specialized hydraulics for water loss management: hydraulic transients … · 2017. 12. 19. ·...

Significant hydraulic transients occur when there are substantial changes in the momentum of the water travelling in a pipeline which can occur for a variety of reasons including:

sudden break of a pipeline or component thereof;

sudden pump stoppages as typically occur with a power failure;

sudden valve closures;

rapid withdrawals from the system;

any other occurrence that changes the velocity of water travelling in a pipeline; and

any combination of the above.

Hydraulic TransientsIn most water systems, transient flow is the rule, and steady state is the exception…

Pump starts & stops

Pump Start Pump Stop

Negative Pressures

Magnitude & Frequency

Making changes to one part of the system affects other parts…always.

Pressure Reducing Valve (PRV) Adjustment → Change in Pumping Station Behaviour

Hydrant Operations

30 psi

Transients and Leakage

Leaks are …. Good for transients

Bad for efficiency

Without good transient control and proactive maintenance programs, we are chasing our own tail

Transient Pressure Monitoring

A transient pressure monitor consists of a: high frequency pressure transducer, smart data logger, and a host of additional equipment depending on the nature and complexity

Consists of the installing one or more transientpressure monitors in the field

Controlling Transients

Hydropneumatic tanks

Air is used to absorb transient pressure surges

Variable FrequencyDrives (VFDs)

Examples from Mexico of pump operations with and without VFDs


Air Valves

Surge Relief Valves

Pressure Reducing Valves (PRVs)


Maintenance Important!

Sample monitoring data

PRVs in Practice

Upstream of PRV

Downstream of PRV

40 psi drop

<10 psi drop

TransientUnnoticed…

Pump TestingMeasuring Flows Without a Flow Meter…

Thermodynamic Pump Testing Method

Thermodynamic Method

Measure Power (P)

Measure TDH (H)

Estimate hD and hM

Measure Temperature Gain DIRECT MEASUREMENT OF

Pump Efficiency hP

Calculate Flow (Q)

PMD

HQP

hhh

Measured

Wasted Energy Converted Largely to Heat Energy(Temperature Probes Capable of Measuring Accurately to 10-3 K)

TemperatureProbe

PressureGauge

Flow Measurement& Meter Verification

Example 2:Station meter over-registering flow

Implications: • Calculated NRW higher than it

really is, so…• Utility looked for leaks that

didn’t really exist

Example 1:Good correlation between station meter and thermodynamic method

Major Billing Meter Error

!

CFD Analysis

8 Pumps Mixer

Butterfly Valve

Differential Pressure Flow Meter

Results

Hydrodynamics at meter important!

Influenced by:

Pumps in operation and their locations

Appurtenances

Replace differential pressure flow meter with magnetic flow meter

Add flow straightener

Construction planned

The FixMagmeter

Flow Straightener

Other advantages ofThermodynamic Pump Testing

Of particular importance to water loss professionals:

Individual pump flow metering

Accurate hydraulic modelling

Energy reduction & optimization

Etc.Overall

Efficiency Gap

Efficiency Loss

Manufacturer’s Best Efficiency Point

Tested Best Efficiency

Point

Typical Operating

Point

Excellent Agreement Problem…

You cannot manage what

you don’t measure.

specialized hydraulics for water loss management: hydraulic transients … · 2017. 12. 19. ·...

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