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Discussion on the problem of adding the exhaust valve in the pipeline
发布时间:2015-8-29 20:54:56 作者: 信息来源: 点击:

I. Introduction

Water delivery pipe, mainly refers to the water source to the water or water purification plant to the water supply pipeline network. Because of the water supply pipeline, and the pressure is higher, so its safe operation is always from the water department and the design department to pay attention to the common accident is the pipe, the cause of the explosion pipe is: temperature stress, pipe quality, construction quality, quality structure and water hammer, etc.. Air bag in the pipeline can not directly cause water hammer, but can be caused by water hammer damage. In this paper, we discuss how to set up the exhaust valve in the pipeline to avoid gas accumulation and air - gas - air - gas - air - air - air - air - air.

Two, examples and analysis of the terrain in the area, the highest point of the water pipe is located in the exhaust valve, but the actual operation, many of the tubes did not occur in the high or low, but after the high point of the lower pipe section, and even the low pressure pipe is also such a tube. A typical example of a pipe burst in Hegang, Heilongjiang. Exhaust pipe burst, but continuous DN800 Hegang municipal low mountain and hilly region, the net water and water pumping station building, a distance of 5 km, purified water by gravity flow to water pumping stations, water purification plants clean the pool elevation 210m, water pumping station in the cleaning water tank height 185m, water pipe cast iron pipe, the average velocity 1.0m/s pumping station 500m a Gaogang, elevation 185 (see Figure 1), Takaoka, the highest point of an exhaust valve exhaust valve after 50m, repeated tube burst accident. Later in the tube fitted with a pair of exhaust valve, a few years, the two exhaust valve without explodes again, only in the newly installed valve 10m occurs at a time explosive tube. In this case, the gas in the tube is related to the gas in the tube (the arrangement of the air valve is not explosive).

The forming process of the air bag in the duct and the force of it are analyzed. The 1 gas gathering and balance in normal condition, the water flow in the pipeline can be regarded as constant current (pressure, flow rate and temperature). In this state, the gas in the water is gradually separated, and the size of the bubbles rise to the tube wall, and the bubble is moved forward by the flow velocity. In the upper part of the slope, the bubble velocity may be greater than the water flow due to buoyancy. Because of the roughness of the tube wall, the bubble movement direction is same, it is difficult to get together with large bubbles. Small bubbles flow along the wall of a certain width, through the highest point of the exhaust valve, the diameter of the exhaust pipe diameter of the bubble is discharged, and other bubbles by the flow of the thrust of the downward flow. Due to pipe wall and tangential turbulence and flow characteristics, so that some small bubbles through the exhaust vent over also downstream to flow across the exhaust valve of bubbles along the slope in the opposite direction, the motion direction and the bubble by buoyancy force P1 direction opposite, the buoyancy force generated resistance, it is inevitable that slow down the speed of moving bubble, bubble sequence likely to hit the front of the bubble and the whole big bubbles, the bubbles generated a large buoyancy. Buoyancy force p1=psin alpha (1) TD\\QXK168 type in: P - bubble by water buoyancy (p=1/6 PI D3 - P) P - water of bubble of bulk vo=B#8d-- diameter /bv-Fsa3~f alpha pipeline depression: bubble CWfL}|[[Z by the pushing force of water flow for P v2T1D'cU -9p'=-----. (2) SX+=$h% type in: ------- velocity pressure (kg / cm2) x X_kS| Nfb^.=5 were 1?.,

Bubble - the largest cross-sectional area (s=1/4 PI D2) flow of /v-- speed (M / s) 0n* when P1 = p`, bubbles force balance and still in the pipeline. Simultaneous (1), (2) d.sin alpha 10.4p.gLtWPY_ were =11c-- equilibrium constant QeJSC. 3. Type (3), inversely the sine of the pipeline diameter and angle of bubble under constant flow strip. When the sin - D - >c, the bubble moves upwards. When the bubble equilibrium of the air sac in the pipeline is 2, the bubble is assumed to be equal to D. This can only be described as small bubbles, and the bubbles can reach a certain volume and rise to the tube wall. As the bubble grows, the bubble shape will be controlled by thrust, gravity and water pipe shape, greater elongation in the length direction, the transverse arch according to the simulated measurement, the relationship of long l and airbag for 1 h is 15hvi3. air force analysis and critical position of A|H+h according to the principle of water conservancy, water balloon in the pipeline in the balance of thrust, is equal to the cross section perpendicular to the flow of the pressure, this section is based on H Vn V2 L]Mp'= high arch Sigma pi= -----.s (5) at 1 2g10z..7| |xls-- caused by tube explosion in bow product is due to airbag can quickly open, close the valve or pump start and stop, make out the pipeline the pressure value, the gas compressibility characteristics, the stress concentration to produce high-pressure balloon and burst pipe. According to the experience of some of the tube, the air bag height to diameter 1/4 is the risk point of the tube, it is the critical point of the balloon. When the volume of the airbag and the basal area of simple calculation: v = 0.5 s = 0.2 PI R3, PI r2. -2ts018^0 of precedent in DN800 pipeline, when the v=1.0m/s. The by the thrust is calculated according to (5): VDaoK1.02Dj-qKEUi6p'= Pi ------0.2.402=5.124 (kg) *2g buoyancy according to formula (1) calculation ap1=psin alpha = 0.5 PI 0.43 * 1000sin alpha =100.5sin alpha when p`=p1? 5.214K&t% alpha =arcsin= -----------=2.92 degrees 100.5NEQO the depression of the alpha and the measured detonation tube point depression are basically consistent.

Conclusion 1. Conduit downhill section must install the exhaust valve, the specific location is determined by the alpha p`=psin, velocity calculation taking average value should be 2. Actual pipe angle less than the calculated angle, exhaust valve should be located in the bending curve and the straight line at the intersection of; 3. In order to make the gas inside the tube early discharge without the formation of airbag, the intersection of the bent pipe and straight pipe line shall be set up exhaust valve; 4.


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