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Power Plant Centrifugal Pumps: Problem Analysis and Troubleshooting
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Monitoring The Centrifugal Pump – Mc Nally Institute
ABB Web feeds. Events Customer events Investor events Media events. Current share price. A sensor is used to determine the level or amount of fluids, liquids, or other substances that flow in an open or closed system called the level sensor. They are primarily known for measuring fuel levels, but they are also used in pumps that work with liquid materials. An ideal application for such a sensor would be to measure the number of liquid assets that are being pumped. This helps validate expectation and avoid fraud situations.
With the continued use of these sensors, any product manager can precisely see how much liquid is ready to be pumped and whether it should be stepped up. A magnetic sensor or "Hall Effect" sensor is a transducer, which varies its output voltage in reaction to a magnetic field.
These types of sensors are used for proximity switching, speed detection, positioning, and current sensing applications. In Centrifugal pumps, they can be used to detect structural wear on impeller blades of centrifugal pumps. Wear and tear of impeller blades lead to reduced pump efficiency and plant downtime. Using a magnetic circuit with the pump and its components, wear is estimated by measuring the gap between the impeller and the pump housing.
As the impeller wears, the gap between the impeller and the pump housing increases, causing the reluctance of the magnetic circuit to increase. In turn, it reduces the inductance of the coil driving the magnetic circuit. These are only some of the most popularly-used sensors with centrifugal pumps. However, the IIoT platform can be customized with required sensors to pick data that is most relevant to specific business operations. Sensors for the IIoT platform are the most affordable and efficient solution for predictive maintenance and real-time monitoring; as in most cases, they can be installed on existing pumps and do not require any pump modifications.
Over a million developers have joined DZone. Let's be friends:. IoT Sensors for Centrifugal Pumps. DZone 's Guide to. Want to learn more about how IoT sensors are transforming centrifugal pumps? Click here to learn more about IoT and pump operations. Free Resource. Like 4. Join the DZone community and get the full member experience. Join For Free. It helps to ensure optimal environment temperature at all times Pressure Sensors A pressure sensor is a device that senses pressure and converts it into an electric signal.
Water Quality Sensors If the pump deals in pumping water, such as in municipal water quality sensors, it will help to detect the water quality, chlorine residue, suspended solids, pH-level, and Ion monitoring among other requirements. Chemical Sensors Chemical sensors are ideal for centrifugal pumps used in the chemical industry. Further evidence in O ring hardening and setting may support this. The seal faces will also show signs of excessive wear and possible heat distress in the form of thermal cracking.
Cause: The most probable causes are dry running, flashing, or very poor face lubrication. Flashing being boiling of the fluid film on the seal faces. Other causes could be incorrect fitting of the seal causing high friction and thereby high temperatures within the seal or the pump is operating at excessive pressures or speed. Solution: Ensure seal does not run dry in the application. If this cannot be avoided a single seal with flush or a double seal with a barrier fluid should be considered ensuring proper lubrication of the seal.
Ensure the seal is properly installed as per seal manufacturers fitting instructions. An example of a mechanical seal where the seal faces have been allowed to run dry. O ring is deformed being axially moved from the fitted position close to the shaft step. Inspect the seal drive Mechanical seal designs all use some method to transmit torque from the shaft to the rotary seal face.
For the mechanical seals used on the LKH and SolidC centrifugal pumps this takes the form of a drive pin on the rotating part correctly engaging in the slot of the stationary part. Check the elastomer Swollen, sticky or disintegrating Cause: This is generally caused by chemical incompatibility with pumped media.
Solution: Replace with different elastomer material that is compatible from seal manufacturers recommendations. Usually the source of heat is the face or a metal to metal contact of two parts. Excessive face heat is caused by lack of lubrication and subsequent high friction. It could also be a sign that the pump has run dry. Replace with different elastomer material that is compatible from seal manufacturers recommendations.
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Compression set Cause: This is caused where the O ring has been unable to withstand the temperature of the pumped media - the O ring loses its roundness and becomes square in section. This may also occur if too much heat is generated at the seal faces. As the o ring extrudes it will tear in the gap between shaft and seal ring. Solution: Replace elastomer and reduce system pressures. Also check that the O ring groove size is correct by referring to seal manufacturer.
Cuts or nicks Cause: This is the most common failure and normally occurs during installation. Solution: By its nature elastomers slide on to the shafts with some interference and care should be taken when sliding new elastomers over any sharp edges, shoulders or old grub screw marks to avoid damage.
Lack of lubrication causes carbon to grind away. Seal drips steadily heavy leakage is normally from the faces rather than the o rings. Primary: Faces not flat. Faces cracked, chipped or blistered. Distortion of seal faces for thermal or mechanical reasons. Secondary: Seals nicked or scratched during installation. Leakage of fluid under pump shaft sleeve. O rings have been compression set hard and brittle.
