Read QAoctober02 text version


As seen in PHPI

OCT 2002

Air Vents & Air Separators

Q. Why is air so detrimental to heating systems? A. Air in any system, whether it is open vented or sealed, will

have a bad effect on the system and its components. Air contains oxygen and when this mixes with water and comes into contact with radiators it can cause corrosion, which if left unchecked can cause the radiator to leak. Air in the system can also cause noises in boilers, particularly low water content boilers; such noises are often referred to as `kettling'. Air can also cause undue wear on pump bearings and on motorised valves.

Q. Surely if I put a corrosion inhibitor in the system

that will solve the air problem?

A. Corrosion inhibitors may prevent corrosion and the

formation of gases such as hydrogen, which are a product of corrosion, but they will not prevent entry of air into the system if there is a fault in the system design or installation.

Q. What is the most common cause of air entering a

heating system?

A. In an open vented system incorrect design and positioning

of the circulating pump is usually the cause. The open vent connection should be located between the cold feed connection (which is the neutral point on the system) and the circulating pump, i.e. on the suction side of the pump, so that `pumping over' does not occur. It is generally best to locate the circulating pump in the flow so that the system is generally under positive pressure and this prevents air being drawn in around gland seals on radiator valves. Another source of air ingress is on the pump inlet union; always make sure that this union has the correct packing gasket and is fully tight.

Air Separator from Reliance®.

Q. Would it not be better to use a sealed system instead of an open vented system? A. There is nothing wrong with open vented systems provided they are correctly designed and installed, although in mainland Europe they are almost unheard of and sealed systems are the norm. Sealed systems are better in the long term once the initial venting and commissioning of the system is completed, but it is important to size and position the expansion vessel correctly so that it can accommodate all the expansion volume of the system when it is heated. Q. I find that it seems to take ages to eliminate air from large heating systems. Can I do anything to speed up the venting process? A. Time is at a premium on every job and commissioning costs can be saved if an automatic air separator is fitted in line, ideally directly after the circulating pump to expel air and other gases.


Can aeration be caused if the feed and expansion cistern is too small?

A. Yes, if the cistern is too small to accept the expansion

volume of the system when it is heated, it will overflow and then when the system cools the volume will contract allowing the float operated valve to open and introduce fresh oxygenated water into the system.

RELIANCE WATER CONTROLS® The Safety Valve Specialists


Air Vents & Air Separators


I have a system, which has some pipes that form a high point on the system. Can you recommend a suitable automatic air vent for this situation?

A. The RWC AVEN 012 series of automatic air vents have 3/8" or 1/2" MBSP connections for fitting vertically in pipework, and consist of a polypropylene float connected to a simple valve. When the build up of gases within the float chamber exceeds a certain level the float drops, opening the valve and releasing the gas trapped within the chamber. As the gases are released water enters the chamber and raises the float, closing the valve. The vents can be supplied with or without automatic shut-off valves. Q.

Is there a vent that will vent quickly on initial system fill?

Construction diagram of the Reliance® Air Separator.

A. Yes, the RWC AVEN 013 series of fast bleed dual control automatic air vents are similar to those described above but incorporate a manual purging button, which when pressed allows a much higher volume of air to be discharged.

The air separator consists of a central wire mesh baffle, which intercepts and breaks up the flow of water, releasing the gases into the vertical section of the separator. When the quantity of gases accumulated exceeds the calibrated pressure, the float lowers and the gases exit automatically. The RWC ASEP series separator comes complete with a protection cap to prevent accidental venting, and is available in sizes up to 2" and is suitable for a maximum operating pressure of 6 bar. By removing the cap and internals you can use this device as an access point for dosing the system with cleansing and anti-corrosion chemicals.

Fast Bleed Dual Control Air Vent from Reliance®.

Q. A.

How does an air separator work?

Reliance Water Controls® Ltd

Worcester Road, Evesham, Worcs WR11 4RA, UK. TEL: +44 (0)1386 47148 FAX: +44 (0)1386 47028 SALES DIRECT LINE: +44 (0)1386 712400

This system diagram illustrates where you might typically fit an air separator and a fast bleed dual control automatic air vent.

All information is accurate at the date of publication (on the front page of the guide). Reliance ® reserves the right to make changes to the product which may affect the accuracy of the information contained within this leaflet. Reliance Water Controls® Limited are part of Reliance Worldwide®. ©Reliance Water Controls®, 2002.

RELIANCE WATER CONTROLS® The Safety Valve Specialists



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