JNE 313 Advanced Engineering Knowledge: Sludge Pump Suction Loss

This report addresses the critical issue of sludge pump loss of suction in marine engineering, a problem that leads to decreased pump performance and potential equipment failure. The report details the function of sludge pumps, which are designed to handle fluids with high solid content, and the various causes of suction loss, including vaporization, vane passing syndrome, and inadequate Net Positive Suction Head (NPSH). It explains how loss of suction leads to the formation of bubbles, which then collapse, causing shockwaves that damage the impeller and lead to vibration. The report also provides solutions, such as understanding NPSH requirements during pump design, and discusses the adverse effects of suction loss, including reduced efficiency and damage to pump components. The report concludes by summarizing the key issues and reinforcing the importance of understanding and addressing suction loss to ensure the reliable operation of marine sludge pumps.

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Marine Engineering - General
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SLUDGE PUMP LOSS OF SUCTION
Table of Contents
Executive summary.........................................................................................................................2
Introduction......................................................................................................................................2
Causes if loss of suction..................................................................................................................3
How to solve the loss of suction in a sludge pump..........................................................................4
Effects of loss of suction in the sludge pump..................................................................................5
Conclusion.......................................................................................................................................6
References........................................................................................................................................6

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Executive summary
The main purpose of the sludge pump is to pump the fluid wastes which have very high amount
of solid content. Marine sludge pump is also referred to as a marine slurry pump, marine residue
pump or marine mud pump. The general application of the on board vessels or ship marine
sledges is for the residue from the purifies after the lube and the fuel have been purified, The
dirty or the sludge is normally stored in a tank. The wasters are removed when thank is full.
Loss of suction in sludge pump occurs due changing of liquid to vapour and creating a very high
pressure and temperature. When the sludge pump losses suction, bubbles usually forms. As the
pressure in Sludge pump increases, the bubbles which were initially formed collapses in the form
of an implosion, which is equal to an explosion. The collapse of the bubbles causes shockwaves
to move through the liquid and hit the impeller which causes serious mechanical damage.
Vibration is one of common sign of loss of suction in the sludge pump, and mostly the first
symptoms of an issue.
Introduction
Marine sludge pump is also referred to as a marine slurry pump, marine residue pump or marine
mud pump. Marine sludge pump is designed to transferring wastes fluids containing high amount
of solid content. Generally the marine sludge pump is a positive displacement pump. It facilitates
the handling of viscous, abrasive and heavy liquids which includes sewage, mud and wastes
(Nordberg, et al 2012). The marine sludge pump is usually progressive cavity pump i.e. marine

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air operated double diaphragm pump. In some scenarios, a gear oil pump can also be used in
handling marine oil sludge.
The general application of the on board vessels or ship marine sledges is for the residue from
the purifies after the lube and the fuel have been purified, The dirty or the sludge is normally
stored in a tank. The wasters are removed when thank is full (Hancock, 2015). .
Causes if loss of suction
Loss of suction occurs in the marine sludge pump when the pressure and temperature of the
liquid at the suction of the impeller equals to the vapour pressure. This phenomena can occur at
normal operating temperatures and low pressure (. Normally, it results in the liquid changing to
vapour and creating a very high pressure and temperature. When the sludge pump losses suction,
bubbles usually forms. As the pressure in Sludge pump increases, the bubbles which were
initially formed collapses in the form of an implosion, which is equal to an explosion. The
collapse of the bubbles causes shockwaves to move through the liquid and hit the impeller which
causes serious mechanical damage (Adahan, 2012). The figure below, shows a damaged
impeller.
o The sludge pump tank vent partially freezes in cold weather
o Vaporization of the liquid that is caused by loss of the suction head or it can be caused by
an increase in the suction temperature.
o Loss of suction in the sludge pump can caused by ‘Vane passing syndrome’ which is
normally caused by too small impeller to cut water clearance.
o The loss of sludge can be caused by a too high suction specific speed number which is
likely to cause damage to the internal recirculation challenges resulting to loss of suction.

