Tools Talk: Working with CO2


05 July 2018
Dave Kingston, Aspen Pumps Group Training Officer, looks at the equipment needed to work with a refrigerant that is growing in popularity.

CO2 (R447) offers the lowest practical GWP (global warming potential) of all the common refrigerants and as such is rapidly growing in popularity, given the GWP quota reductions the industry is tasked with implementing. 

The tools required for installation and maintenance need to be heavy duty, due to the pressures associated with this refrigerant. JAVAC supplies a full range of manifolds, charging equipment and leak detection specifically designed for the application.
The R447 filling rig comes with two cylinder connections for both vapour and liquid filling and care should be taken to identify which piece is applicable to which cylinder. The vapour filling rig (subcritical) is a cylinder regulator which must not be used on a CO2 liquid fill cylinder, otherwise it will cause internal damage to the internals. This rig also has a separate valve after the regulator for fine flow adjustment and this will help slow the liquid flow and stop the pressure dropping too quickly and freezing the cylinder to the ground. 

The liquid filling rig (trans-critical) is less complex and is an adaptor with a relief valve that connects the HP anti-whip hose to the system. Of course it must be remembered that when charging trans-critical systems a vapour charge of around 7bar must be applied to the system first, in order to avoid dry ice forming inside the system as the pressure drops through the charge valve.

Manifold sets for both commissioning and servicing are higher spec than usual, given the higher pressures R447 operates at. For subcritical systems a two or four valve manifold is available, utilising class1. glycerine filled flutter-less gauges. The hoses are rated to a suitable working pressure and a higher bust pressure than normal. In order to achieve the optimum efficiencies in CO2 systems a higher accuracy is required and greater care needed when connecting tools and equipment.  

Digital manifolds such as the Refco DIGIMON and wireless TAP are pre-loaded with the R447 scale, which is easily selected from the 55 refrigerants scale menu. 

For trans-critical systems a two valve manifold is supplied, featuring heavy duty valves and hoses with a working pressure of 210 bar and a burst pressure of 840 bar. The class1. Gauge scales display LP 0-80bar and HP 0-160 bar, respectively.

Evacuation is standard and a suitable pump from the JAVAC CC range is fine. It’s critical that extensive evacuation is undertaken to ensure the system is as dry as possible and an OFN triple evacuation is mandatory and for this the OFN RS750 Rig is a great option.

Leak detection needs some care and the JAVAC D-TEK Select CO2 infra-red leak detector is the best option and operates between 3-6 gr/an; bubble spray is not suitable for R447 leak detection. As CO2 is a background gas it takes a little more time to allow the instrument to calibrate. In a plant room the leak detector should be turned on. It takes around 30 seconds to calibrate to the background gasses and establish an intermittent beep; this happens every 7-10 seconds. From here it can be slowly moved towards a suspected leak. When it alarms again, wait until it automatically re-calibrates and proceed further. If it’s too sensitive due to a large leak, the low sensitivity button will reduce this by 8 fold and make it easier to proceed towards the leak. Always re-select high sensitivity as soon as the leak is identified.
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