There is quite a number of pump types on the market, but the majority of users are choosing between the two most popular pumps: the D5 and the DDC. In 2016 we have also introduced the SPC pump, but we’ll do a more in-depth comparison in one of the future articles. Our support is usually bombarded with questions about the differences between D5 and DDC. Both the D5 and DDC pumps have quite an old base design and none of the two has gone through some major changes. It’s like “you cannot reinvent the wheel”. The only big change that we could see over the years is that both the D5 and DDC pumps got PWM support. It means they are now featured with a sophisticated way of controlling their speed. If you are fresh to the subject and want to know more about PWM, just take a peek at our “What is PWM and how does it work?” blog material.

Although the D5 and DDC labels define the base design of the pump, there are a lot of versions available. There are some fakes on the market, some companies make slight changes to the pump design, while others just slam their own brand label on it. EK Water Blocks is at the time offering world renown Xylem® water pumps to its customers, so you don’t have to worry about quality or authenticity of our D5 or DDC pumps. Now, let’s start with the basics and the key differences between these two pump types.

On the left-hand side is the EK-XTOP DDC 3.2 PWM Elite pump with a Plexi top included,

on the right-hand side is an EK-D5 PWM G2 Motor alone.

The D5 is more massive, it takes up twice as more space than the DDC. D5 pump offers a maximum theoretical flow rate of 1500 liters per hour with a maximum head pressure of 3.9m. EK-D5 PWM G2 Motor can be controlled by PWM. Head pressure in pumps is determined with a simple test – hanging a hose vertically and measuring to what height the liquid can be pumped.

The D5 spherical motor pump.

The key design of the D5 spherical motor pump is its simplicity. The only moving part in a spherical motor is a hemispherical impeller unit (rotor), which sits on an ultra-hard and wear-resistant ceramic bearing ball. The rotor itself contains a permanent magnet which is driven by the electromagnet coils placed under the metal shell. It’s a simple force interaction between the permanent magnet (rotor) and the electromagnet (stator).

The D5 spherical motor pump with its hemispherical impeller removed.

The magnetic rotor always balances itself ideally on the ceramic bearing. The pump is very robust and the parts exposed to the fluid are corrosion resistant, which provides an exceptionally long service time.

The DDC pump is probably the world’s first pump to be used in mass-produced liquid cooled workstations. Due to its small size and great output, the DDC pump easily found its way to the hands of liquid cooling enthusiasts. The DDC pumps that EK offers have a maximum flow rate of 1000 liters per hour with a maximum head pressure of 5.2m for the EK-DDC 3.2 PWM model, and 7m for the EK-DDC 3.25.

The DDC spherical motor pump.

DDC pump works on the same simple spherical motor principle as D5 unit. The only moving part is a spherical shaped permanent magnet impeller rotor, which is seated on a wear-resistant ceramic ball. The spherical ceramic bearing ball and the overall design removes the occurrence of bearing play (also applies to the D5 design). Since the rotor of a DDC pump is also magnetically held in the designated position, small particles of dirt and maintenance do not present a problem.

The DDC spherical motor pump with its impeller removed.

Both pumps, the D5 and the DDC are water lubricated. In other words, they use wet rotor design. Therefore, it is strongly recommended not to run any of these pumps dry. Also, both types of pumps should have liquid circulating through them with a temperature lower than 60°C.

The D5 and DDC pumps with their corresponding pump top parts.

Both pumps are compatible with a wide range of accessories, the so-called “pump top”. Custom D5 pump tops and DDC pump tops are usually made of acetal or plexiglass (acrylic). These parts bring additional flexibility and aesthetics to the pump itself, but can also positively impact performance.

The D5 and DDC pumps mounted with EKWB pump tops.

These pump add-ons have female G1/4” threads, which means you can choose any fitting you like. If you want to get more information on fittings, we suggest you check out our “Fittings and Tubing Guide” blog post. It is crucial to point out that both D5 and DDC pump and pump tops have predefined inlet and outlet ports which have to be respected in order for your liquid cooling loop to work properly.

Examples of pump and reservoir combo units, and dual pump mounts.

The list of combinations and additional parts is quite a subject on its own. There are various reservoir combo options for these pumps and we are not going to talk too much about them at this moment. If you are interested in that subject, we suggest that you visit the blog post „Should I get pump reservoir combo or should I buy them separately?“. The only two things we should mention are the dual pump top and dual bay reservoir. Having two pumps in one cooling loop can boost flow rates and performance, and lower operating noise. The other reason why some refer to using dual pumps is safety because a backup pump is always welcome. Pumps rarely malfunction, especially the D5 model, but not everyone is using liquid cooling for a part time gaming rig. When it comes to serious workstations or servers, having an extra pump is never a bad idea.

A 120mm Vardar fan along the D5 and DDC pump for size comparison.

As always, we are saving the most important for last, just to keep you reading. Aren’t we naughty? We have laid out the basics of the D5 and DDC pumps. The D5 can offer bigger flow rates at a lower pressure, while the DDC has higher pressure but lower flow rates. Also, it’s important to know that small DDC pumps can be a bit noisier than the D5 models. The DDC, being more compact, can also run a bit hot, and that’s why additional pump heatsinks are available on the market. These heatsinks are not necessary, but it is something that could reduce wear and prolong the life of the pump.

If you are building a complicated loop with many angled adapters and several water blocks, a pump with high pressure will have the advantage. If you are building a small form factor PC with limited space, again, the DDC would be the smarter choice. The absolute all-rounder might be the PWM versioned D5. It has high flow rates and it runs cool and silent. In most cases, one D5 can run for several years without breaking a sweat.