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Fig 1: Damaged impeller (Pronk, et al 2015)
How to solve the loss of suction in a sludge pump
In the scenarios where there is no change in the suction conditions or the properties of the liquids
during the operations of the sludge pump, the loss of suction can be avoided easily during the
design of the pump. One of the key elements which need to be understood is the Net Positive
suction Head (NPSH) and one need also to take into this into account during the entire design
process. In simple terms, this is broken down as follows:

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o Net: is what is left when all the deductions have been made
o Positive is obvious
o Sanction head refers to the pressure at the pump inlet flange (Ratkovich et al 2013)
NPSH refers to the difference between the pressure which is available at the inlet of the pump
and the pressure of the liquid. Vapour pressure different for various liquids and the pressure and
temperature.
The pressure available in the inlet is usually what remains after the friction is lost, velocity head
loss and the outlet and the outlet losses been recognized within the suction pipework within the
pumping system. Because of this, during the designing process, it is very significant to establish
the losses and then process the unit losses (Hreiz, Latifi and Roche, 2015). Then perform the
deductions from the suction.
Effects of loss of suction in the sludge pump
Loss of suction causes a deterioration on the performance of the pump, vibrations and noise
which usually leads to failure of the sludge pump. Vibration is one of common sign of loss of
suction in the sludge pump, and mostly the first symptoms of an issue. The vibrations which
occurs as a result of loss of suction cause a lot of problems to the pump components such as
bearings, seal and shafts. The figures below shows the damaged elements as a result of loss of
suction.
Loss of suction has a great impact on the overall performance of the pump. Loss of suction
degrades the overall performance of the pump, which leads in the fluctuating flow rates and the
discharge pressure. Loss of suction also causes damages to the internal elements of the pump

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Fig 2: Hole in sludge pump impeller vane
Conclusion
In conclusion, Marine sludge pump is designed to transferring wastes fluids containing high
amount of solid content Generally the marine sludge pump is a positive displacement pump. It
facilitates the handling of viscous, abrasive and heavy liquids which includes sewage, mud and
wastes (Guyer, 2018). Loss of suction occurs in the marine sludge pump when the pressure and
temperature of the liquid at the suction of the impeller equals to the vapour pressure. This
phenomena can occur at normal operating temperatures and low pressure. Loss of suction
causes a deterioration on the performance of the pump, vibrations and noise which usually leads
to failure of the sludge pump. Vibration is one of common sig n of loss of suction in the sludge
pump, and mostly the first symptoms of an issue. The general application of the on board
vessels or ship marine sledges is for the residue from the purifies after the lube and the fuel
have been purified, The dirty or the sludge is normally stored in a tank (Roos, 2013).Other
causes of loss of suction in the sludge pumps includes: The sludge pump tank vent partially
freezes in cold weather. Vaporization of the liquid that is caused by loss of the suction head or
it can be caused by an increase in the suction temperature. Loss of suction in the sludge pump
can caused by ‘Vane passing syndrome’ which is normally caused by too small impeller to cut

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water clearance.The loss of sludge can be caused by a too high suction specific speed number
which is likely to cause damage to the internal recirculation challenges resulting to loss of
suction.

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References
Adahan, C. (2012). U.S. Patent No. 8,235,972. Washington, DC: U.S. Patent and Trademark
Office.
Guyer, J. P. (Ed.). (2018). An introduction to sludge handling, treatment and disposal. Guyer
Partners.
Hancock, J. C. (2015). U.S. Patent No. 9,108,230. Washington, DC: U.S. Patent and Trademark
Office.
Hreiz, R., Latifi, M. A., & Roche, N. (2015). Optimal design and operation of activated sludge
processes: State-of-the-art. Chemical Engineering Journal, 281, 900-920.
Nordberg, Å., Edström, M., Uusi-Penttilä, M., & Rasmuson, Å. C. (2012). Selective desorption
of carbon dioxide from sewage sludge for in-situ methane enrichment: Enrichment experiments
in pilot scale. Biomass and bioenergy, 37, 196-204.
Pronk, M., De Kreuk, M. K., De Bruin, B., Kamminga, P., Kleerebezem, R. V., & Van
Loosdrecht, M. C. M. (2015). Full scale performance of the aerobic granular sludge process for
sewage treatment. Water Research, 84, 207-217.
Ratkovich, N., Horn, W., Helmus, F. P., Rosenberger, S., Naessens, W., Nopens, I., & Bentzen,
T. R. (2013). Activated sludge rheology: a critical review on data collection and
modelling. Water research, 47(2), 463-482.
Roos, C. J. (2013). A guide to pumping manure slurries in centralized biogas digester systems.
Northwest CHP Application Center.