Your HVAC system’s suction conditions must be optimised for optimal performance, and air ingress is the enemy. Having properly aligned pipework is also essential in avoiding reliability issues and poor air quality. Using the the incorrect reducer at the suction and discharge line is a common reason for projects suffering from major suction and discharge issues.  

If you’re a project manager, make sure your plumbers are kept in check, and that your reducers are correctly specified and installed! 

The Role of Reducers 

Reducers are simple fittings that allow you to connect pipework of different sizes to one another. 

Eccentric and Concentric reducers have their unique roles and are categorised based on whether the midpoint of their opening and closing points are parallel. 

Concentric Reducers  

Concentric reducers are categorised by their central shape, with the midpoint of their small end being the same as the midpoint of their large end. 

Concentric reducers should be used on the discharge line of your pump. Their symmetrical design facilitates properly aligned connection of pipework to your pump system.

Do not use concentric reducers on the suction line of your pump, as this will cause air bubbles and cavitation. 

It is imperative that concentric reducers are never used on the suction line! The Hydraulic Institute of North America, Pump Industry Australia and Masterflow all see eye-to-eye on this matter… Please take our advice, and save yourself a tonne of headache!  

Eccentric Reducers 

Eccentric reducers are categorised by their asymmetrical shape, with the midpoint of their small end being different to the midpoint of their large end. 

Use eccentric reducers on the suction line of your pump. They are designed to protect your system against air bubbles, and they do their job very well! 

Avoid using eccentric reducers on the discharge line of your pump, as this will likely cause pipework misalignment. 

Make sure your plumber understands THIS! 

It is imperative that the far-too-common mistake of installing concentric reducers on the suction line of your pump is avoided at all costs!  

Concentric reducers being used on the suction line leads to air and gas bubbles forming in the pipes that connect to your pump, leading to cavitation. Cavitation puts your seals, bearings and O rings at risk of failure, creating leakages and losses in pressure. 

Furthermore, these air pockets limit the cross-sectional area of the pipe, increasing liquid velocity. Increasing liquid velocity in turn ramps up frictional losses on the suction line, which is a common catalyst of pump failure. 

Instead, using eccentric reducers on your suction line ensures that air pockets have nowhere to form on the suction line, protecting you from the enormous headache, downtime, and costs to your pocket and reputation that are suffered when air pockets plague your system. 

Keep this in mind both when drawing up a system, and when plumbers are conducting installation.   

To conclude, it’s as simple as remembering: 

Eccentric = Suction (think of the C’s in eCCentric and suCtion!), and Concentric = Discharge (Think ‘CD’; Concentric Discharge).