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Mission Magnum XP- 8x6x18 Centrifugal pump
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(Marine/Ocean)
(OP)
11 Aug 06 07:34 I have been commissioning a series of these pumps and have had overload problems with the drive motors on each, pumping test seawater. The pump curves supplied and the data sheets all check out ON PAPER. I suspect the data supplied by the contractor may be at fault. I have attempted to source the data and pump curves from the ORIGINAL Pump mfr's website , but it is not listed for this particular model. We are operating the pumps at rpm as on the data sheet. Our power supply is 400V 50 Hertz.
Would appreciate any one who has experience of these pumps supplying their findings. It is intended to use the pumps for drilling Mud at sg up to 2.0.
Replies continue below
(Mechanical)
11 Aug 06 07:58First question to ask when commisioning pumps and you have an overload situation - are they running in the right direction?if yes- you need to check flow and head - possibly the discharge head is a lot lower than specified and the pumps are running way-out on their curve.If they are overloading on seawater - you will have double the problem with the drilling mud at sg 2.
Naresuan University
Phitsanulok
Thailand
(Mechanical)
11 Aug 06 12:39The other potential problem that comes to mind for me is voltage to the motors. If your system is running lower voltage, the motors will draw higher amperage and could trip as a result. You should have an electrician verify the voltage with the pump running under load. If there is a resistance somewhere else in the system the voltage will drop and the amps will take you down.
I am not familar with the configuration of this pump model. If they are standard radial impellers, then high flow (as suggested by Artisi) could be the issue. If they are axial flow or mixed flow impellers, low flow is a potential concern.
Are you sure that your curves and data are for the installed impeller at the speed you are running? We have occasionally ordered pumps and had them tested in one configuration, but shipped in a different configuration. This is done if we have a planned rerate and want to test to the future condition. Perhaps the impellers are larger than the curve and data-sheet indicate.
(Marine/Ocean)
(OP)
11 Aug 06 15:56
I suspect the flowrate given on the data sheet is wrong. Unfortunately I do not have a flowmeter available , but I may overcome this by timing a flow into an adjacent tank. Rpm, pump direction are all ok, but Motor amps are way above FLA.
(Mechanical)
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13 Aug 06 15:49Chief,
If you want pump curves on the Magmum XP just the manufacturer or their local assistance office, which can be found on their website, and ask them for the pump curves of your model.
I do not know the exact requirements for the service intended for this pump. Has this pump for drilling mud to run to the end of curve? Many centrifugal pumps are not equipped with an electric motor of suitable size to allow end of curve operation. The data sheets supplied should detail the intended flow flow range and expected required head.
You do not indicate anything on the head and flow used in test, the intended head and flow on the data sheet and the operation point on the pump curve supplied, which makes it very difficult to understand to problem in detail.
The manufacturer could also give their opinion on the selected electric motor size and the intended operation range.
(Petroleum)
4 Dec 06 18:39With regards to Magnum XP pumps, I've been trying to get the Maintenance manual from National and Halco for over a week. Does anyone know whether the shaft thread is left or right hand thread. We have pumps that have been sitting for 2 years and we need to change impellers on them, unfortunately no manuals or information, and the impeller nose is solid, and I dont want to be forcing it against the thread. Any info would be greatly appreciated.
(Mechanical)
5 Dec 06 15:03I didn't know they made an 8x6-18.
Depending on how the pump and motor were sized, you might be having issues due to viscosity (or lack thereof).
(Mechanical)
6 Dec 06 08:01Drillmaint,
If the impeller is threaded on, it must be threaded so that it tightens with shaft rotation. If it turns clock wise, looking from the coupling toward the impeller, it is right hand thread. If it turns counter-clock-wise, it is left hand thread. If it is curved vanes on the impeller, imagine striking the end of the vane with a hammer. This would unscrew the impeller.
What is the configuration of this pump? I am not familiar with the model. Vertical, horizontal, single stage, multi-stage?
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The industrial pump is a slave to the pumping system. The system governs the pump. The system is composed of the suction and discharge vessels plus all pipes, elbows, valves, filters, fittings, and instrumentation. The pump reacts when the system changes.
If the pump is forced to do what it cannot do, then it fails frequently and prematurely. We call it mysterious pump failure, reactive maintenance, or unscheduled downtime. So, how do you know what your pump can do within the system?
The answer is simple, but not always realistic. The pump curve should be available and understood by everyone involved with the pump, although it rarely is.
You can get some good information off the pump and motor ID plates. The motor ID plate indicates the speed. The pump ID plate normally indicates the impeller diameter in inches.
With the pump speed and the impeller diameter, you can approach it in 2 ways.
At 1,800 RPM, the impeller diameter in inches, multiplied by itself, is the approximate shutoff head of the pump in feet. This means that a standard centrifugal pump with a six-inch impeller on a four-pole motor will generate 34 to 38 ft. of shutoff head (6 x 6 = 36).
Likewise, a nine-inch impeller on a four-pole motor would generate about 80 ft. of shutoff head (9 x 9 = 81). And a 13-inch impeller would generate about 170 ft. of shutoff head (13 x 13 = 169). These numbers are accurate within about 5 percent.
The best efficiency point (BEP) is about 85 percent of the shutoff head. The pump should be operated at, or close to, the best efficiency point.
The key word here is 'about.' This method has exceptions, depending on the pump design, application, and liquid. However, this covers about 90 percent of all centrifugal pumps. If the pump speed or impeller diameter changes, the pump performance varies by what are commonly referred to as the affinity laws.
The shutoff head is a simple concept. If you were to pump into a vertical pipe, the pump would push the liquid up into the pipe to a certain point beyond which no more elevation could be obtained. Flow becomes zero as all the energy of the electric motor is invested into maintaining elevation. This is the shutoff head.
Assuming you have a pump to fill a tank at 600 GPM with ambient water, the discharge pipe rises over the top of the tank and drops down into the tank.
When full, the level in the discharge vessel is 52 ft. above the level in the suction vessel. The system has two feet of friction losses with the pipe runs, the elbows, valves, and instrumentation.
The important elements of a typical centrifugal pump curve plotted on a graph. The vertical axis reads head or elevation in feet starting at 0. The horizontal axis reads flow in GPM starting at 0.
How would you specify a pump for this system? The pump must generate 54 ft. of head (52 ft. elevation change plus two feet friction losses) at 600 GPM. Your pump impeller diameter should be eight inches mated to a four-pole electric motor. The shutoff head would be approximately 64 ft. The BEP would be about 54 ft. (85 percent) at 600 GPM.
The BEP for a typical centrifugal pump is noted on the curve in the figure provided above with coordinates drawn to point C (best efficiency head in feet) and point D (best efficiency flow in GPM).
How would you know if this pump is performing as it should?
Ambient water at 54 ft. would convert into 23 PSI differential on the pump's pressure gauges. If the suction gauge reads zero PSI, the discharge gauge should read 23 PSI. A flowmeter might report a velocity that converts to 600 GPM. It's that easy. It also shows the importance of the instrumentation tech to pump reliability. Pumps need working gauges. Equipment operators need training to properly interpret them.
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