More Than One Electric Water Pump - Series and Parallel - Everything you need to know

04/07/2019 12:00AM

There are times when running one Davies Craig Electric Water Pump just doesn’t quite cut it. These rare instances could be in really high stress situations, like a turbo four cylinder running some big rev numbers during a drift battle, where one EWP’s maximum flow needs to be higher. This could make for extra stress so perhaps a pair of EWPs that can flow at a greater rate than one single may be the answer? The competitive advantage of installing remote-mounted Davies Craig’s Electric Water Pumps is the EWP® is mounted in the bottom radiator hose propelling coolant through the engine’s cooling system totally independent of engine revs!


Is it worth mounting EWP®s? In order to make sense of this, what is the difference between ‘series’ and ‘parallel’ when it comes to installing a pair of EWP®. A simple way of looking at this is Davies Craig Electric Water Pumps can be installed in either in ‘series’ or in ‘parallel’. Using the car battery as an example, as illustrated below…

Batteries can be connected in either series or parallel like EWP’s. So, to acquire 12 volts, two x 6-volt batteries must be connected in ‘series’.  The same two x 6-volt batteries connected in ‘parallel’ produce 6 volts, but the current doubles. Relating these scenarios to EWP installations/connections to an engine – if we resemble head capacity to voltage, and flow rate to current, both types of connections have certain advantages;

Two EWP®s connected in ‘series’ (in line) doubles the head capacity of a single EWP®, while the flow rate remains the same as with a single EWP®.  Two EWP®s connected in ‘parallel’ (side-by-side) doubles the flow rate capability when compared to a single EWP® while the head capacity remains the same as a single EWP®

For example, Davies Craig customers with high cubic capacity, high horsepower engines are having marked success with two x EWP®s mounted in line. One is controlled by a Davies, Craig Digital Controller (Part no 8001) set to the engine’s targeted/set temperature and wired to the ignition. The other EWP® is operated by one of the Davies Craig Thermatic Switches, Part #0401, #0444 or #0500, wired directly to the battery and set to switch on at a few degrees above the Digital Controller set/targeted temperature, which should be set at a similar temperature as the manufacturer’s thermostat temperature, which can be removed or 2 x 5mm holes drilled in the plate.

Bill and his Infamous 240rsMaxi race car utilizes 2 Davies Craig EWPs

Let’s say that our totally nuts hi-po engine really pumps some serious horsepower. It probably means that cooling is good but could be better. Investigation shows that our current water pump is struggling and could do with a boost.

To be on the safe side, some high flowing units are investigated and let’s say the Davies Craig EWP150 looks like it might do the job. But we can fit two EWP115s instead to achieve around 230 litres of total flow and a pump that kicks in at a pre-set level to back up the first one.

This is where operating two EWP®s becomes like our battery analogy. One pump will flow 115 l/min, but you want two to flow approx 230 l/min, which way do you go?

In series two EWP115s will look like they’re flowing approx. 230 l/min, but it’s actually only the capacity that doubles, not the physical flow rate. In ‘parallel’ these two EWP® combine to flow the full 230 l/min yet appear to be, effectively, one EWP®.

Here we have a pair of EWP® that on their own will do a great job but only with engines producing less power than a performance engine. Two smaller EWP®s though can add that extra flow rate needed and can be set for one pump to continue flowing fluid to assist in the cool-down process after engine shut-down.

Are you running more than one Davies Craig EWP®? Show us yours and provide some background on our social media outlets.