O rings subjected to chemical attack soft and sticky. Incorrect seal materials specified. Ability to self-prime The Alfa Laval LKHSP self-priming centrifugal pump is specifically designed for pumping liquids containing air or gas without losing its pumping ability. The LKHSP self-priming pump can be used for emptying tanks, as CIP return pump and similar applications where there is a risk of air or gas mixing with the liquid in the suction line. During operation the water in the pump recirculates within the confines of the system with the ball valve open. The recirculation creates negative pressure which opens the non-return valve letting in fluid and air.
As the pump is now delivering fluid, the pressure increases and closes the ball valve.
The pump subsequently functions as a standard centrifugal pump. For satisfactory operation the static head on discharge line should be less than 8 metres. If the static head is higher than this figure, the spring in the ball valve between the tank and the inlet of the pump cannot open which will result in the pump being unable to prime. Rouging Rouging refers to a form of corrosion found in stainless steel. Rouging is a thin film, usually reddishbrown or golden in color, of iron oxide or hydroxide, typically on found on stainless steels. The contrast between this film and shiny metal accentuates this aesthetics problem.
The rouge film typically wipes off easily with a light cloth, but it reforms while the process fluid is in contact with the stainless steel. This problem is most chronic in the pharmaceutical industry on the interior surfaces of high purity water i. As stated, rouge is ferric oxide i. Particles of rust can become dislodged and be dispersed throughout a piping distribution system, often collecting on in-line filters. Stainless steel is stainless owing to the fact that the alloy forms a thin, protective, tenacious, transparent oxide film that protects it against destructive corrosive elements in aqueous solutions.
This film is composed of chromium oxide, and is said to make the steel passive against corrosion. Exposure to moist air will provide this passivation within a matter of minutes, and the film will thicken with time. The passive layer on the surface of stainless steels can breakdown by the interaction of ultra pure water, which is devoid of ionic elements, leading to rouging. The ionic pull of the water is strong enough to strip the protective chromium oxide off the steel surface.
This results in the stainless steel having to re-passivate by reforming another layer of chromium oxide film, which incorporates the rouge causing discoloration. During the brief time it takes to re-passivate, a thin layer of the stainless steel dissolves, or corrodes. The major elements composing stainless steel are iron, chromium and nickel. The chromium and nickel ions are soluble and go into the bulk solution. The iron, however, precipitates above a pH of 3 as iron hydroxide that readily oxidizes to ferric oxide, which is red in colour i.
In high purity water systems the rouge may be of three types: Class I Rouge originating from external sources, usually by erosion or cavitation of pump surfaces. Class II Rouge originating from chloride induced corrosion of the stainless steel surfaces.
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Class III Rouge, either blue or black, found in high temperature steam systems. Rouging can take place in pure water, ultra-pure water, steam, treated potable water or untreated process water. When designing a pumping system consideration should be given to the pipework, pump protection and operation. Have short straight inlet pipework. Avoid bends, tees and any restrictions close to either suction or discharge side of pump.
Use long radius bends wherever possible. Keep pipework horizontal where applicable. Include eccentric reducers on suction lines. Avoid the use of blind tees. Include for seal flushing pipework where applicable. All pipework must be supported. The pump must not be allowed to support any of the pipework weight. Protect the pump against blockage from hard solid objects e. Protect the pump from accidental operation against closed inlet and outlet valves.
Ensure pumped media is maintained at the correct temperature. Try to allow at least 0. Ensure fluid flow velocity is sufficient. Pre-start up Checks Before the pump unit is started it is important to ensure that pre-start up checks are made as follows:. Check that the pipework system has been purged to remove welding slag and any other debris. For purging purposes a bypass should be installed around the pump. Minimum recommended velocity 1. Fluid vaporising in suction line Air entering suction line Strainer or filter blocked Fluid viscosity above rated figure Fluid viscosity below rated figure Fluid temperature above rated figure Fluid temperature below rated figure.
Reverse motor Expel gas from suction line and pumping chamber and introduce fluid Increase suction line diameter. Increase suction head. Simplify suction line configuration and reduce length. Decrease fluid temperature - check effect of increased viscosity? Increase suction line diameter. Increase suction head or pressure on fluid surface, Simplify suction line configuration and reduce length. Remake pipework joints Service fittings Increase fluid temperature.
Increase motor speed.
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Check seal face viscosity limitations. Decrease fluid temperature Cool the pump casing. Reduce fluid temperature. Check seal face and elastomer temperature limitations. Heat the pump casing. Increase fluid temperature. Clean the system. Fit strainer to suction line. If solids cannot be eliminated, consider fitting double mechanical seals. Check for obstructions i. Service system and change to prevent problem recurring.
Simplify discharge line to decrease pressure. Increase flush flow rate. Check that flush fluid flows freely into seal area.