กฐA pump is just a component that will do exactly what it is designed to do. But if itกฏs not installed properly, then you can destroy it. Itกฏs a bit like Murphyกฏs Law: If something can go wrong, it will. And in the end, the ship owners will have to bear the costs.กฑ

A solid foundation

Solid pump foundations are at the top of our list. กฐIt is extremely important that these are done correctly. The foundation has to be supported so thereกฏs no chance of wobbling.กฑ In other words, do not install the pump on a soft plate จC a steel plate with no or missing support below. กฐThereกฏs an old shipyard saying: You need the same amount of steel below the plate as you have on top of it.กฑ

If the outfitting team wants to use weighted or spring-loaded supports, they must first check the design with DESMI or the steel engineer. กฐIt is not up to the individual outfitting team to decide. Most pumps today are vertical. And two-thirds of a pumpกฏs weight is actually the electrical motor. Some pumps are four and a half tons meaning the electrical motor is three tons. This all calls for very good foundations to avoid vibration, etc.กฑ

Pipes and valves

There are standard ISO rules for pipe routing, but these can be tricky to follow onboard a ship due to limited space. กฐSo that means you have to think a bit alternatively.กฑ On a ship, make sure that the pipe design allows the liquid flowing to the pump on the suction side at a maximum velocity of 1 meter per second (m/s). This is a rule of thumb so that you avoid creating water vortex or cavitation that will eventually destroy the pump.

And then there are valve choices. On ships, a big number of valves are butterfly valves, mainly because this is an inexpensive valve type. But a butterfly valve only works in the pumping direction. This is why there are always a non-return valve in series with the butterfly on pumps pressure side. Otherwise, if pumps are working in parallel and one pump is dormant without installed non-return valve, the active pump will pump liquid to the other pump instead จC no matter butterfly valve open or closed.

Furthermore, it is important that the valves are full bore (full port). This means that when the valve is open, it has the same diameter as the pipe. Don't use valves that are slightly smaller in diameter than the pipe. This will create small vortexes inside the pipe and will eventually destroy the pipe and the valve.

Materials and corrosion

It is also important to plan carefully for the pump material used, depending on the liquid it is pumping and conditions around it. Material choices for pumps include bronze, nickel aluminum bronze (NiAIBz), gun metal, cast iron, cast steel, stainless steel 304, stainless steel 316, and duplex. กฐAll of these materials have each their own advantages and disadvantages. Itกฏs important to consider theseกฑ.

DESMI typically uses stainless steel 316 or duplex for alkaline or acidic liquids, for example. กฐBut you have to handle this material very carefully. You need to know what youกฏre doing. Otherwise they can corrode.กฑ

DESMI designs its seawater pumps typically of NiALBz for a designed sea water temperature of 32กใC. Sea Water temperature above that becomes much more corrosive. Likewise, cast iron is not a good choice for seawater pumps in warm areas. กฐIf youกฏre operating in Greenland, then a cast iron pump can last a long time, but not if youกฏre working in the tropics.กฑ

For low temperature freshwater pumps, the DESMI design is using cast iron housing and NiAlBz impellers, designed for a water temperature of 36กใC. กฐThe problem with fresh water on a ship is that you need additives to remove oxygen as to avoid corrosion/rust. But there are many different kinds of additives and some of these make the water very viscous, and as result water can be leaking everywhere. Another problem with additives is that these chemicals change waters pH values. This is also something that needs to be considered when selecting materials.กฑ

Be aware of the potential for galvanic corrosion (also called bimetallic corrosion) when considering materials. This is a phenomenon that occurs when two different materials are put together จC like copper and iron in salt water. Salt water will act as an electrolyte.  กฐIt's a slow killer - It takes a long time before you find out it is a problem.กฑ

กฑIt is the same principle as used for protection steel with zinc anodes.กฑ

In the case with copper and iron จC the iron will slowly move to the copper.

กฐMany people have experienced that calcium is building up inside pipes, etc. จC this is also due to galvanic element effect.กฑ

Our main advice about material choice is to look carefully at what is supposed to be used in different conditions and listen to the experts.

