METHOD FOR IDENTIFICATION OF IMPELLER WEAR AND EXCESSIVE WEAR-RING CLEARANCE IN CENTRIFUGAL PUMPS

Abstract

A method for determining mechanical degradation of parts of a centrifugal pump having a fluid inlet, an impeller, and a fluid outlet. The method includes calculating at least one of a wear-ring clearance effect and an impeller wear effect. The wear-ring clearance effect is calculated using measurements of an actual pump flow rate Qp and actual pump power Pwp, calculating an internal flow rate of the pump Qp.sub.Pwp, calculating the mechanical power Pw.sub.Qp that should be used if the pump worked as specified in a theoretical curve, and calculating a difference between a theoretical Head and an internal Head Hp.sub.th?Hp.sub.Pwp to obtain the loss of Head due to the wear-ring clearance. The impeller wear effect is calculated by measuring an actual input pressure p.sub.in, an actual output pressure p.sub.out and an actual pump power Pwp, calculating a theoretical flow rate QpPwp corresponding to the measured mechanical power Pwp, calculating a theoretical Pump Head HpPwp, calculating the actual Pump Head Hp from the actual input pressure p.sub.in, and the actual output pressure p.sub.out and a pumped fluid density, and calculating a difference between the theoretical pump head and the actual pump Head HpPwp?Hp to obtain the loss of head due to the impeller wear.

Claims

1. A method for determining mechanical degradation of parts of a centrifugal pump having a fluid inlet, an impeller and a fluid outlet, comprising: calculating at least one of a wear-ring clearance effect and an impeller wear effect where: calculating said wear-ring clearance effect is done through: measuring an actual pump flow rate Op and actual pump power Pwp, calculating an internal flow rate of the pump Qp.sub.Pwp through projecting said actual pump power Pwp on a theoretical Pump Mechanical power versus Pump Flow rate curve at iso mechanical power, calculating the mechanical power Pw.sub.Qp that should be used if the pump worked as specified in the theoretical curve through projecting said actual pump flow rate on said theoretical Pump Mechanical Power versus Pump Flow rate curve at iso flow rate, applying the measured flow rate Op on a theoretical Pump Head versus Pump Flow rate curve to obtain a theoretical Head Hp.sub.th, applying the internal flow rate of the pump Qp.sub.Pwp on said theoretical Pump Head versus Pump Flow rate curve to obtain an internal Head Hp.sub.Pwp, calculating a difference between said theoretical Head and said internal Head Hp.sub.th?Hp.sub.Pwp to obtain the loss of Head due to the wear-ring clearance; and where: calculating said impeller wear effect is done through: measuring an actual input pressure pin, an actual output pressure pout and an actual pump power Pwp, calculating a theoretical flow rate Qp.sub.Pwp corresponding to the measured mechanical power Pwp on a theoretical pump characteristic Pump Power versus Pump Flow rate curve, projecting such theoretical flow rate QpPwp on a theoretical Pump Head versus Pump Flow rate curve at iso-pump flow rate ?Q=0 to obtain a theoretical Pump Head HpPwp, calculating the actual Pump Head Hp from the actual input pressure p.sub.in, and the actual output pressure p.sub.out and a pumped fluid density, calculating a difference between said theoretical pump head and said actual pump Head HpPwp?Hp to obtain the loss of head due to the impeller wear.

2. The method according to claim 1 comprising calculating a flow rate inside the pump $Q_{p_{\mathrm{pump}}}={\mathrm{Qp}}_{\mathrm{Pwp}}=\mathrm{Qp}+?Q,$ where ?Q is the additional flow rate due to the increasing of the wear-ring clearance compared to the initial status of the pump that is provided by the theoretical Pump Head versus Flow rate curve, and considering that at the pump head Hp.sub.Pwp corresponding to the measured power and at iso-Pump Head H=H.sub.th=Hp.sub.Pwp the Hydraulic efficiency being equal to 1, setting a hydraulic efficiency at: ${?}_{\mathrm{HY}}=\frac{H}{H_{\mathrm{th}}}=1,$ the method comprising: calculating a mechanical efficiency: ${?}_m=\frac{P_I}{P_s}=\frac{?.Math.g.Math.{\mathrm{Hp}}_{\mathrm{Pwp}}\left(Q_p+?Q\right)}{{\mathrm{Pw}}_p}$ calculating a volumetric efficiency: ${?}_v=\frac{Q_p}{\left(Q_p+?Q\right)}$ and calculating the efficiency of the pump with pump wear-ring clearance impact ${?}_{\mathrm{wearRing}}={?}_m?{?}_{\mathrm{HY}}?{?}_v=\frac{?.Math.g.Math.{\mathrm{Hp}}_{\mathrm{Pwp}}.Math.Q_p}{{\mathrm{Pw}}_p}$

