Final Comments

As stated previously, hydraulic surges could have the potential to create a catastrophic failure at the pump station or within the pipeline. This aspect of surge analysis represents a substantial risk to not only the operators and client, but MWH Global. Under no

circumstances is the design engineer to design a surge mitigating method without the involvement of the Senior Hydraulic Specialist. No one solution applies to all pump stations.

Just because a similar size station has a pump with a flywheel, it does not mean another pump station requires a flywheel.

2.11. Deliverables

Once the design criteria are identified, the design engineer shall summarize and document the criteria in the form of drawings and calculations. Summarizing and documenting the design criteria serves two purposes. First it provides a benchmark to track future design changes either initiated internally or by the Client. Any future changes to the design criteria must be well documented in the design Change Log. Failure to capture changes prevents MWH from recuperating additional costs required for the rework. The second purpose is to provide a starting point for other disciplines to progress their individual designs. In order to avoid rework, the design engineer shall verify calculations have been peer reviewed prior to submitting calculations to other disciplines.

The following is a summary of the minimum design criteria required for internal use (examples of the deliverables are included in Appendix B):

 System flow and head information

 Fluid type, characteristics and material constituents

 Pipe Schedule

 Pipe sizing and velocity calculations

 Pumping Station System Schematic Diagram

 Hydraulic Profile

 Piping Preliminary Layout

 System-head curve with pump performance curves superimposed (PSET)

 System NPSHAVAILABLE calculation and NPSHREQUIRED (supplied by the pump manufacturer.)

 Pump selection and data sheet

 Wet well sizing calculations

 Valve and equipment schedule (including power requirements)

 Control Strategy Summary

System flow and head information

Define minimum, average and maximum system design flows. Determine static heads and friction losses.

Fluid type, characteristics and material constituents

Determine type of fluid, temperature, specific gravity and percent solution. Determine material constituents of fluid based from laboratory test results. Use material constituents as basis for material selection of pump component

Pipe Schedule

The pipe schedule is an MWH standard drawing indicating the piping materials used for each process fluid in the water and waste water industry. The pipe schedule is typically modified on a job by job basis. The design engineer shall identify and select the process fluid designations needed, identify the fluid abbreviation used, determine the acceptable materials for the piping and determine the appropriate pipe testing procedures. This information should be made available, by the design engineer, to other disciplines for consistency when identifying process piping on the mechanical, civil and instrumentation and controls drawings.

Pipe Sizing and Velocity Calculations

The design engineer shall provide calculations detailing the requirements of the piping upstream and downstream of the pumps. The requirements shall include the pipe size, wall thickness and flow velocity. The pipe sizes and velocities shall comply with MWH guidelines pertaining to minimum and maximum flow velocity.

Prepare Schematic Diagram of the Pumping System:

The Design engineer shall develop a schematic diagram for each pump train and the entire pump station. This diagram, similar to a flow process diagram, shows the quantity, location and sizes of equipment, fittings and valves, flow meters, back pressure valves and any other inline pressure loss devices. Included on this schematic diagram should be unique numbers corresponding to each valve, fitting, pipe section and miscellaneous pipeline items (i.e. flow meter) to aid the input of these items into the Pumping System Evaluation Tool (PSET) a hydraulic calculation program. Design engineer to refer to the appendix for an example schematic diagram.

Hydraulic Profile

The design engineer shall prepare a hydraulic profile and establish an approximate Hydraulic Grade Line (HGL) for the system. The hydraulic profile shall include the static elevations of the free water surfaces at the upstream and downstream boundaries of the system. The hydraulic profile shall also show the HGL at pump centerline at suction condition, and the HGL equivalent to the TDH of the pump plus the friction losses at the pump discharge. Refer to a sample HGL drawing located in Appendix B.

Preliminary Piping Layout

The design engineer shall develop a preliminary piping layout. The piping layout shall be a plan and section drawing of the pump station, indicating the equipment, valves and piping arrangement, pressure rating and wall thickness of piping. The layout shall take into consideration the required equipment and piping sizes, adequate clearance surrounding the equipment for maintenance and space requirements for ancillary systems. This piping layout shall utilize available information as it will be used by other disciplines to size the overall structure.

System-Head Curve with Pump Performance Curves Superimposed

As part of the design criteria documentation, the design engineer shall create a system-head and pump performance curve to evaluate the hydraulic fit of the pump to the system curve. The design engineer shall utilize the Pumping System Evaluation Tool to develop a system-head curve for the project with all known bends, elevations and fitting k factors. The design engineer may also want to consider including the pump performance curves from multiple manufacturers. The curve is to visually verify that the specified operating range, efficiencies and pressures can be met by the selected pumps.

NPSH Calculations

As mentioned previously, the NPSH margin is critical to maintain stable pump station operation. The design engineer shall formalize the NPSH calculations, and include a copy in the design criteria documentation. The calculations would be referred to if the operating levels for the pump station are ever modified. Furthermore, occasionally the submitted or test NPSH curves do not match the pump manufacturer’s catalogue information. The design engineer should have the NPSH calculations finalized and readily for comparison to the submitted pump manufacturer’s NPSHREQUIRED curve.

Pump Selection Data Sheet

Summary of equipment information shall be listed in a data sheet. The data sheet shall be distributed to all design discipline. Use the MWH Standard data sheet form.

Wet Well Sizing Calculations

To finalize the wet well hydraulics, the design engineer shall identify the type of wet well

configuration utilized in the design. Based on the design selected, the design engineer shall provide sizing calculations per the Hydraulic Institute Standards or the Flygt design recommendations.

Calculations should include spacing between the pumps, baffle walls and straight approach distance.

The calculations shall also include retention time at minimum flows, and storage capability during a power outage.

Valve and Equipment Schedule

The design engineer shall develop an equipment list. This is required as early as the Design Development Phase. The equipment list shall include the tag numbers, location, and type of

equipment, design capacity and head, motor horsepower, size of valves, pressure, actuator type and horsepower. Use the MWH Standard Equipment Schedule Form.

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