Calculation of Water Hammer at Sewage Pumping Station and Application of Slow Shut - off Valve

Abstract: Under the condition that the system and function of the sewage pump station have been confirmed, the water hammer wave generated when the two pumps are stopped at the same time is calculated under the most unfavorable working condition, and the slow closing check valve The closing time and the design strength of pipes and concrete structures. Key words: sewage pumping station water hammer calculation slow closing check valve 1 Project Overview Ningbo Beilun sewage pump # 4 The station is located near the intersection of Songhuajiang Road and Mingzhou Road. The pumping station plays a role in the planning as an intermediate pumping station to the sewage treatment plant in the sewage system west of the rocky river. However, currently located in the west of the Rocky River Gaotang Industrial Zone investment fast, especially the malt company put into operation, requiring the implementation of the west of the river rock discharge project as soon as possible. Therefore, 4 # sewage pumping station as a row of pumping stations to meet the high-Tang Industrial Zone sewage requirements. The design challenge of this water delivery system is to determine the design pressure of the pipe and mixing chamber, which 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, 4 # pumping station Pai Hai pressure pipe project. Pumping station installed 6: H = 201.88kPa, Q = 1660m3 / h (4 with 2 standby), currently installed 3 (2 with 1 standby). Underground pump room, pressure pipe length of 4060m, DN10000, large pump outlet section diameter of DN500. As the pressure pipe to cross the river along the way, seawalls, etc., with siphon, inverted siphon section, it belongs to the pump head large, long water pipelines, elevation changes in large water systems. This system is prone to water hammer in the actual operation, and the project belongs to the pump station and pressure pipeline separately designed, so there is no water hammer calculation. However, from the perspective of pump station operation safety and maintenance convenience, a slow-closing check valve is set at the outlet of the pump and a surge tank is provided at the outlet of the pump station, thereby reducing the water hammer pressure of the entire system and reducing the design pressure of the entire system to Save civil construction, equipment investment, improve system security. Elevation relations see Figure 1. Sewage pumping station water hammer calculation and slow closing check valve application 3 water hammer calculation 3.1 water hammer type discrimination μτ0 = aυ0τ0 / (2gH0) Where μ - water pipe constant, μ = aυ0 / 2gH0 υ0 - valve fully open When the medium flow rate of water hammer (medium is water, take a = 1000 m / s) H0 - upstream and downstream head difference or pump head, kPa τ0 - dimensionless valve opening (τ0 is the initial opening) When the valve is fully open, τ0 = 1.0, each pump flow Q = 1 660m3 / h, head H = 201.88 kPa. Because the most unfavorable conditions for the two pumps at the same time power (the current installed capacity of 3 pumping stations, 2 with 1 prepared), then the tube velocity v0 = 1.174 2 m / s. When the upstream and downstream head difference H0 = 88.10 kPa, then μ = 6.657, μτ0 = 6.657> 1, is the ultimate water hammer. When H0 = 201.88kPa (pump head), then μ = 2.905, μτ0 = 2.905> 1, is the ultimate water hammer. 3.2 Water Hammer Calculation The following formula is used: Hmax = (1 + hm) H0 where Hmax - the maximum water hammer pressure, kPa hm - the relative maximum water hammer pressure For the ultimate water hammer, hm = σ / 2 + [(σ + (Σ2 + 4) 1/2] Where σ - water pipe characteristic constant, σ = Lv0gH0Ts L - pipe length, L = 4 160 m Ts - valve closing time, s water hammer calculation results in Table 1. 1 Water Hammer Calculation Table Head Close Time Ts = 10s Ts = 20s Ts = 30s Ts = 40s Ts = 50s Ts = 60s H0 = 88.10kPa? = 4160 × 1.1742 / (9.81 × 8.99 × 10) = 5.539 hm = 5.539 ( 5.539+ (5.5392 + 4) 0.5) / 2 = 31.65 Hmax = (1 + 31.65) × 88.10 = 2876.46 kPa σ = 2.769 hm = 8.56 Hmax = 842.21 kPa σ = 1.846 hm = 4.22 Hmax = 459.91 kPa σ = 1.385 hm = 2.64Hmax = 320.65 kPa σ = 1.108hm = 1.88Hmax = 253.72 kPa σ = 0.923hm = 1.44Hmax = 215.01 kPa H0 = 201.88 kPa σ = 2.417hm = 6.71Hmax = 1556.53 kPa σ = 1.209hm = 2.14Hmax = 633.86 kPa σ = 0.805hm = 1.19Hmax = 442.07 kPa σ = 0.604hm = 0.81Hmax = 365.44 kPa σ = 0.483hm = 0.61Hmax = 325.06 kPa σ = 0.40hm = 0.49Hmax = 300.76 kPa 3.3 Calculation Analysis of Beilun 4 # sewage pumping station HH44X-10 slow-closing valve works as follows: At the inlet end of the medium pressure, the valve automatically opens in place, at the same time, the hydraulic cylinder piston to the highest position, the valve open. When the stop pump or media stop flowing, the valve flap under the weight and back pressure, first quickly closed to the slow corner position, and then slowly closed to the fully closed position, in order to achieve both stop the media back a lot, but also to prevent water hammer or The purpose of pressure.In addition, the slow closing valve can be adjusted to adjust the length of slow closing (that is, adjustable Ts), clockwise slow closing time prolongation, anti-clockwise adjustment slow closing time shorten the main performance parameters: Nominal pressure: 1 MPa Medium flow rate: ≤5 m / s Slow closing angle: 16 ° The purpose of the system is to find the proper closing law and to determine the valve closing time (Ts) so as to determine the design strength of the civil structure and to determine the design of the pipeline Work, test pressure level, determine the height of surge tank and so on. Through the water hammer calculation table can be seen: both upstream and downstream of the head difference, or pump head, only when Ts ≥ 40 s, the valve from full open to fully closed with 40 s, the water hammer in the pipe value Respectively less than 320.65 kPa and 365.44 kPa. According to the calculation results of water hammer, the water hammer pressure value should be larger when the head H = 201.88 kPa and the closing time Ts = 40 s, so as to determine the design pipeline and concrete structure mix of Paihai pressure pipe project of 4 # pumping station The working pressure inside the chamber was 392.0 kPa and the test pressure was 588.00 kPa. Thus, the pipe was determined to be: outlet section of pump station, 14 mm thick steel pipe in pipe section, and prestressed concrete pipe with socket interface in the tip section of pressure pipe. 4 Conclusions ① During the debugging of Pump Station # 4, it is suggested that the closing time of the slow-closing valve installed on the three units be determined as Ts≥40 s. ② During normal operation, 2 units are prohibited from stopping at the same time. ③ In addition, on the choice of check valve, should pay attention to the closure of the law, preferably closed for the second paragraph: the first paragraph in a relatively short period of time the valve flap to a small opening (the project selected 16 °), and then slowly closed the rest Opening Six years of system operation, has been stable and normal.