CC BY
10
Mamajonov Makhmud, Shakirov Bakhtiyar Makhmudovich, teachers, of Andijan branch of Tashkent State Agrarian university Shakirov Bobur Mirzo Bakhtiyar ogli, Andijan machine building institute E-mail: [email protected]
FORECASTING FACTORS AFFECTING THE WATER PREVENTION
OF CENTRIFUGAL PUMPS
Abstract: The results of full-scale studies on the study of the operating modes of centrifugal pumps for determining factors affecting the reduction of their water supply are presented in the article. Keywords: pump, feed, head, pipeline, flow, wear.
In irrigation systems of the Republic of Uzbekistan, more than 50% of the area is irrigated using pumping stations, the number of which is 1618, where more than 5,000 pumping units are installed with a total feed of6535 ... 6600 m3/s and a capacity of3577 mVt. One of the largest electricity consumers in agriculture (more than 70%) is the paddle and axial pumping units, most of which are used in agriculture, industry and communal services.
Experience in the operation of pumping stations has shown that many of them work with the supply much lower than the design ones. The main reasons for this are the unsatisfactory hydraulic regime of the water intake structures and the wear of the elements of the flow-through part of the pumps [1, 19-24].
In order to assess the effect of hydraulic processes occurring in the water supply and water supply facilities and the hydro mechanical processes occurring inside the pump on reducing its water supply, tests were carried out of units 1 and 2 of the pumping station " Turakurgan-1" and units 6 and 7 of the pumping station Irrigator (Namangan region) equipped with the same centrifugal pumps of grade D4000-95 (22NDs with n = 730 rev/min). Measurements and calculations of the main technical parameters of pumps were carried out on the basis of the existing standard research methodology [2, 328-333].
To determine the pump head, we used model vacuum gauges and pressure gauges connected respectively to the suction and discharge nozzles, the water supply was determined from the value of the flow velocity in the pipeline, measured with the help of the Pito's tube, the shaft power was calculated from the formula based on the voltmeter and ammeter readings, shaft was measured with a tachometer [3, 60-65]. Loss of head of the suction pipeline was determined by the indications of two vacuum gauges, the first installed in the initial section after the rotation of the pipeline axis, and the second in the inlet pipe of the pump [4, 58-59].
The loss of the head of the suction line was calculated by the formula:
V2
hw = hvac - hs - — (1)
2g
where vac is the reading of vacuum gages No. 1 or No. 2;
hs - is the geodetic height from the level of the downstream to the point
Connection of vacuum gauges;
V-is the flow velocity at the pressure measurement point. The resistance coefficient of the suction pipe was determined from the following expression:
h. ■ 2g
V2
(2)
Figure 1 shows a comparison of the factory characteristics with the full-scale test data of the 1 st Turakurgan-1 pumping station. As can be seen from Picture 1, the experimental points are slightly lower from the pressure line of the factory characteristic, although the pump consumes sufficient power. With the valve fully open, the head of the pump is HB = 54.8 m, the water supply was Q = 698 l/s instead of the design Qa = 1000 l/s, i.e. the working point A was shifted to point B and the difference was AQ = 302 l/s. Because of the reduced water supply, the efficiency of the pump was lower by 12 ... 15% [5, 77-80].
The displacement of the design work point A to the actual operating point B in Picture 1 depends on many factors, the degree of their influence on the water supply reduction can be established by conducting a detailed analysis of all the technical parameters of the pump, as well as the suction and pressure pipelines.
Figure 2 shows the dependence of the resistance coefficient on the water supply of the pump with the water intake chamber clogged and after its partial washing. Partial washing of sediment deposition in the chamber was achieved by increasing the bottom flow velocities, forming a gap
by covering the upper part of it with the help of wooden shields. As can be seen from Figure 2, the coefficient of hydraulic resistance of the suction pipeline Z decreases in all operating modes of the pump after partial washing
of the water intake chamber. As a result of the decrease in hydraulic resistance, the pump supply increased from Q = 698 l/s to Q = 738 l/s, i. e. at qc = 40 l/s (see Figur 1) [6, 119-128].
H, n
60 55 50 45
1
I Hp Hp Hp h le
0
o E tr A__
K is- "-Ha N HÎ s^H
q= v '... r ^COn q. N '
* Ö — a
90 80 70
N,
kVt 600
400
500
600
700
300
900
1000
Figure 1. Comparison of the design mode of operation of the pump D4000-95 with the data of full-scale tests: H, N, p - pressure curves, power and efficiency according to the factory characteristic, Hp, Hp1, Hp11, Hp111 - hydrodynamic curves, A - design operating point, V and C - respectively, operating points before and after washing the water intake chamber (according to field tests), A1, A2, Ag, D - predicted operating points
After washing the chamber between the hydrodynamic curve and the design curve, there was still a significant difference, i.e. the difference in head between points S and E has a significant value, which convinces of increased values of head loss in pipelines. To determine the actual values of the head loss in suction pipelines, the readings of two vacuum gauges installed in the initial and final sections were used. Multiple measurements of the vacuum values in the suction pipelines
of the 1st and 2nd units were made. According to the measurement data, the pressure losses were calculated between the sections of the suction piping pressure measurement, which was h = 2.9 ... 3.5 m, and the calculation should be h = 0.53
sp 1 sp
m (difference in head Hc- HE = h'p in Figur 1.) [7, 12-18].