กฐWe see many cases where customers specify bronze. And yes, we can use bronze, but we prefer to use nickel aluminum bronze, because it is more rigid. And itกฏs also better for avoiding galvanic element corrosion. So, this is the DESMI choice.กฑ

กฐOne last word in this materials section, and that is related to how to increase the pump efficiency. Most pumps have an efficiency of 75-80%. Some ship owners require 80-83%. And this demands more than just an update of the mechanics. While there are many ways to do this, coating a pump internally with a glass-like coating is the most common method. It is also possible to use an electrical control system to increase the efficiency. More and more shipowners are asking for the higher efficiency.กฑ

Electrical considerations

It is super important that traditional electrical installations follow the relevant classification society rules and standards from the International Electrotechnical Commission (IEC). This includes factors like correct installation, correct cable dimensions and correct cable temperature classes. กฐThis all has to be checkedกฑ, and you must have self-extinguishing cables in case of fire. Cables must also be halogen-free. Big cables or small wires จC they all have to comply with the same rules and regulations.กฑ

Ground connections must be done carefully, with the correct cable dimensions. กฐNo cheatingกฑ, we say. กฐThat means, bottom line, the size of the ground connection wire must almost be the same as the main supply wire. So, if youกฏre using a 3x50 mm2 power cable, then you must as a minimum use a 1x35mm2 cable for ground connection.กฑ

A rule of thumb is to use the same wire cross section in grounding wires as used in the power supply cable to the individual components.

We would also like to urge consideration of where the potential ground connection is made. กฐThere must be no potential electrical differences between the grounding point for the same equipment. That means that if you have a motor starter, then the ground connection for that motor starter driving that pump is the same spot as where you put the ground connection for this electrical motor. This is also known as equipotential grounding. Because if you put them 10 meters apart, you can be very sure that thereกฏs a difference in the electrical potential. กฑ

"Thereกฏs a common belief that just because you weld something to a steel plate, there are no differences in the electrical potential. But they are huge. Just the welding itself makes a difference.กฑ

For electrical protection of pump and motor, there are two settings that are critical:

The molded case circuit breakers (MCCBs) must be correctly adjusted and correctly installed. Settings on the MCCB is the maximum current stamped on the electrical motor.

Setting on the thermal relay is according to the pumpกฏs non overload power, which is given from the pumpกฏs test sheet.

So, the MCCB protects the installation and the thermal relay protects the pump.

 Frequency converter

The advice, and rules and regulations about using a frequency converter follows the above recommendations for traditional electrical installations. But you must take extra considerations, since the frequency creates electrical noise that must be managed. กฐMake sure you at least have a common mode filter on a frequency converter when you do an installation. Larger installations may require du/dt filter.กฑ

You must also make the correct adjustment of maximum current for a frequency converter จC the same as you would do for the thermal relay in a traditional starter.

And then, when you want to use a frequency converter to operate your electrical motors, then you should seriously consider to increase the temperature class of the electrical motors to be one temperature class higher. กฐNormally, the choice is Class F, which is 135กใC.

But when operating with frequency converters this will make your motors warmer due to the switching frequency on the motor supply line. So, we recommend: go up to Class H, which is 150กใC. That will give you a bit more room to maneuver. And pricewise, itกฏs small money.กฑ

The cooling fan and IE2

Furthermore, make it standard that you want to measure the winding temperature inside the motor. That means that your motors should come with PT100 sensors embedded. Then we can measure it directly. And also, as this motor is often running at a very different RPM, then make sure you have an electrically driven cooling fan on top, instead of a standard mechanical one. Because when you run the motor at a low RPM, you donกฏt have the same cooling capacity as you do when it goes at normal speed. But if you put in an electrical fan, you will have the same amount of cooling, no matter the speed of the load.

กฐWhen using a frequency converter, consider seriously using normal rated IE motors จC or standard efficiency motors. The reason for this is that you donกฏt gain anything by increasing the IE class on the electric motor, if itกฏs connected to the frequency converter. Because the summarized efficiency of the grid will stop at the frequency converter, meaning the gridกฏs efficiency on the supply line is determined by the frequency converter. And the price difference between IE2 and IE3 or IE4 is significant.กฑ