3. The method for determining mechanical degradation of parts of a centrifugal pump according to claim 2 comprising calculating a theoretical efficiency: ${?}_{\mathrm{theoretical}}=\frac{?.Math.g.Math.{\mathrm{Hp}}_{\mathrm{th}}.Math.\mathrm{Qp}}{{\mathrm{Pw}}_{\mathrm{Qp}}}$ and calculating an impact of the Excessive wear-ring clearance on the overall pump as: ${?}_{\mathrm{WearRingImpact}}=\frac{{?}_{\mathrm{wearRing}}-{?}_{\mathrm{theoretical}}}{{?}_{\mathrm{theoretical}}}$

4. The method according to claim 1 wherein calculating an impeller wear impact comprises at iso-pump flow rate ?Q=0 calculating a mechanical efficiency: ${?}_m=\frac{P_I}{P_s}=\frac{?.Math.g.Math.{\mathrm{Hp}}_{\mathrm{th}}.Math.\left(Q_p+?Q\right)}{{\mathrm{Pw}}_{\mathrm{Qp}}}=\frac{?.Math.g.Math.{\mathrm{Hp}}_{\mathrm{th}}.Math.\mathrm{Qp}}{{\mathrm{Pw}}_{\mathrm{Qp}}}$ and calculating the efficiency of the pump with impeller wear impact ${?}_{\mathrm{impellerWear}}={?}_m?{?}_{\mathrm{HY}}?{?}_v=\frac{?.Math.g.Math.\left({\mathrm{Hp}}_{\mathrm{th}}-\left({\mathrm{Hp}}_{\mathrm{pwp}}-\mathrm{Hp}\right)\right).Math.\mathrm{Qp}}{{\mathrm{Pw}}_{\mathrm{Qp}}}\mathrm{where}{?}_{\mathrm{HY}}=\frac{\left({\mathrm{Hp}}_{\mathrm{th}}-\left({\mathrm{Hp}}_{\mathrm{pwp}}-\mathrm{Hp}\right)\right)}{{\mathrm{Hp}}_{\mathrm{th}}}$ and a volumetric efficiency ?.sub.v is set to 1.

5. The method for determining mechanical degradation of parts of a centrifugal pump according to claim 4 comprising calculating the impact of the impeller wear on the overall pump wear as: ${?}_{\mathrm{ImpellerWearImpact}}=\frac{{?}_{\mathrm{impellerWear}}-{?}_{\mathrm{theoretical}}}{{?}_{\mathrm{theoretical}}}\mathrm{where}{?}_{\mathrm{theoretical}}=\frac{?.Math.g.Math.{\mathrm{Hp}}_{\mathrm{th}}.Math.Q_p}{{\mathrm{Pw}}_{\mathrm{Qp}}}$

6. The method for determining mechanical degradation of parts of a centrifugal pump according to claim 1 repeated from time to time to obtain a plurality of measurements of the global efficiency of the pump.

7. The method for determining mechanical degradation of parts of a centrifugal pump according to claim 6 comprising a program designed to detect an evolution of a pump wear-ring clearance evolution through calculating said wear-ring clearance effect through measuring the initial power and flow rate of the pump at a time t0, calculating the initial Head of the pump Hp.sub.Pwp, calculating the initial loss of Head (Hp.sub.th?Hp.sub.Pwp).sub.t0, measuring from time to time t.sub.n=t.sub.n?1+?t with the pump in use the power and flow rate of the pump and calculating the head and loss of Head due to the wear-ring clearance, comparing the obtained wear-ring clearance effect (Hp.sub.th?Hp.sub.Pwp).sub.tn at time t.sub.n with the initial Head loss at time t0 to obtain a wear-ring clearance evolution of the pump.

