Sump Design

Intro sump design
The basic idea of having the pumps placed in a sump is handling the inflow variations. By not having a pump sump it is necessary to have pumps that can adjust automatically to the inflow. This requires an expensive control system and pumps have to be equipped with VFD or other system to regulate the pumped flow.

A proper design of a pump sump for submerged and submersible dry installed pumps is crucial for pumps life length. An incorrectly designed sump could potentially result in poor performance and/or mechanical strain due to vibrations and cavitation at the inlet to the pump(s). The main design requirement for a sump design is to provide optimal inlet conditions for the pumps, which means that the flow being delivered to the pump units is uniform, steady, and without swirl or entrained air.

Adverse phenomena  
Phenomena Effect on the pump performance
Non-uniform flow
Efficiency
Pulsating head
Noise and vibration
Unsteady flow Fluctuating load
Noise and vibration
Swirl Change in head, flow efficiency, power
Vortices Noise and vibration, Local cavitation
Entrained air Flow, efficiency,
Noise, vibration
Fluctuation in load
Physical damage
   
Designing criteria:
A sump should be

 
Reliable to handle inflow variations. The design depends on the magnitude of the incoming flow, levels of the incoming pipe and cycle time for the pumps. How the levels are finally set depends of the design of the sump.
 
Economical. The sump should be as small as possible in order to minimise the investment cost for constructing the station.
 
Designed to facilitate installation, maintenance and service work.
 
Adapted to the pumping media. The sump should have a design that prevents sedimentation building up. Having a clean sump implies less maintenance problems and costs.
 
Designed to provide necessary hydraulic conditions for proper work of the pumps.
Flygt recommendations
The most reliable way to achieve hydraulic requirements is to follow basic recommendations as:

 
Directed flow towards to the inlet of the pump
 
To avoid stagnant or low velocity regions
 
To provide adequate clearance from walls and between pumps
 
To provide adequate submergence
 
Protect air entrainment
 
Protect pre-swirl in the sump
 
Additional considerations for waste water pumping stations
 
Sloped floor
 
Including cleaning cycles
In order to handle these requirements during the design process of a sump, Flygt has developed a number of design recommendations as well as software that can support designers, planners' etc with the design of sumps. These brochures and software are detailed in the following sections.

Model Tests

Modeling Tools

Sump Volume Calculation

The TOP Station

When Are Models Necessary?