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泵試驗的目的和采 用的標準
一、試驗目的
泵的性能及性能曲線迄今為止還不能用數(shù)學方法來精確推算出來，只能通過泵的試驗來確定。對于新設計的泵或泵的某項目的科研，通過泵的試驗來驗證是否達到了預期的要求，得出正確的性能參數(shù)，做出性能曲線圖，一般都是在實驗室內進行，必要時須現(xiàn)場進行測試。而對于老產品通過試驗來保證泵的質量(即出廠試驗)或驗證合同中用戶提出的要求( 即驗收試驗)，驗收試驗的內容、方法、精度、地點等由雙方簽訂的合同或協(xié)議中明確進行規(guī)定，試驗地點可在制造廠的實驗室內，也可在需方使用現(xiàn)場或在第三方實驗室內進行。
二、目前泵試驗采用的標準
試驗采用的標準是隨技術的發(fā)展是經常變更的，下面列舉出目前離心泵試驗所采用的主要試驗標準。
(1)《回轉動力泵水力性能驗收試驗1級和2級》(CB/T 3216- 2005)
(2)《水泵流量的測定方法》(GB/T 3214- -2007)
(3)《泵的振動測量與評價方法》(JB/T 8097- 1999)
(4)《泵的噪聲測量與評價方法》(B/T 8098- 1999)
第二節(jié)泵試驗種類和方法
泵的試驗按試驗內容可分為運行試驗、性能試驗、汽蝕試驗、 四象限試驗、水泵模型及裝置模型試驗等。
一、 泵的運行試驗
泵的運行試驗一般分為磨合性運行試驗和可靠性模擬運行試驗。
1. 磨合性運行試驗
泵在規(guī)定點(設計點)運行工況下，檢查泵的振動和噪聲是否符合要求;檢查泵的軸承及軸封處的溫升是否符合要求;檢查軸封泄漏量;停泵后檢查泵的密封環(huán)、軸承、軸套、平衡裝置等的磨損情況。磨合運行試驗要求有一定持續(xù)運行時間后 再進行檢查，如表8 - 1所示。
2.可靠性模擬運行試驗
根據用戶現(xiàn)場的使用條件，在制造廠的試驗臺上進行較長時間的運行試驗?？?/span>靠性模擬運行試驗一般是用于使用工況非常特殊:試驗內容超出常規(guī)的試驗要求(可能遇到的危險因素)；試驗介質的性質、 試驗溫度及壓力有特殊要求的場合下的就驗，需在供貨合同或協(xié)議議中進行明確的規(guī)定。
二、泵的性能試驗
泵的性能試驗是通過試驗方法測得泵的主要性能參數(shù)值，如流量Q、 揚程H、泵的輸入功率P (軸功率)、轉速n和通過計算得到的泵的輸出功率Pu(有效功率)和泵的效率η等值，以及他們之間的關系曲線Q - H曲線、Q-P曲線、Q-”曲線。
1.性能試驗方法
泵的性能試驗前，先要進行泵的磨合性試驗，并還要進行穩(wěn)定性檢查。穩(wěn)定性檢查包括讀數(shù)波動性檢查和重復檢查，波動幅度應符合表8 -2所規(guī)定的范圍，重復性應符合表8-3的規(guī)定范圍。
所謂讀數(shù)波動是指在一次讀數(shù)的時間內， 讀數(shù)相對于平均值的變動，波動值的計算公式:
最大讀數(shù)值-平均讀數(shù)值/平均讀數(shù)值x100%
最小讀數(shù)值一平均讀數(shù)值/平均讀數(shù)值x 100%
所謂重復性是同一量(除只有轉速和溫度允許進行調整外。其余如節(jié)流閥、水位、填料函、平衡水等所有調節(jié)位置應完全保持不交的情況下的同量)相鄰兩次茂數(shù)尚(對排一試驗點應以隨機的時間間隔不少于10s的相鄰兩次讀數(shù))的變化。對每一個試驗工況點，最低限度應取3組讀數(shù)，并應記錄每一個獨立讀數(shù)的值和由每組讀數(shù)導出的效率值。每一量的最大值與最小值的百分率差不得大于表8 -3給出的值。需要注意，如果讀數(shù)增加，則允許有較大的相差。
重復性值計算公式為:
最大值-最小值/最大值x100%
上述檢查完后，可以進行性能試驗，試驗時，可以通過調節(jié)出口調節(jié)閥來得到不同的流量點，一般要求從關死點 (Q=0) 到最大流量點(0=1.40)之間包括規(guī)定點(設計點)在內的13個以上的流量點進行測試，每一個流量點記錄下相關的數(shù)值，例如流量、壓力、真空度、轉速、功率等數(shù)值，然后計算出泵的流量、揚程、 轉速、輸出功率、輸入功率、效率等。最后按式(2-39)、式(2-40)、式(2-41)比例定律換算到規(guī)定轉速下的性能參數(shù)，并將性能參數(shù)繪成泵的性能曲線。
2.試驗液體
對輸送非清潔冷水液體的泵，可以用清潔冷水來進行泵的性能試驗，然后換算到相應液體的性能。
3.試驗轉速
因受試驗條件限制，試驗轉速可能與規(guī)定轉速不一致，可以通過比例定律，將試驗性能換算到規(guī)定轉速的性能。但不能相差太大，否則會帶來較大的誤差。標準規(guī)定，在流量和揚程的測量時，對試驗精度為1級和2級時，試驗轉速在規(guī)定轉速的50%到120%的范圍內進行，對試驗精度為精密級時，試驗轉速在規(guī)定轉速的80% ~ 120%的范圍內進行。在泵的輸人功率測量時，不論是1級、2級還是精密級，都規(guī)定試驗轉速在規(guī)定轉速的80% ~ 120%的范圍內進行。
4.試驗精度