8. The method for determining mechanical degradation of parts of a centrifugal pump according to claim 6 comprising identifying with said program an evolution of a pump impeller wear evolution through calculating said impeller wear effect through measuring an initial input pressure p.sub.int0, an actual output pressure p.sub.outt0 and an initial pump power Pwp.sub.t0 of the pump at a time t0, calculating the initial Head of the pump Hp.sub.Pwp at iso-pump flow rate ?Q=0, calculating the initial loss of Head (Hp.sub.Pwp?Hp).sub.t0, measuring from time to time t.sub.nt.sub.n?1+?t with the pump in use the input pressure p.sub.intn, Output pressure p.sub.outtn and pump power Pwp.sub.tn of the pump and calculating the head and loss of Head due to the impeller wear at iso-pump flow rate ?Q=0, comparing the obtained impeller wear (Hp.sub.Pwp?Hp).sub.tn with the initial Head loss to obtain a impeller wear evolution of the pump.

9. The method for determining mechanical degradation of parts of a centrifugal pump according to claim 1 wherein said measurements are done in real time during operation of the pump.

10. The method for determining degradation of a centrifugal pump according to claim 1 comprising comparing of an actual flow rate with at least one customer defined flow rate lower limit and providing a warning signal in case of detection of a flow rate lower than said lower limit.

11. The method for determining degradation of a centrifugal pump according to claim 10 comprising calculating the impact of the degradation on the efficiency of said impeller and provision of ageing data comprising flow rate reduction and/or head reduction.

12. The method for determining degradation of a centrifugal pump according to claim 11 comprising calculating the impact of such degradation on the energy consumption of the pump.

13. The method for determining degradation of a centrifugal pump according to claim 1 comprising creating warning signals upon detection of defined wear-ring clearance and/or impeller wear for providing data for predictive maintenance.

14. The method for determining degradation of a centrifugal pump according to claim 1 comprising entering said theoretical Pump mechanical Power versus Flow rate curve, said theoretical Head versus Flow rate curve from the pump manufacturer as initial theoretical pump data in a calculation program.

15. A non-transitory computer-readable recording medium on which a software is stored to implement the method according to claim 1 when the software is executed by a processor.

16. A non-transitory computer-readable recording medium on which computer software is stored, the computer software comprising instructions to implement the method according to claim 2 when the software is executed by a processor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] A detailed description of exemplary embodiments of the invention will be discussed hereunder in reference to the attached drawings where:

[0044] FIG. 1: shows a side cut view of a centrifugal pump;

[0045] FIG. 2A: shows a Pump Mechanical Power versus Pump Flow Rate curve for a new and a damaged pump;

[0046] FIG. 2B: shows a Pump Head versus Pump flow rate curve for a new and a damaged pump;

[0047] FIG. 3: shows degradation curves of a pump during part of its life;

[0048] FIG. 4: shows a simplified flowchart of a first measurement of the disclosure;

[0049] FIG. 5: shows a simplified flowchart of a second measurement of the disclosure;

[0050] FIGS. 6A and 6B: shows a simplified flowcharts of other calculations of the disclosure;

[0051] FIG. 7: shows a simplified flowchart of a first method of measuring evolution of a pump according to the disclosure;

[0052] FIG. 8: shows a simplified flowchart of a second method of measuring evolution of a pump according to the disclosure;

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0053] The present invention concerns a method for identifying the impact of an impeller wear and excessive wear-ring clearance on the whole performance of a centrifugal pump such as shown in FIG. 1 having a body 1, an impeller 2 with impeller blades 3 and impeller axis 4.

[0054] Centrifugal pumps are working in different hydraulic applications, from clean water to wastewater applications. It transports different kinds of fluid with different properties and densities. During their operation, the different mechanical parts (impeller, blades, wear-ring, diffuser . . . ) that compose a centrifugal pump suffer, and they can wear differently depending on the causes: cavitation, corrosion, abrasion, abnormal usage . . . ; The degradation of those parts generates internal losses and decreases the performance of such pumps. The losses can be quantified in terms of flow rate and losses in terms of pump total dynamic head capacity.

[0055] Three major losses inside a centrifugal pump are considered: [0056] Friction losses [0057] Shock losses [0058] Leakage losses

[0059] The leakage losses are associated with an excessive wear-ring clearance that is the wear of the blades tips and wear-ring which causes an excessive clearance 5 inside the carter of the pump. Such excessive clearance increases the flow rate recirculating between the rotating and stationary parts of the pump stage. Because of such clearance, the pump is rejecting a flow rate quantity lower than what has been stirred inside the pump. The flow rate inside the pump is higher than what can be measured in the discharge line of the pump.

[0060] Friction losses and shock losses are associated with the wear of the impeller and diffuser because they mainly participate in decreasing of the pump head at a same pumped flow due to losses by friction on the walls of the blades 3 and by shock due to the modification of angles of attack of worn blades.

