Centrifugal Pump Performance Curve Reading Method
Understanding of the pump performance curve is extremely necessary to choose a correct pump for the specified application. The pump performance curve consists of 4 set of curves.
- Head Vs Flow Curve.
- Brake Power Vs Flow Curve.
- Efficiency Vs Flow Curve.
- NPSHr Vs Flow Curve.
Centrifugal pump performance is drawn by multiple curves indicating either
- Various vane diameters at a continuing speed.
- Various speeds with a continuing vane diameter.
In this article, we’ll see solely varied vane diameters at a continuing speed.
Head Vs Flow Curve (H/Q)
In this curve, the pinnacle is on the vertical axis and flow on the horizontal axis. With a rise in pump flow, the pinnacle developed by the pump begins decreases.
The pump develops most head at zero flow it’s known as shutoff purpose or shutoff head and also the corresponding pressure is termed shutoff pressure. commonly the shutoff pressure is one.25 time of pump discharge pressure.
The line continues to the correct, with head reducing and flow increasing till the “end of the curve” is reached, (this is commonly outside the counseled operative vary of the pump).
Flow and head area unit joined, one can not be modified while not variable the opposite. the link between them is barred till wear or blockages amendment the pump characteristics.
Brake Power Vs Flow Curve (P/Q)
In this curve, the Break power is on the vertical axis and flow on the horizontal axis. As we tend to see from the curve, some braking power is needed at zero flow, this power is needed to beat the pump inertia and friction losses. From this curve, for the specified pump flow, the corresponding brake power is obtained.
Efficiency Vs Flow Curve (e/Q)
The potency curve is raising as a flow increase (refer figure). Then the curve reaches the most purpose and starts decreasing. the most purpose is termed Best potency Point(BEP).
If the pump runs at or almost about BEP, not solely we tend to get higher potency and conjointly the vibration of the pump is minimum.
NPSH(r) Vs Flow Curve(N/Q)
NPSH(r) price at pump rated purpose ought to be a minimum of 1m less that NPSH ‘available’. it’s known as the NPSH margin.
NPSHmargin = NPSH(a) – NPSH(r)
Normally NPSH check is disbursed once the NPSH’margin’ but one meter.
It is created from four to 5 points, every purpose being obtained from a separate NPSH check at a unique constant flow. this can be commonly disbursed once the preceding tests.
How to scan a pump Performance Curve
Now take into account a pump is needed to pump water from one vessel to a different vessel, the pump parameters area unit as follows
Rated Flow = 40m3/hr
Rated Head = 157 m
Liquid relative density = one
NPSH obtainable = 4m
1. Pump Rated Flow:
Point one, represent the rated flow(40m3/hr)of the pump.
2. Rated Head:
Point two represents the Rated head (157m). currently, the intersection section purpose of Rated Flow and Rated head within the vane curve is termed “Rated Impeller”. In our example the “Rated Impeller” diameter is 370mm.
3.Shut-off head:
The maximum head made by the pump at rated vane is termed “Shut off the head”. The corresponding pressure at the shut-off head is termed “Shut off Pressure”. The shut-off pressure is extremely necessary for pump downstream system style pressure. perpetually Downstream style pressure is bigger than Shut off Pressure for safe style.
Downstream style pressure > Shut off Pressure.
4.Minimum Continuous Stable Flow:
MCSF is that the minimum flow developed by the pump at rated vane. Below MSCF it’s not best to run the pump.
As a thumb rule, Minimum Continuous Stable Flow is twenty-fifths of “BEP Flow”.
5. Efficiency:
The rated flow of pump cross at the potency curve, the corresponding potency within the coordinate axis is termed pump “Rated Efficiency”. Refer “5a” within the curve drawn the rated potency.
As we tend to see the potency cure, from pump zero flow the curve starts rising and reaches the most purpose and begins decreasing with an increase in flow.
The maximum purpose of the potency curve is termed “Best potency purpose (BEP)”.Refer “5b” within the curve drawn the simplest potency purpose. The flow appreciates the BEP is termed “Best potency Flow”. The pump vibration level is low at BEP. it’s perpetually most popular to pick a pump whose rated flow is almost about Best potency Flow.
As per API 610, the rated flow shall be among the region of eighty to a hundred and tenth of BEP flow.Pumps shall have a most popular operative region of seventy you must a hundred and twenty you look after best potency flow (Refer figure it highlighted in “light blue color”)
6. Brake Power:
The brake power or rated power of the pump is the power needed to run the pump to deliver the rated flow at the rated head.
The rated flow of the pump cross at the Brake power curve and corresponding power within the coordinate axis is termed “Rated power of the pump” (Refer figure “6a”). For our example, the rated power is 35kW.
If the pump is needed {to begin|to start out|to begin} at open discharge valve or motor vehicle start condition. In such a case, the facility is needed for the pump, power appreciates the “End of the curve” of the brake power curve.
In view of the brake power required, engine kilowatt or hp will be chosen.
7. NPSH(r):
The appraised stream line cross with NPSH(r) bend and the relating NPSH(r) for the evaluated stream condition is acquired in the Y-hub. For our situation, the NPSH(r) is 2.5m.
NPSH edge (NPSH m) = NPSH(a) – NPSH(r)
Right now NPSH(a) is 4m.
NPSH edge = 4 – 2.5
NPSH edge = 1.5 m
Conclusion
As talked about, it would be ideal if you recollect the beneath referenced focuses to be check in divergent siphon execution bend for legitimate siphon determination
- Siphon Rated Flow
- Siphon Rated Head
- Appraised impeller Diameter
- Siphon BEP stream
- Stop head
- Proficiency
- Siphon appraised power
- Siphon End of Curve power
- NPSH required
- Favored Operation Range
- Permissible Operation Range
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