泵的試驗精度分為精密級(A級)、 1級(B級)、2級(C級)三種。不同的精度要求，泵各性能參數(shù)測量的不確定度容許值是不同的。表8-4表示了深各個性能參數(shù)總的測最不確定度答許值，表8 -5表示了泵的效率總的不確定度導出值的容許值。
從表8-5中可以看出，精密級精度最高，測量儀表常需要原位標定，試驗較難達到，所以只有在特殊要求下采用。1級精度較高，可用于檢測中心、重要新產品、重大科研項目測試鑒定等的試驗。2級精度較低，可用于泵生產廠常規(guī)的出廠試驗。
5.容差系數(shù)
由于泵在制造過程中，必定會產生偏差，渣漿泵所以每臺泵產品都可能會發(fā)生幾何形狀和尺寸不符合圖樣的可能，故在對試驗結果與保證值(工作點)進行比較時，應允許有一定的容差值存在，泵的這些容差，只與實際的泵有關，并不涉及試驗條件和測量不確定度。
容差系數(shù)士tq， 土ty，土In分別為流量、揚程和效率的容差系數(shù)值，如表8-6所示，用于保證點Qc、He保證點Qc、H。由合同或協(xié)議中規(guī)定，如無規(guī)定，通常情況下即為泵的規(guī)定點(設計點)。
6.保證的證實
試驗所得到的結果是否達到了供貨合同或協(xié)議書中規(guī)定的保證值(包括它們的容差)，也即判別泵是否達到了性能的要求，這就是保證的證實。
(1)泵流量、揚程保證的證實:
將測量得到的結果換算到規(guī)定轉速，然后繪制出Q -H的關系曲線( 與各測量點擬合成最佳的曲線代表泵的性能曲線)，如圖8-1所示。
通過保證點(lc、 He)作水平線段士t0 .Q。和作垂直線段土1日. He的容差“+”字線。
如果Q-H曲線與“+”字線相交或至少相切，則認為泵的流量和揚程已得到了保證，泵的流量和揚程判別為合格。
(2)泵效率保證的證實:
泵試驗的效率值是由通過規(guī)定的保證點Qc、He和坐標軸原點所作的連線，與實際試驗測得的Q-H曲線相交的交點，作的一條垂線 與實際測得的Q一η曲線相交的交點的效率值為此泵的效率值。如果該效率值高于或至少等于ne.(1 -t,)的值，則認為泵的效率是在容差范圍內，認為泵的效率合格。如圖8-1所示。
如果測得的流量Q、揚程H值大于保證值Qc，Hc: 但仍在容差范圍內，且效率也在容差范圍內，泵雖然是合格的，但要注意此時實際的輸人功率可能要大些，要注意原動機功率的配備情況是否夠大。
如果泵的流量、揚程測得的比規(guī)定的高，已超出了上容差范圍時，可通過車削葉輪直徑來進行修正，對型式數(shù)K≤1. 5的泵，直徑車削不超過5%，車削后的性能可用下式來計算(車削后不需要重新做實驗):
式中下標r代表切削后的，1代表試驗的，D2、D.、D:如圖8-2所示。型式數(shù)K:
對型式數(shù)K≤1.0的泵，葉輪直徑車削不大于3%時，可認為車削后工作點的效率不變。
Purpose and standard of pump test
I. test purpose
So far, the performance and performance curve of the pump can not be accurately calculated by mathematical method, but can only be determined by the pump test. For the scientific research of a newly designed pump or a certain project of the pump, the test of the pump is used to verify whether the expected requirements have been met, the correct performance parameters are obtained, and the performance curve is drawn, which is generally carried out in the laboratory. If necessary, the field test is required. For the old products, the quality of the pump (i.e. delivery test) can be guaranteed by test or the requirements of the user in the verification contract (i.e. acceptance test). The content, method, accuracy and location of the acceptance test shall be clearly specified in the contract or agreement signed by both parties. The test location can be in the laboratory of the manufacturer, the user's site or the third party's laboratory.