[0061] Friction loss is prominent at high flow rates. In contrast, leakage loss is more present at relatively low flow rates. Shock loss takes place when the liquid flow rate differs from the designed flow rate.

[0062] The objective of the present disclosure is to provide a method to identify the impact of both the impeller wear and the excessive wear-ring clearance on the overall performance of a centrifugal pump having a fluid inlet A, an impeller 2 and a fluid outlet B.

[0063] The first law of thermodynamics provides

[00012]$P_s=\stackrel{?}{m}\left[{\left(h+\frac{V^2}{2}+{\mathrm{gZ}}_e\right)}_{\mathrm{out}}-{\left(h+\frac{V^2}{2}+{\mathrm{gZ}}_e\right)}_{\mathrm{in}}\right]$$\mathrm{with}$$h=u+\frac{p}{?}$ [0064] in which: [0065] Ps is the motor shaft power [0066] {dot over (m)} is the mass flow rate (kg/s) [0067] u is the internal energy (kcal/kg multiplied by J.Math.m.sup.2/s.sup.2) [0068] p is the static pressure (Pa=N/m.sup.2) [0069] ? is the fluid mass density [0070] V is the absolute velocity of fluid (m/s) [0071] g is the acceleration due to gravity (9.80665 m/s.sup.2) [0072] Ze is the elevation height at the point of interest (m)

[0073] The shaft power is commonly expressed in terms of Head and mass flow rate as in the following equation:

[00013]$\frac{P_s}{\stackrel{?}{m}}=g?H+?u$$H=\frac{p}{?g}+\frac{V^2}{2g}+Z_e$

where ?H is the Head across the pump (m)

[0074] The change in H is called the Head ?H of the pump; and because H includes the velocity head V.sup.2/2 g and the elevation head Ze at the point of interest, ?H is often called the total dynamic head. ?H is often abbreviated to simply H and is the increase in height of a column of liquid that the pump would create if the static pressure head p/?g and the velocity head V.sup.2/2 g were converted without loss into elevation head Ze their respective locations at the inlet A to and outlet B from the control volume.

[0075] Not all the mechanical input energy per unit mass ends up as useful pump output energy per unit mass g?H. This is expressed by:

[00014]$\frac{P_s}{\stackrel{?}{m}}>g?H$$\mathrm{or}$$?<1$

[0076] The overall pump efficiency ? is expressed by the following equation:

[00015]$?=\frac{g?H\stackrel{?}{m}}{P_s}$

[0077] The mass flow rate m can be expressed by:

[00016]$\stackrel{?}{m}=?Q$

Where:

[0078] Q is the flow rate (m.sup.3/s).

[0079] Then:

[00017]$?=\frac{P_I}{P_s}?\frac{g?H\left(\stackrel{?}{m}+{\stackrel{?}{m}}_{\mathrm{Le}}\right)}{P_I}?\frac{\stackrel{?}{m}}{\left(\stackrel{?}{m}+{\stackrel{?}{m}}_L\right)}$

Where:

[0080] [00018]$P_1=g?H_{\mathrm{th}}\left(\stackrel{?}{m}+{\stackrel{?}{m}}_{\mathrm{Le}}\right)$

In which H.sub.th is the theoretical Head without losses inside the pump,
and Le are the leakages which provides:

[00019]$?=\frac{P_I}{P_s}?\frac{?H}{?H_{\mathrm{th}}}?\frac{Q}{\left(Q+Q_L\right)}={?}_m?{?}_{\mathrm{HY}}?{?}_v$

[0081] The mechanical efficiency is defined as:

[00020]${?}_m=\frac{P_I}{P_s}=\frac{P_s-P_D}{P_s}$

[0082] The hydraulic efficiency is defined as:

[00021]${?}_{\mathrm{HY}}=\frac{?H}{?H_{\mathrm{th}}}=\frac{?H_i-.Math.H_L}{?H_{\mathrm{th}}}$

where the initial head Hi is the theoretical head H.sub.th and where H.sub.L corresponds to losses,

[0083] The volumetric efficiency is defined as:

[00022]${?}_v=\frac{Q}{\left(Q+Q_{\mathrm{Le}}\right)}$

[0084] The theoretical head is defined by the following equation:

[00023]$H_{\mathrm{th}}=\frac{{\left(2?R_2\right)}^2}{g}?N^2+\frac{2?R_2}{g{S}_2}?\frac{\cos \left({?}_2\right)}{.Math.\sin \left({?}_2\right).Math.}?N?q_v$

[0085] An equation that defines wear of a pump is:

[00024]$H_r=H_{\mathrm{th}}-H_{\mathrm{friction}}-H_{\mathrm{Shock}}-H_{Le\mathrm{akage}}-H_{\mathrm{recirculation}}-H_{\mathrm{diffuser}}-H_{\mathrm{disk}}$

[0086] Pump manufacturers provide pump curve datasheets which are already considering initial losses of a pump due to friction, shock, and leakage inside the pump as manufactured. As known in the art, the pump curves are different from the Euler theoretical head curve. In the present disclosure, the initial status of the pump as in the datasheet becomes the theoretical characteristic of the pump on which calculations are based. The evolution of the pump curve starting from the datasheet corresponds to an evolution of the internal mechanical parts of the pump.

[0087] The present disclosure provides an identification of the impact of the impeller wear and excessive wear-ring clearance on the whole pump performance. A purpose of the present disclosure is to detect the evolution of both mechanical parts inside the pump and how they impact the performance and energy consumption of the pump. The proposed method is based on a model of efficiency and a method to separate impeller wear and excessive wear-ring clearance based on Mechanical Power versus Flow Rate curves such as in FIG. 2A which shows an actual pump curve 12 in dotted line and a theoretical or manufacturer curve 13 in solid line and based on Pump Head versus Flow Rate curves such as in FIG. 2B which shows an actual pump curve 14 in dotted lines and a theoretical or manufacturer curve 15 in solid line.

[0088] Considering an operating point measured on an example of installation in use for pumping water in which a Pump flow rate is for example 15 m3/h, a Pump Head: 46 m, a Pump Mechanical power: 4.18 kW. A wear-ring clearance impact can be seen on the characteristic Pump mechanical power vs. Flow rate of FIG. 2A where, at the operating point 121 having a pump flow rate Qp, and a measured power Pwp, such power Pwp is higher than the theoretical power Pw.sub.Qp on the theoretical Mechanical Power versus Pump Flow rate curve 13 corresponding to Qp at point 131. In such curve, Qp.sub.Pwp is the projection of the measured power on the theoretical Mechanical Power versus Pump Flow rate curve 13 at point 132 allowing calculate the flow rate that the pump sees internally including the internal recirculation due to wear-ring clearance. Pw.sub.Qp is the projection of the measured flow rate 121 on the theoretical Mechanical Power versus Pump Flow rate curve 13 and corresponds to the mechanical power that should be given if the pump behaves as given by the pump manufacturer. It should be noted that the actual pump curve 12 is shown for a better understanding of the phenomenon but only the current working point Qp, Pwp is needed for the calculation. With a projection of theses operating points on the characteristics Pump Head versus Pump flow rate in FIG. 2B where the theoretical curve 15 is the solid line and the actual pump curve 14 is the dotted line for reference, it can be observed that the impact of the internal re-circulation in the pump implies a drop of the pump head Hp.sub.Pwp at point 142 from the theoretical pump head Hp.sub.th that should be obtained at the measured flow rate Qp at point 151. This provides the impact of the wear-ring clearance on the pump head because the pump doesn't see the flow rate measured externally but the flow rate inside the pump which is higher than measured:

[00025]$Q_{p_{\mathrm{pump}}}=Q_{p_{\mathrm{Meas}}}+?Q$$\mathrm{Where}:$$Q_{p_{\mathrm{pump}}}=Q{P}_{\mathrm{Pwp}}$$Q_{p_{\mathrm{Meas}}}=Q_p$

[0089] ?Q is the additional flow rate due to the increasing of the wear-ring clearance compared to initial status of the pump that is provided by the Manufacturer.

[0090] To identify the impact of the wear-ring clearance on the overall efficiency of the pump, it can be considered that for the same pump head Hp.sub.Pwp corresponding to the measured power, there is, according to FIG. 2B, a point at (Qp, HP.sub.Pwp) and a point at (Qp.sub.Pwp, Hp.sub.Pwp). Then, because at Iso-Pump Head: ?H.sub.L=0, the Head H=H.sub.th=Hp.sub.Pwp. In consequence, the measures necessary to determine the wear-ring clearance impact in such case are flow rate and mechanical power.

