ARCADIS Mechanical Engineer Interview Questions, Process, and Tips for Experienced

Affinity laws describe the relationship between pump performance and speed, flow rate, and head.

• Affinity laws state that if the speed of a pump is changed, the flow rate and head will also change proportionally.

• The laws can be used to predict the performance of a pump at different speeds without having to conduct actual tests.

• The three affinity laws are: 1) Flow rate is proportional to speed, 2) Head is proportional to...read more

NPSH is calculated by subtracting the vapor pressure of the fluid from the absolute pressure at the pump suction.

• NPSH stands for Net Positive Suction Head.

• It is a measure of the pressure required at the suction of a pump to avoid cavitation.

• NPSH is calculated by subtracting the vapor pressure of the fluid from the absolute pressure at the pump suction.

• NPSH is important to ensure the pump operates efficiently and does n...read more

Total head required for a pump can be calculated using Bernoulli's equation

• Determine the flow rate required

• Calculate the friction loss in the piping system

• Determine the elevation difference between the pump and the discharge point

• Add the three values to get the total head required

• Consider any additional losses due to fittings or valves

Standard oxygen transfer efficiency for fine bubble diffusers is typically around 30-40%.

• Fine bubble diffusers are commonly used in wastewater treatment plants to transfer oxygen to the water.

• Factors that can affect oxygen transfer efficiency include bubble size, diffuser design, and water temperature.

• Efficiency can be improved by optimizing these factors and ensuring proper maintenance of the diffusers.

• Typical oxygen ...read more

The recommended pipe material for 48% NaOH is high-density polyethylene (HDPE) or polyvinyl chloride (PVC).

• 48% NaOH is a highly corrosive substance that can cause damage to certain pipe materials.

• HDPE and PVC are resistant to the corrosive effects of NaOH and are commonly used for transporting this chemical.

• Other materials such as steel or copper should be avoided due to their susceptibility to corrosion.

• The temperatur...read more

Designing a wet well pumping station involves several steps and considerations.

• Determine the flow rate and head requirements

• Select appropriate pumps and piping

• Design the wet well and sump

• Include safety features such as alarms and backup power

• Consider maintenance and accessibility

• Ensure compliance with regulations and standards

Accessories used in a pump suction and discharge line

• Strainers or filters to prevent debris from entering the pump

• Valves to control the flow of fluid

• Pressure gauges to monitor the pressure

• Flanges to connect the pump to the piping system

• Flexible connectors to absorb vibrations

• Check valves to prevent backflow

• Expansion joints to compensate for thermal expansion

• Flow meters to measure the flow rate

Duplex stainless steel is good for NaCl 2500 ppm fluid due to its high corrosion resistance and strength.

• Duplex stainless steel has a high resistance to corrosion and pitting

• It has a high strength and toughness

• Other materials like carbon steel and copper alloys may corrode in NaCl solutions

The gradient required for free flow in a sewage pipe depends on the pipe diameter, flow rate, and type of material used.

• The gradient should be steep enough to ensure that the sewage flows freely without any blockages or backups.

• The gradient is typically expressed as a percentage or ratio of the vertical drop to the horizontal distance.

• For example, a gradient of 1:100 means that for every 100 meters of horizontal distan...read more