II. Current pump test standards
The standards used in the test are often changed with the development of technology. The main test standards used in the current centrifugal pump test are listed below.
(1) level 1 and level 2 hydraulic performance acceptance test of rotary power pump (CB / T 3216-2005)
(2) measurement method of water pump flow (GB / T 3214-2007)
(3) vibration measurement and evaluation method of pump (JB / T 8097-1999)
(4) measurement and evaluation method of pump noise (B / T 8098-1999)
Section II type and method of pump test
According to the test contents, the pump test can be divided into operation test, performance test, cavitation test, four quadrant test, pump model and device model test, etc.
I. operation test of pump
The running test of pump is generally divided into running in test and reliability simulation test.
1. Running in test
Under the operating condition of the pump at the specified point (design point), check whether the vibration and noise of the pump meet the requirements; check whether the temperature rise of the bearing and shaft seal of the pump meet the requirements; check the leakage of the shaft seal; check the wear of the sealing ring, bearing, shaft sleeve, balance device, etc. of the pump after stopping the pump. Running in operation test requires a certain duration of operation before inspection, as shown in table 8-1.
2. Reliability simulation operation test
According to the use conditions of the user's site, a long-term operation test is carried out on the test bench of the manufacturer. Reliability simulation operation test is generally used for very special working conditions: the test content exceeds the conventional test requirements (possible risk factors); the test shall be carried out when the nature of test medium, test temperature and pressure have special requirements, which shall be clearly specified in the supply contract or agreement.
II. Pump performance test
The performance test of the pump is to measure the main performance parameters of the pump through the test method, such as flow Q, head h, input power P (shaft power), rotation speed n of the pump, the equivalent value of output power Pu (effective power) and pump efficiency η obtained through calculation, as well as the relationship curve Q-H curve, Q-P curve and Q - "curve between them.
1. Performance test method
Before the performance test of the pump, the running in test of the pump shall be carried out first, and the stability inspection shall also be carried out. The stability inspection includes reading fluctuation inspection and repeated inspection. The fluctuation amplitude shall meet the range specified in table 8-2, and the repeatability shall meet the range specified in table 8-3.
The so-called reading fluctuation refers to the change of the reading relative to the average value in the time of a reading, and the calculation formula of the fluctuation value:
Maximum reading value - average reading value / average reading value X100%
Minimum reading value - average reading value / average reading value x 100%
The so-called repeatability is the same amount (except that only the speed and temperature can be adjusted). Other adjustment positions such as throttle valve, water level, stuffing box, balance water, etc. shall be kept in the same amount when they are not intersected completely) the change of the adjacent two times of Mao number (the adjacent two readings of the first row of test points shall be no less than 10s at random time interval). For each test condition point, at least 3 groups of readings shall be taken, and the value of each independent reading and the efficiency value derived from each group of readings shall be recorded. The percentage difference between the maximum value and the minimum value of each quantity shall not be greater than the value given in table 8-3. It should be noted that a large difference is allowed if the reading increases.
The calculation formula of repeatability value is:
Max min / max X100%
After the above inspection, the performance test can be carried out. During the test, different flow points can be obtained by adjusting the outlet regulating valve. Generally, more than 13 flow points, including the specified point (design point), are required to be tested from the dead point (q = 0) to the maximum flow point (0 = 1.40). Each flow point records the relevant values, such as flow, pressure, vacuum degree, speed Then calculate the flow, head, speed, output power, input power and efficiency of the pump. Finally, according to the law of proportion of formula (2-39), formula (2-40) and formula (2-41), the performance parameters are converted to the performance parameters at the specified speed, and the performance parameters are drawn into the performance curve of the pump.
2. Test liquid
For the pump conveying non clean cold water liquid, clean cold water can be used for performance test of the pump, and then converted to the performance of the corresponding liquid.
3. Test speed
Due to the limitation of the test conditions, the test speed may be inconsistent with the specified speed. The test performance can be converted to the performance of the specified speed through the law of proportion. However, the difference should not be too large, otherwise it will bring a large error. According to the standard, when measuring the flow and head, when the test accuracy is level 1 and level 2, the test speed shall be within the range of 50% to 120% of the specified speed, and when the test accuracy is precision level, the test speed shall be within the range of
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