[0091] The method to determine the wear-ring clearance effect shown on the flowchart of FIG. 4 uses: [0092] measuring 200 an actual pump flow rate Qp and actual pump power Pwp 121, [0093] calculating 210 an internal flow rate of the pump Qp.sub.Pwp 132 through projecting said actual pump power Pwp on a theoretical Pump Mechanical power versus Pump Flow rate curve (13) at iso mechanical power, [0094] calculating 220 the mechanical power Pw.sub.Qp 131 that should be present if the pump works as specified in the theoretical curve through projecting said actual pump flow rate on said theoretical Pump Mechanical Power versus Pump Flow rate curve 13 at iso flow rate, [0095] applying 230 the measured flow rate Qp on a theoretical Pump Head versus Pump Flow rate curve 15 to obtain a theoretical Head Hp.sub.th 151, [0096] applying 240 the internal flow rate of the pump Qp.sub.Pwp on said theoretical Pump Head versus Pump Flow rate curve 15 to obtain an internal Head Hp.sub.Pwp 152, [0097] calculating 250 a difference between said theoretical Head and said internal Head Hp.sub.th?Hp.sub.Pwp to obtain the loss of Head due to the wear-ring clearance.

[0098] In FIG. 6A is a method that comprises calculating 400 a flow rate inside the pump

[00026]$Q_{p_{\mathrm{pump}}}=Q{p}_{\mathrm{Pwp}}=Qp+?Q,$

[0099] Where ?Q is the additional flow rate due to the increasing of the wear-ring clearance compared to the initial status of the pump that is provided by the theoretical Pump Head versus Flow rate curve 15. Considering that at the pump head Hp.sub.Pwp corresponding to the measured power and at iso-Pump Head H=H.sub.th=Hp.sub.Pwp the Hydraulic efficiency being equal to 1, the method comprises setting 405 a hydraulic efficiency at:

[00027]${?}_{\mathrm{HY}}=\frac{H}{H_{\mathrm{th}}}=1,$

[0100] And comprises calculating 410 a mechanical efficiency.

[00028]${?}_m=\frac{P_I}{P_s}=\frac{?.g.{\mathrm{Hp}}_{\mathrm{Pwp}}\left(Q_p+?Q\right)}{{\mathrm{Pw}}_p}$

[0101] Still considering the hydraulic efficiency:

[00029]${?}_{\mathrm{HY}}=\frac{H}{H_{\mathrm{th}}}=1$

at step 405

[0102] and the mechanical efficiency.

[00030]${?}_m=\frac{P_I}{P_s}=\frac{?.g.{\mathrm{Hp}}_{\mathrm{Pwp}}\left(Q_p+?Q\right)}{{\mathrm{Pw}}_p}$

[0103] at step 410 with the volumetric efficiency transformed in:

[00031]${?}_v=\frac{Q_p}{\left(Q_p+?Q\right)}$

at step 420 allows to define the efficiency due only to pump wear-ring clearance impact:

[00032]${?}_{\mathrm{wearRing}}={?}_m?{?}_{\mathrm{HY}}?{?}_v=\frac{?.g.{\mathrm{Hp}}_{\mathrm{Pwp}}.Math.Q_p}{{\mathrm{Pw}}_p}$

[0104] The impact of the Excessive wear-ring clearance on the overall pump wear is then calculated at 450 as:

[00033]${?}_{\mathrm{WearRingImpact}}=\frac{{?}_{\mathrm{wearRing}}-{?}_{\mathrm{theoretical}}}{{?}_{\mathrm{theoretical}}}$

Where

[0105] [00034]${?}_{\mathrm{theoretical}}=\frac{?.g.{\mathrm{Hp}}_{\mathrm{th}}.Math.Q_p}{P{w}_{\mathrm{Qp}}}$

is introduced at 440.

[0106] This permits to remove the part of pump head from the theoretical pump head at a flow rate value Qp that has been changed due to the increasing of wear-ring clearance.

[0107] Identification of the impact of impeller wear on the characteristic is possible with measurements of pressure upstream and downstream of the pump to get the pump head Hp and mechanical power measurement since such impact is only dependent on the head losses from frictions and shocks on the blades.

