number of rainwater buckets, find the location of the gutter in the CAD drawing, measure the length of the gutter, and then calculate the distance between the rainwater buckets. Generally, between 2 rainwater buckets The distance between them should not be greater than 20m, and then determine the specific position of the rainwater bucket in the drawing.
6. Technical regulations for siphonic roof rainwater drainage system:
(1) For large roofs with a water catchment area greater than 5000 m2, it is recommended to set up no less than 2 independent groups siphon roof rainwater drainage system.
(2) The height difference from the top surface of the rainwater bucket to the transition section should be greater than 3m when the riser diameter is not greater than DN75; when the riser diameter is not less than DN90, it should be greater than 5m;
(3)? The design flow rate of the suspension pipe should not be less than 1.0m/s; the design flow rate of the riser should not be less than 2.2m/s, and should not be greater than 10m/s;
(4 )? The flow velocity downstream of the transition of the siphon roof rainwater drainage pipe system should not be greater than 2.5m/s; when the flow velocity is greater than 2.5m/s, energy dissipation measures should be taken;
(5)? Standpipe pipe The diameter should be determined through calculation and can be smaller than the diameter of the upstream suspension pipe.
(6)? Siphonic rainwater buckets and roofs should be installed at the lowest point of the roof or gutter in each catchment area. The number of rainwater buckets in each catchment area should not be less than 2. The distance between two rainwater buckets should not be greater than 20m. The distance between the siphon rainwater bucket installed on the podium floor and the junction between the podium and the tower should not be less than 1m and should not be greater than 10m.
(7)? The shape of the gap between the siphon rainwater bucket anti-leaf cover and the grille can be hole-shaped or thin groove-shaped. The diameter of the hole-shaped gap opening should not be less than 6mm and should not be greater than 15mm.
(8)? For siphon rainwater buckets, the rainwater risers should be arranged symmetrically.
(9) When connecting multiple siphon rainwater buckets, the drainage connecting pipe of the siphon rainwater bucket should be connected to the suspension pipe and shall not be directly connected to the top of the rainwater riser.
(10) The starting depth of the gutter should be determined based on the water catchment area and slope of the roof and the water depth in front of the siphon rainwater bucket. The slope of the gutter should not be less than 0.003.
(11) The water crossing section of the gutter should be calculated and determined based on the design flow rate of the catchment area. The width of the gutter should ensure uniform water inflow around the rainwater.
(12) Pipes and fittings should be made of high-density polyethylene (HDPE) raw materials not lower than PE80 grade.
(13) The longitudinal retraction rate of the pipe should not be greater than 3%;
(14) The rainwater riser should be equipped with an inspection port according to the design requirements, and the center of the inspection port should be 1.0 from the ground m. When using high-density polyethylene (HDPE) pipes, the maximum distance between inspection ports should not be greater than 30m.
(15) Rainwater pipes should be installed according to the location specified in the design;
( 16) The connection between the connecting pipe and the suspension pipe should use a 45-degree tee;
(17) The connection between the suspension pipe and the riser pipe, and the riser pipe and the discharge pipe should use two 45-degree elbows or A 90-degree elbow with R not less than 4D.
(18) When high-density polyethylene pipes pass through walls, floors or parts with fire protection requirements, fire-retardant rings, fire-proof tapes or fire-proof casings should be installed in accordance with the design requirements;
(19) When rainwater pipes pass through walls and floors, metal or plastic sleeves should be installed. The top of the casing in the floor slab should be 20mm higher than the decorative floor, and the bottom should be flush with the bottom of the floor slab. The ends of the casing within the wall should be flush with the finish. The gap between the casing and the pipe should be filled with flame-retardant dense materials;
(20) During the installation process, the openings of the pipes and rainwater buckets should be temporarily blocked.
From the design principles of the siphon drainage system to the practical steps of its design, we understand what the siphon drainage system is from a conceptual level, and then try to simulate siphon from the practical steps Drainage pipe design. People have to admire the magic and power of this siphon drainage system after understanding how cleverly and quickly it can drain away accumulated water.
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