The values h'sp and h show that cleaning of the suction pipe is required, and thus it is possible to increase the pump supply to Q = 800 l/c (ie, another qs = 62 l/s).
Figure 2. Dependence of the resistance coefficient of the suction pipeline from the water supply of the centrifugal pump: 1 and 2 - respectively curves obtained before and after washing the water intake chamber
As indicated by the pressure gauge installed on the pump discharge connection, the actual values of the pressure loss of the discharge line were found, and this value was checked by calculation. The difference between the calculated and actual value of the head loss is Ahh = 0.85 m (the difference in head between points D and K in Figur 1), which was associated with the accumulation of air at elevated points of the pressure pipeline. Hence, with the removal of air from the individual sections of the discharge pipeline, it is possible to increase the pump supply to QA3 = 815 l/s (ie, for qpp = 15 l/s).
To determine the reasons for the reduction in the water supply of the pump associated with the hydromechanical processes occurring inside the pump, it is necessary to consider the change in the pump characteristic between the points A and A3 along the hydrodynamic curve Hp = f(Q) (see Figur Surfaces of the flowing part of the pump during long operation (more than 15 years) are exposed to the hard abrasive particles present in the pumped water and have a flake-like undulating shape, which leads to an increase in frictional pressure loss. Carrying out calculations by the appropriate method, the total value of the head loss of the flow-through part of the pump is determined: hp = 3.23 m. In (Fig. 1), we find the points O and A , the difference in heads of which corresponds to the value of the head loss of the flow part hp = 3.23 m. Accordingly, the decrease in water supply by increasing the hydraulic resistance of the flow-through part of the pump is
qw = QA-QA1 = 1000-935 = 65 l/s [3, 60-65].
If the initial clearance between the impeller disk and the sealing ring was equal to So = 0.7 mm, at the time of the test it was S = 2.72 mm. Calculations using the method described in the works show that the increase in water leakage through sealing gaps on both sides of the impeller will be equal to ql = 90 l/s [5, 77-80].
Putting the value of qy from the point A on the pump characteristic (see Figur 1), we find the point A2. As can be seen, there is a difference qa = 30 l/s between point A2 and A3, which means an increase in the amount of water leakage through the clearance between the "language" of the outlet device and the impeller, and also in the stuffing box. The permissible gap in the area of the "language" should be Slang = (0,03 ... 0,05) x D2 = 0,05 x 860 = 43 mm. With long-term operation (more than 15 years), the actual gap in the area of the "language" increased to Slng = 78 mm, which is the reason for an increase in reverse leakage through this gap.
The increase in the hydraulic resistance of the suction line (qc + qsp = 10.2% and the increase in the gaps in the seals and in the "tongue" region qcom + qlnn = 12%) has the greatest impact on the decrease in the water supply of the pump.
As can be seen from (Table 1), the increase in hydraulic resistance of the suction line (qc + qp = 10.2% and the increase in the gaps in the seals and in the "language" region qom+qkn = 12%) has the greatest effect on reducing the water supply of the pump.
Table 1. - Degree of reduction of water supply of pump D4000-95 in dependence from various factors
Description of quantities Notation Unit. amendment Number of Decrease in water supply of the pump%
Reduction of water supply due to siltation of the water intake chamber. 1c l/s 40 4
Reduced water supply due to increased hydraulic resistance of the suction pipeline. tf-sp l/s 62 6.2
Decrease in water supply due to increased hydraulic resistance of the pressure pipeline. %rp l/s 15 1.5
Decrease in water supply due to increased gap in the area of «language». han l/s 30 3
Reducing water suppression increase the sealing gap of the impeller. 1 J-com l/s 90 9
Decrease in water supply due to increased hydraulic resistance of the flowing part of the pump. 1 J-W l/s 65 6.5
Total reduction in water supply of the pump. AQ l/s 302 30.2
It should be noted that, depending on the operating conditions of the pumping station, the percentage of reduction in the water supply of the pump, depending on the individual factors, can be different.
Based on the foregoing analysis, it follows that it is required to develop a set of specific measures to improve the design of water intake facilities, as well as to reduce wear on the parts of the flow passage and the sealing elements of the pump impeller.
References:
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2. Chebaevsky V. F., Vishnevsky K. P., Nakladov N. N. Designing pumping stations and testing pumping plants.- Moscow.: Kolos.-2000.- P. 328-333.
3. Beglov I. F., Glovatsky O. Ya., Talipov Sh. G. Analysis of fault diagnosis systems for pumping units: Sat. sci. Tr. SIC ICWC.-2001.- P. 60-65.
4. Kiselev P. G. Handbook of hydraulic calculations.- M. Energia.- 1974.- P. 58-59.
5. Mamazhonov M. Analysis of operational conditions of pumping stations for agricultural purposes / Bulletin of Agrarian Science of Uzbekistan. Tashkent State University - Tashkent: - 2004.- No. 1.- C. 77-80.
6. Polovets A. L., Ishutinov E. M. Study of the supplying devices of pumping stations of drainage systems: Sat. sci. Tr. V / O "Soyuzvodproekt". - M.: - 1982.- No. 59.- C. 119-128.
7. Glovatsky O. Ya. Theory and methods of control of hydraulic processes in the operation of reclamation pumping stations: Author's abstract. Dis. ... doc.techn. sciences.- Moscow: MISI.- 1989.- P. 12-18.