[0108] The method for calculating said impeller wear effect is shown in FIG. 5 and done through: [0109] measuring 300 an actual input pressure p.sub.in, an actual output pressure p.sub.out and an actual pump power Pwp, [0110] calculating 310 a theoretical flow rate Qp.sub.Pwp corresponding to the measured mechanical power Pwp 132 on a theoretical pump characteristic Pump Power versus Pump Flow rate curve 13,

[0111] Projecting 320 such theoretical flow rate Qp.sub.Pwp 152 on a theoretical Pump Head versus Pump Flow rate curve 15 at iso-pump flow rate ?Q=0 to obtain a theoretical Pump Head Hp.sub.Pwp, [0112] calculating 330 the actual Pump Head Hp from the actual input pressure p.sub.in, and the actual output pressure p.sub.out and a pumped fluid density as known in the art, [0113] calculating 340 the loss of head due to the impeller wear as Hp.sub.Pwp?Hp.

[0114] At Iso-Pump Flow axis, the volumetric efficiency may be expressed as shown by the following formula:

[00035]${?}_v=1$ [0115] because at iso-flow, there is no consideration of ?Q, the volumetric efficiency is equal to 1.

[0116] The measured mechanical power Pwp is projected on the theoretical Mechanical Pump Power versus Pump Flow rate curve 13 to obtain a theoretical pump flow rate Qp.sub.Pwp corresponding to such mechanical power Pwp. Then, the theoretical Pump Flow rate is used to obtain a theoretical Head Hp.sub.Pwp which after calculation of the current Head Hp with the input and output pressures allows to express the hydraulic efficiency by:

[00036]${?}_{\mathrm{HY}}=\frac{{\mathrm{Hp}}_{\mathrm{th}}-\left({\mathrm{Hp}}_{\mathrm{pwp}}-\mathrm{Hp}\right)}{{\mathrm{Hp}}_{\mathrm{th}}}$

[0117] The mechanical efficiency at iso-flow ?Q=0 allowing to calculate in 470:

[00037]${?}_m=\frac{P_I}{P_S}=\frac{?.Math.g.Math.{\mathrm{Hp}}_{\mathrm{th}}\left(Q_p+?Q\right)}{{\mathrm{Pw}}_{\mathrm{Qp}}}=\frac{?.Math.g.Math.{\mathrm{Hp}}_{\mathrm{th}}.Math.Q_p}{{\mathrm{Pw}}_{\mathrm{Qp}}}$

[0118] Which allows to define in 480 the loss of efficiency due only to pump wear-ring clearance:

[00038]${?}_{\mathrm{impellerWear}}={?}_m?{?}_{\mathrm{HY}}?{?}_v=\frac{?.Math.g.Math.\left({\mathrm{Hp}}_{\mathrm{th}}-\left({\mathrm{Hp}}_{\mathrm{pwp}}-\mathrm{Hp}\right)\right).Math.Q_p}{{\mathrm{Pw}}_{\mathrm{Qp}}}$ [0119] considering in 475 that ?.sub.v=1, the impact of the impeller wear on the overall pump wear is then given by:

[00039]${?}_{\mathrm{ImpellerWearImpact}}=\frac{{?}_{\mathrm{impellerWear}}-{?}_{\mathrm{theoretical}}}{{?}_{\mathrm{theoretical}}}\mathrm{Where}{?}_{\mathrm{theoretical}}=\frac{?.Math.g.Math.{\mathrm{Hp}}_{\mathrm{th}}.Math.Q_p}{{\mathrm{Pw}}_{\mathrm{Qp}}}\mathrm{in}\mathrm{step}490.$

[0120] All these calculated data may be displayed on a monitoring computer or memorized to provide tracking of the degradation of the pump in order to provide information as per the risk of failure in predictive maintenance programs.

[0121] This allows to identify a fault related to both impeller wear or/and excessive wear-ring clearance to a predefined threshold (based on the norm: Pump Detection Tolerances ISO9906).

[0122] The method of calculating the wear data may be repeated from time to time to obtain a plurality of measurements of the global efficiency of the pump during its working life.

[0123] A program designed to detect an evolution of a pump wear-ring clearance evolution such as shown in FIG. 7 may calculate said wear-ring clearance effect through measuring the initial power and flow rate of the pump at a time to step 500, calculating 510 the initial Head of the pump Hp.sub.Pwp, calculating 520 the initial loss of Head (Hp.sub.th?Hp.sub.Pwp).sub.t0 as an initialization phase. Then the program may measure from time to time t.sub.n=t.sub.n?1+?t 570, e.g. every day or week or at dedicated times within the life of the pump, with the pump in use the power and flow rate of the pump and calculate the head 530 and loss of Head 540 due to the wear-ring clearance, comparing 550 the obtained wear-ring clearance effect (Hp.sub.th?Hp.sub.Pwp)t.sub.n with the initial Head loss to obtain a wear-ring clearance evolution 560 of the pump.

