Tackling system failure at source

Published:  02 September, 2010

Maintaining efficient systems — Jamie Bomber

Oxygen and nitrogen in waterborne systems can be bad news and can ultimately lead to system failure. Jamie Bomber has the solution

Gases and debris contained in water continually passing through pipes can, over time, cause excessive corrosion to occur resulting in black sludge, erosion, balancing problems, noisy pumps, boiler failure, cold radiators and leaking pump seals— all of which can have a negative impact on the effectiveness of a system. Just a millimetre of scale in a system can reduce energy output by up to 18%. As a result more energy is used to counteract the problem, so the system becomes increasingly less energy efficient as the problem worsens.

Owing to its natural composition, water contains gases like oxygen and nitrogen. The combination of water, oxygen and iron can prove to be especially problematic by creating system corrosion or rust. In hard-water areas, especially, this problem can be far worse due to natural limescale build up.

When a system is first filled, the water can absorb nitrogen and oxygen from the air in the pipework. After the initial system fill, nitrogen can build up as an inert gas, which is caused by trapped quantities of residual air that dissolve as the system pressure increases — leading to the level of nitrogen in the water being up to three times the natural concentration. When the system experiences temperature rise, a reduction in pressure, or frictional loss due to circulation, the excess nitrogen can no longer be retained within solution (as per Henry’s Law), so classic problems with air will be experienced.

To avoid such issues, which can eventually lead to corrosion, it is worth considering installing a

specialist pressurisation system combined with an air and dirt separator to deliver a total solution to system problems by removing air from the water.

A pressurisation or expansion vessel consists of two key components — the welded steel vessel itself and a butyl-rubber bag that separates the system water from the gas cushion used to control the pressure. When water is heated it expands. Pressure in the system rises and the extra volume is pushed into the vessel where it is stored until the water cools down again and contracts. Then the air cushion under pressure pushes the expansion water out of the vessel back into the system.

One of the undesirable consequences of oxygen in piped systems is the formation of sludge.

To ensure gas does not enter the water, a butyl-rubber bag should be used to contain it due to its impermeable nature. Such a system prevents atmospheric gases from absorbed whilst ensuring there is no loss of pressure gas from the expansion vessel itself.

An automatic air vent, such as the Zeparo Top from Pneumatex is used during the initial filling stage to vent all air from the system, also reducing the possibility of radiator ‘gurgling’ from free gases that may become trapped in the system.

By adding air and dirt separators to a waterborne system it is possible to deliver a total solution that will ensure that the accumulation of air in stagnant water, gas bubbles and micro bubbles are removed. A combined air and dirt separation module can be fitted to the system to remove the smallest of micro bubbles, whilst also removing debris loose in the system, which may be as a result of rust or sludge build up in a system not previously monitored in this way.

Considering the negative effect such issues can place on a system, compromising the efficiency with which a waterborne system may work and subsequently also increasing operating costs, it is wise to think about how a pressurisation syst­em, especially one with combined modules, can be of benefit within a heating and cooling system, helping to avoid unhealthy operating procedures to ensure corrosion and boiler failure are a thing of the past.

Jamie Bomber is sales director of Pneumatex.

Deposits in pipework and system corrosion caused by oxygen reduce system efficiency and can eventually cause failure.

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