Machine Design

Software guides piping designs and pump selections

To maintain a competitive edge in today's engineering market, you have to take advantage of sophisticated computer technology. DesigNet software, for example, helps engineers more efficiently design water and wastewater systems.

A piping and pump model in DesigNet shows a general layout for a wastewater system. Picking any icon in the diagram brings up a detailed descriptions of pumps, valves, controls, and performance at that location.

Prior to its purchase, we performed hydraulic calculations by hand or using less-sophisticated software.

The hydraulic-modeling program performs macroscopic fluid-flow calculations in the design and analysis of complex piping networks that handle liquids or gases. It uses physical properties, theoretical fluid-flow equations, and widely accepted empirical formulas, such as the Darcy-Weisbach formula and Bernoulli's equation. The software contains data on pipes, fittings, common piping components, and valves, as well as data on over 50 commonly used gases and liquids.

The software can create, modify, and manage data files. It also lets users manipulate data for fluid properties, pipe and material specifications, component information, pumps, and unit conversions.

Despite the method or tool selected, the same preparations are necessary to evaluate a piping system. The first step is to gather information, such as piping layout plans, identifying fluid properties, site conditions, flow-rate ranges, and construction materials. Doing this by hand would mean gathering engineering tables and manufacturers' data sheets to determine individual losses through each piping component. The software, however, has a library of that. It contains fluid properties for over 50 common liquids and gases, and can simulate networks with up to 9,000 branches and 1,000 tees. User-specified fluid properties are easily added. The program lets users individualize it to a specific water or wastewater stream, right down to fluid properties, such as temperature, pressure, specific gravity, density, and viscosity.

As designs progress, inevitable changes affect entire calculations. When done by hand, these recalculations can be extremely time consuming. But changes to computer models are easily made and the software recalculates in a fraction of the time previously needed.

We recently designed and constructed a new industrial wastewater system with the software. Part of the job was to size pumps, piping, equipment, and instruments associated with the system, and estimate system-line losses. The computer model considered three new end-suction centrifugal pumps that drew wastewater from a 12,000-gallon storage tank and sent it to any of seven destinations.

The model estimates required horsepower for transfer-pump motors. The computer output is used to develop a system curve that helps select the right pump. The model was helpful in establishing pumping capacities for the maximum flow condition, and could easily be manipulated to determine performance for average and minimum-flow conditions as well.

This eliminated hand calculations for different flow rates and site conditions, such as pumping from an empty tank versus a full tank, or pumping to a combination of destinations. It also was helpful in estimating inlet pressures for properly sized flow-control valves.

The model was set up into suction and discharge sides of the pumps. This arrangement made it easy to determine pumping capacity required by simply subtracting the pressures across the networks where the pumps would be.

In addition, we sized pressure gages using the model to estimate the correct scales for the gages. Because the model provides velocity information, it's also a quick way to properly size pipe.

The software provides standard and customized reports, a definite advantage. These are excellent ways to document calculations and provide neat and concise updates to clients. Reports can include equations, summaries, and intricate tables detailing every system component. And graphics can illustrate information throughout each step of the network, such as friction losses, pressures, flow rates, velocities, and pipe diameters.

The user-friendly program has an extensive Help menu and technical support by phone. We have always found the support personnel to be responsive and technically proficient. When help is needed on tough problems, a command downloads the model file into a debug file, which can be emailed to the developer. Help files also contain example problems, which serve as tutorials.

-- Nancy Zacharek

Nancy Zacharek is a project engineer at O'Brien & Gere Engineers Inc., Syracuse, NY ( The company provides start-to-finish engineering, construction, analysis, specialty manufacturing, and operations and property-development services to industry, municipalities, and government agencies.

TAGS: Hydraulics
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