[0124] Again, this can be done periodically, and the values displayed and/or memorized to draw wear curves of the pump.

[0125] The program as depicted in FIG. 8 may also survey an evolution of a pump impeller wear evolution through calculating said impeller wear effect through measuring an initial input pressure pinto, an actual output pressure p.sub.outt0 and an initial pump power Pwp.sub.t0 of the pump at a time t0 600 as an initialization. Then during life of the pump similarly, the program may calculate 610 the initial Head of the pump Hp.sub.Pwp at iso-pump flow rate ?Q=0, calculate 620 the initial loss of Head (Hp.sub.Pwp?Hp).sub.t0, measuring from time to time t.sub.n=t.sub.n?1+?t at 670 with a volumetric efficiency set to 1 in step 675 with the pump in use the input pressure p.sub.intn, output pressure p.sub.outtn and pump power Pwp.sub.tn of the pump and calculate the head 630 and loss of Head 640 due to the impeller wear at iso-pump flow rate ?Q=0, compare 650 the obtained impeller wear (Hp.sub.Pwp?Hp)t.sub.n with the initial Head loss to obtain a impeller wear evolution 660 of the pump.

[0126] The calculations of FIGS. 6A and 6B may also be done at each iteration of the two program parts shown in FIGS. 7 and 8 and discussed above embedding the programs of FIGS. 4 and 5, the measurements and calculation being preferably done in real time during operation of the pump.

[0127] It should be noted again that the actual curve Pump Mechanical Power versus Pump Flow rate 12 in FIG. 2A and the curve Pump Head versus Pump Flow rate 14 in FIG. 2B are not calculated and are shown for understanding the wear phenomena since only a working point with (Qp, Pwp) values is needed to obtain the wear-ring clearance effect and only a working point with (Hp, Pwp) values is needed to obtain the impeller wear effect at a moment in the life of the pump. The measurements and calculations provided permit to identify the impact of each part (impeller wear and wear-ring clearance) on the overall pump wear for all pump operating points as in FIG. 3 where curve 16 provides the percentage of performance degradation due to excessive wear-ring clearance, curve 17 shows the percentage of performance degradation due to impeller wear and curve 18 corresponds to the percentage of performance degradation due to both excessive wear-ring clearance and impeller wear.

[0128] The present disclosure provides means to identify if there is a fault related to impeller wear or wear-ring clearance separately and to identify the impact of each fault on the pump wear and performances.

[0129] Take the advantage of pump efficiency analysis to identify the problems on the mechanical part and their status.

[0130] In order to provide the theoretical curves in the program that implements the method of the present disclosure, the pump curves from the manufacturer are entered in such program in a preliminary step as such theoretical pump curves.

[0131] An identification of an evolution of the wear ring clearance is done by regularly analyzing the measurements (Power, flow rate) and calculating the wear ring clearance effect using the theoretical pump curves and calculating the mechanical efficiency, hydraulic efficiency, and volumetric efficiency to get the global efficiency at different moments of the life of the pump and to compare later values of such efficiencies with older values with the new status of wear-ring clearance.

[0132] The method also provides an identification of the evolution of the impeller wear after deducing the impact of the wear-ring clearance from the theoretical pump curve by analyzing the measurement (Power, Pump head) and the pump curve at flow rate-axis and computing the mechanical efficiency, hydraulic efficiency, and volumetric efficiency to get the global efficiency with the new status of the impeller.

[0133] The method may also comprise comparing of an actual flow rate with at least one customer defined flow rate lower limit and providing a warning signal in case of detection of a flow rate lower than said lower limit, a calculation of the impact of the degradation on the efficiency of said impeller and provision of ageing data comprising flow rate reduction and/or head reduction, a calculation of the impact of such degradation on the energy consumption of the pump.

[0134] A survey method may comprise also a program to create warning signals upon detection of defined wear-ring clearance and/or impeller wear for providing data for predictive maintenance.

[0135] An initialization method may also comprise entering said theoretical Pump mechanical Power versus Flow rate curve 13, said theoretical Head versus Flow rate curve 15 from the pump manufacturer as initial theoretical pump data in a calculation program executing the method of the disclosure.

[0136] The invention is not limited to the above description and in example, the program may be embedded in a control unit of the pump connected to sensors on the pump to get the measurement values or embedded in a remote-control center.