Water Cooling Equip. and Performance Guide – Pumps

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Welcome back to the second article in our series about water cooling. In this article we will examine pumps. We’re going to learn about pump ratings, pressure, efficiency, and true flow among other things.

As with much of life, the options involved in choosing a pump are myriad. You can find pumps that run off either AC or DC. You can find pumps that run submerged or in open air. You can find pumps rated for flow ranging from one gallon per hour (gph) to over 100,000 gallons per minute (gpm). OK, so realistically you can find pumps rated over 500 gph. In my line of work, I actually use pumps rated in the 5000 gpm range, but that’s another story. If you look hard enough, you can find fixed displacement and variable displacement pumps. I’ll only discuss centrifugal (variable displacement) pumps.

If you’re going to make an intelligent decision about which pump is right for you, then you need to understand what all the options mean.

AC vs. DC

Let’s start at the top of the list and talk about AC and DC pumps. This is really the easiest of the topics to understand and evaluate. AC pumps “plug into the wall” and draw power from a standard wall socket. Depending on where you live, this may be 50 or 60Hz and 110 or 220 VAC. From the pure power standpoint, you only need to verify that the pump power requirements match those supplied where you live.

DC pumps are also available, but typically must be custom wired to run off of a DC power supply. Provided the required voltage is 12 VDC, you may be able to run the pump off your existing computer’s power supply. Before doing so, you must check the power drain of the 12 VDC line. Anything in your computer that spins will draw some power from the 12 VDC line. Add up the total for your drives and fans and the pump making certain that your PSU can handle the load. It’s advisable to leave at least a 30% cushion to allow for efficient operation of the power supply and surges in demand as devices first begin spinning.

You should also know that the majority of 12 volt DC pumps are really bilge pumps. Most of these pumps are not intended for continuous duty and may fail prematurely in a 24/7 computer application. If you intend to use a DC pump, verify that it has a duty rating of 100%.

The vast majority of pumps you will find run off AC power. This is convenient because there is no concern of straining your power supply or having to buy an additional power supply just for the pump. This loses some of its convenience when you realize that there is no communication between the computer and the pump. The pump will run when it’s plugged into the wall. If you forget to start the pump, you (actually your CPU) could be toast. If you forget to unplug the pump, it will run needlessly after shutting down your computer. There are solutions to automatically start the pump when the computer starts and we’ll talk about them later in our article dealing with miscellaneous items.

Submerged vs. Open-Air

The next item in our list was submerged versus open-air pumps. As with the power source, each type has its own advantages and disadvantages. Let’s begin with submerged pumps. As you can guess, a submerged pump should run while sitting in a reservoir of water. Water from the reservoir gets drawn into the pump suction and discharged through tubing connected to its discharge port. Water returning from the computer dumps into the reservoir.

Among the advantages of the submerged pump are a bit of noise damping due to the surrounding water, generally cool operation of the pump as the water in the reservoir cools it, and relative ease in purging air from the circulation system.

The primary disadvantage of the submerged pump coincides with one of its advantages. As the water in the reservoir cools the pump, the water gets warmer. This has a direct impact on the temperature of the water circulated to the computer. As we’ll soon see, this is not as bad as it sounds. Other disadvantages include increased risk of contamination, air entrainment at the pump suction, and the space requirements of a reservoir.

An open-air pump has tubing connections for both the pump suction and pump discharge. It can sit just about anywhere that is convenient to route tubing. Water circulated in the system typically goes from the discharge, through the computer, and back to the suction side without a reservoir.

Among the advantages of the open air pump are accessibility, less energy input to the water, and convenient installation into a completely closed-loop circulation system. Additionally, open-air pumps require no reservoir and have a greatly reduced risk of air entering the pump suction.

Among the disadvantages are a loss of the sound damping that a water reservoir provides, greater difficulty bleeding air from the system, and a higher operating temperature of the pump. The higher operating temperature should not normally be of concern, but could be problematic if air circulation around the pump is extremely limited. This may happen if the pump sits in a desk enclosure, for example.

Note that all pumps that have a screen over the suction are intended to run submerged. The corollary that all pumps having a fitting on the suction inlet should run in open air is not always true. Some pumps meant to run submerged have a fitting rather than a screen over the pump inlet. These fittings allow the installation of filters as often used in garden ponds. Always verify that your pump is meant to run in open air prior to running it non-submerged.

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