SLD pump avoids oversizing

2 min read
The NAUTILUS 27 will supply flow for boilers up to 27 kW and being a positive pump it 
maintains flow over a range of heads.
The NAUTILUS 27 will supply flow for boilers up to 27 kW and being a positive pump it maintains flow over a range of heads.

It is common that circulating pumps are run near to closed valve to generate sufficient head, this moves the efficiency point from a best efficiency of  perhaps 70% to more frequently 25%. The aims of EuP 2015 and ErP are therefore somewhat diluted. With a positive pump the flow can be pre-selected to match the boiler and the pump will only take the power needed for that particular installation. This is an opportunity to move on from Edwardian plumbing connections and the need for cumbersome wrenches and on to press-in and compression couplings. It is also an opportunity to move on from Permanent Split Phase Capacitor motors to the more efficient BLDC motors, avoiding the capacitor and resulting in a more compact layout and a lower input voltage. The motor is programmable. There is a move towards 24V and 48 V in some industries.

Excellent NPSHR

The 27 Nautilus, at 150 mm x 80 mm x 50 mm fits in line, needing no mountings and in particular the direct end inlet to the impeller gives excellent NPSHR. Two discharge connections give flexibility to the layout, both can be used; pressure switches, expansion vessels and relief valves can use the pump as a manifold.  Flow 1.2 m3/h ( 20 l/m ), heads to 8 m (0.8 bar ). Industry standard service valves can be used, again saving space. 15 mm or 22 mm  standard copper is suitable. A helpful feature is the ability of the impeller to pass air without air-locking; the commissioning of a system and subsequent trouble shooting are eased. The open passageways,  which pass a 6mm diameter solid, reduce the risk of debris from the installation and commissioning problems and subsequent call-outs. Being entirely rotary, without reciprocating or eccentric parts, the axial flow Archimedean screw impeller has a smooth, steady way of delivering its performance.

Head loss calculation

Trevor Benjamin, former technical director of SLD Pumps, says: "I have come across the problem users have in calculating the head losses in a system and the natural reaction to 'Fit a big one'. This negates much of the effort of pump and motor designers to improve the efficiency and the EuP 2015  Directive." "The central heating trade is prone to this and one way of helping is to have a pump that provides a flow matched to the boiler, not to a guessed head from the installation. A positive pump does this and takes only the power needed for installation. Being positive the axial flow Archimedean screw impeller is an answer and modern CNC machining makes it a simple manufacturing process. I have prototyped the pump in 3D manufacturing and it performs well.  I would like to see such a better approach to efficiency considered," continued Trevor.