Abstract: Under the condition that the system and function of the sewage pumping station have been determined, the water hammer wave generated when the two pumps are stopped at the same time is calculated for the most unfavorable operating conditions, and the slow-closing check valve is determined according to the calculation result. Closing time and design strength of pipes and concrete structures. Key words: sewage pump station water hammer calculation slow-closing check valve
CLC number: TU992.25
Document identification code: C
Article ID: 1000-4602 (2001) 08-0048-02
1 Project Overview
Ningbo Beilun 4# sewage pumping station is located near the intersection of Songhuajiang Road and Mingzhou Road. The role of this pumping station in the planning is: an intermediate pumping station leading to the sewage treatment plant in the west of the Yanhe sewage system. However, the Gaotang Industrial Zone, which is located in the west of the Yanhe River, is attracting investment quickly. In particular, the production of the malt company requires the implementation of the sewage project west of the Yanhe River as soon as possible. Therefore, the 4# sewage pumping station is used as a drainage pumping station to meet the sewage discharge requirements of the Gaotang Industrial Zone. The design difficulty of this water delivery system is to determine the design pressure of the pipeline and the mixing chamber, and this pressure ultimately depends on the water hammer pressure. 2 design overview
The design and construction of the project is divided into two parts, namely: Beilun 4# sewage pumping station and 4# pumping station drainage pressure pipeline project. 6 sets of pumping stations: H=201.88kPa, Q=1660m3/h (4 with 2), currently installed 3 (2 with 1).
Underground pump room, the full length of the pressure pipe is 4060m, DN10000, and the diameter of the large pump outlet section is DN500.
Because the pressure pipe is to cross the river, the road has been built, the seawall, etc., there are siphon and inverted siphon sections, so it belongs to the water delivery system with large pump lift, long water pipeline and large elevation change. This kind of system is very prone to water hammer in actual operation, and the project belongs to the pump station and the pressure pipeline is designed separately, so no water hammer calculation is performed. However, from the perspective of safe operation and convenient maintenance of the pumping station, a slow-closing check valve is installed at the pump outlet, and a surge tank is installed at the pump station outlet, thereby reducing the water hammer pressure of the entire system and reducing the design pressure of the entire system. Save civil construction, equipment investment, and improve the safety of system operation. 3 water hammer calculation
3.1 Water hammer type discrimination
Ττ0=aυ0τ0/(2gH0)
Where μ is the water pipe characteristic constant, μ=aυ0/2gH0
Υ0——pipe flow rate when the valve is fully open, m/s
a——The water hammer velocity of the medium (when the medium is water, take a=1000 m/s)
H0——upper and lower head difference or pump head, kPa
Τ0—— dimensionless valve opening (τ0 is the initial opening)
When the valve is fully open, Ï„0=1.0, the flow rate of each pump is Q=1660m3/h, and the head H=201.88 kPa.
Because the most unfavorable working condition is that two pumps are powered off at the same time (currently 3 sets are installed in the pumping station, which is 2 for 1), then the flow velocity in the pipe is v0=1.174 2 m/s. When the head and the head difference H0=88.10 kPa, then μ=6.657, μτ0=6.657>1, which is a limit water hammer. When H0=201.88 kPa (pump head), μ=2.905, μτ0=2.905>1, which is a limit water hammer. 3.2 water hammer calculation
Use the following formula:
Hmax=(1+hm)H0
Hmax in the formula - maximum water hammer pressure, kPa
Hm - the maximum value of the maximum water hammer pressure
For the limit water hammer, hm=σ/2+[(σ+(σ2+4)1/2]
Σ——water pipe characteristic constant, σ=Lv0gH0Ts
L——pipe length, L=4 160 m
Ts - valve closing time, s
The water hammer calculation results are shown in Table 1.
Table 1 Water hammer calculation table
Head closure time
Ts=10s Ts=20s Ts=30s Ts=40s Ts=50s Ts=60 s H0=88.10 kPa σ=4160×1.1742 σ=2.769 σ=1.846 σ=1.385 σ=1.108 σ=0.923
/(9.81×8.99×10) hm=8.56 hm=4.22 hm=2.64 hm=1.88 hm=1.44
=5.539
Hm=5.539(5.539+ Hmax=842.21 Hmax=459. Hmax=320. Hmax=253.72 Hmax=215.01
(5.5392+4)0.5)/2 kPa 91 kPa 65kPa kPa kPa
=31.65
Hmax=(1+31.65)
×88.10=2876.46kPa H0=201.88 kPa σ=2.417 σ=1.209 σ=0.805 σ=0.604 σ=0.483 σ=0.40
Hm=6.71 hm=2.14 hm=1.19 hm=0.81 hm=0.61 hm=0.49
Hmax=1556.53 kPa Hmax=633.86 Hmax=442.07 Hmax=365.44Hmax=325.06 Hmax=300.76
Analysis of calculation results of kPa kPa kPa kPa kPa3.3
The working principle of HH44X-10 type slow closing valve used in Beilun 4# sewage pumping station is as follows:
Under the pressure of the inlet end medium, the valve flap automatically opens into position, and at the same time, the piston in the hydraulic cylinder rises to the highest position and the valve opens. When the pump is stopped or the medium stops flowing, the valve flap firstly closes to the slow-closing angle position under the self-weight and the return water pressure, and then slowly closes to the fully closed position, so as to stop the large amount of backflow of the medium and prevent the water from rising. The purpose of the pressure.
In addition, the slow-closed adjustment valve can be adjusted to adjust the length of the slow-closing time (that is, Ts can be adjusted), the slow-closing time is extended when the clockwise adjustment is made, and the slow-closing time is shortened when the counterclockwise adjustment is made.
Main performance parameters:
Nominal pressure: 1 MPa
Media flow rate: ≤ 5 m / s
Slow closing angle: 16°
The purpose of the water hammer calculation of the system is to find a suitable closing law, determine the valve closing time (Ts), determine the structural strength of the civil structure, determine the work of the pipeline design, test the pressure level, determine the height of the surge tank, and so on.
It can be seen from the water hammer calculation table: no matter the head difference between the upstream and the downstream, or the lift of the pump unit, the water hammer value in the pipeline is only when Ts ≥ 40 s, that is, when the valve is used for 40 s from full opening to full closing. Less than 320.65 kPa and 365.44 kPa, respectively.
According to the calculation result of water hammer, the water hammer pressure value of the head H=201.88 kPa and the closing time Ts=40 s should be selected as the larger value, and the mixing of the design pipeline and concrete structure of the 4# pumping station sea pressure pipe project is determined accordingly. The working pressure of the indoor part is 392.0 kPa, and the test pressure is 588.00 kPa, so that the pipe is determined as follows: the outlet section of the pumping station and the pipe bridge section adopt 14 mm thick steel pipe, and the end section of the pressure pipe adopts the prestressed concrete pipe of the socket interface.
4 Conclusion
During the commissioning of the 14# pumping station, it is recommended that the closing time of the slow-closing valve installed on the three units be determined as Ts ≥ 40 s.
2 During normal operation, it is forbidden to stop the two units at the same time.
3 In addition, regarding the selection of the check valve, attention should be paid to the closing law, preferably the second section is closed: the first section is closed to a small opening degree in a short time (16° is selected for this project), and then the rest is gradually closed. Opening degree. The system has been running smoothly for six years.
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