Pump Shutdown Frequency Ramping to Prevent Water Hammer
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Solution Overview
Problem
Existing methods for turning off pumps, especially those handling wastewater, result in water hammer effects and energy wastage due to the generation of vacuum bubbles and premature closure of non-return valves, which can damage the conduit and consume unnecessary energy during prolonged ramp-down processes.
Innovation Solution
A method where the control unit ramps down the pump frequency to operational frequency minus at least 10 Hz over a reflection time for the conduit, ensuring the terminal frequency is not less than 10 Hz, and then stops the pump to prevent further energy consumption and minimize water hammer effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the pump frequency is ramped down from operational frequency to zero to eliminate water hammer effects, then water hammer impacts are reduced, but energy consumption increases due to prolonged operation at low frequency
Solution Approach 1:
The patent applies partial action by ramping down the pump frequency only to a terminal frequency above zero (not completely to zero) and then stopping the pump. This partial ramp-down approach is sufficient to reduce water hammer effects while avoiding the energy waste of prolonged operation at very low frequencies, thus resolving the contradiction between reducing water hammer impacts and minimizing energy consumption
2Object-affected harmful factors
If the pump frequency is ramped down slowly to eliminate vacuum bubbles, then vacuum bubble generation is reduced, but the turning off time increases
Solution Approach 1:
The patent applies preliminary action by performing a controlled frequency ramp-down before stopping the pump. This preliminary frequency reduction prepares the system by minimizing vacuum bubble generation during the subsequent pump shutdown, allowing for a faster overall turning off process while still protecting against vacuum bubble formation
3Object-affected harmful factors
If the non-return valve is allowed to close during pump shutdown, then water hammer effects are reduced, but the valve may become damaged due to slamming
Solution Approach 1:
The patent applies beforehand cushioning by ramping down the pump frequency before the non-return valve closes. This gradual frequency reduction cushions the pressure changes in the system, preventing the non-return valve from slamming shut and becoming damaged, while still allowing the valve to close and reduce water hammer effects
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces water hammer impacts and energy usage by ensuring the pump stops without performing non-useful work, protecting the conduit and non-return valves while minimizing energy consumption during shutdown.
Implementation Method 1
If the supply of liquid from the pump to the conduit is abruptly stopped a pressure wave in the liquid will be generated that is transported through the pipe system
Implementation Method 2
when these implode, e.g. different parts of the liquid moving in different directions in the conduit, so-called water hammer will occur that risk damaging the conduit and its units
Implementation Method 3
the flow rate of the liquid is in general in the range of 0.7-1 meter per second, entailing the presence of a large liquid flow having a large momentum in the conduit
Data Source
AI summary
A pump station arrangement and a method for turning off a pump configured for pumping liquid via a conduit. The pump, before being turned off, being driven at an operational frequency (FN) by a control unit. The method is characterized by the steps of, ramping down the frequency of the pump due to a turn off instruction, the terminal frequency of the ramping down being equal to the operational frequency (FN) of the pump minus at least 10 Hz and the ramping down time being at least a reflection time (TR) for the conduit in question, and the terminal frequency of the ramping down not being less than 10 Hz, and stopping the pump after the ramping down.