00:18
An open water column of 10 metres means that the lower pressure gauge measures a positive pressure of 1 bar. This is the weight of the water column. The upper pressure gauge shows no pressure.

00:27
When warming up, the volume increases, but not the mass of the water. Thus the lower pressure gauge still displays 1 bar. The upper pressure gauge shows no pressure.

00:51
A mixture of water and glycol expands more than water alone. This is an important point to remember.

01:07
The open water column is closed; this is comparable to a sealed heating or cooling system.

01:10
The application of heat means that the water will expand. The water cannot escape, and the pressure displayed on both gauges now rises quickly. There is a difference of 1 bar between both pressure gauges.

01:27
An expansion vessel is connected to the water column. The gas charge is equivalent to the weight of the water column.

01:50
The expansion water is absorbed in the vessel; as the gas cushion compresses, the pressure rises, but stays within specific limits.

02:26
If a larger vessel (with a larger gas cushion) is selected, the pressure will rise slower.

The heating system can be imagined as a square structure that is

Filled to the top with water, without the weight of the water column increasing - static height.
show in green 00:09

When the system is brought up to pressure (initial filling) the pressure remains the same throughout and counts towards the static height.
show in blue 00:15

A circulation pump is needed to move the water (for hot/cold transfer) through the system.
show in black 00:19

To counter the pipe resistance, the pump delivers positive pressure.
show in red 00:25

The pump's function will create a slight underpressure on the suction side of the pump.
show in yellow 00:25

The neutral point is where positive pressure (red) changes to negative pressure (yellow). The pressure remains the same whether the pump is inactive or not. The expansion tank can be fitted here.
show "N" 00:32

If the vessel is fitted any further from the pump, the positive pressure will be absorbed by the gas cushion in the vessel. The benchmark point moves. Less positive pressure on the delivery side, less suction pressure at the pump.
show from 00:37

If there is insufficient pressure on the suction side of the pump, cavitation may result. Various system problems may occur.
show from 00:47