Negative Head Systems
A negative head system exists when there is insufficent pressure or head of water under gravity to provide a flow / pressure at the outlet. Typically a negative head condition exists where the flow from the outlet is less then 1 litre/min.
Positive Head System
A positive head systems exists when sufficent pressure is available under gravity to provide a flow at the outlet. Typically a positive head condition exists where the flow from the outlet is more then 1 litre/min.
Pumps are rated in 'bar' which is the meausre of presure, 1 bar pressure being equal to 10 metres static head of water. Generally the higher the bar rating the higher the performance. However it is important to match the correct size of pump with the application to ensure optimum performance.
The following can be used as a general guide for applications:
- 1.0 bar pressure = Low boost
- 1.5 - 3.0 bar pressure = Medium boost
- 3.0 bar pressure = High boost
Twin pumps are designed to boost both hot and cold water supplies equally
Single pumps are designed to boost single water supplies;
hot , cold or pre-mixed
Standard pumps operate under positive head conditions only. A standard pump is operated by a flow switch,automatically starting when a gravity flow of water greater then 0.6-0.8 ltrs/min throught the outlet is detected. The pump will automatically stop when the outlet is closed and the flow ceases.
Universal pumps operate in positive or negative head conditions and do not require a gravity flow to start, incorporating both a pressure and flow switch. The pump automatically starts when the pressure switch detects a drop in pressure when an outlet is opened. The flow switch keeps the pump running as long as there is a sufficent flow of water. When the flow stops, the pump continues to run for 3 seconds allowing the system to re-pressurise.