Reservoir and Installation

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Why use a reservoir?

The use of a reservoir in a PC water-cooling system is optional. For many the advantages of using a reservoir outweigh the disadvantages. Reservoirs come in many different shapes, sizes and styles. Some contain a submerged pump while others do not and are connected inline. The Angel Eye Bay-Res is an inline reservoir. This means you can pretty much plumb it wherever you want in the water-cooling system. My personal preference is to have the reservoir connected directly ahead of the pump.

Advantages of using a reservoir:

  • Provides an easily accessible fill point
  • Serves as an air trap to help remove air bubbles
  • Provides a reserve volume of water to make up for losses that occur over time
  • Can help reduce NPSH (Net Positive Suction Head) of the pump
  • Allows for expansion and contraction of the systems water volume
Disadvantages of using a reservoir:
  • Can be bulky – may be hard to locate in small systems
  • Potential source of flow restriction and leaks
The two most obvious advantages of using a reservoir are providing an easy access point to fill or add water to the system and helping get rid of trapped air bubbles, especially during startup. When you first setup a system, there will always be some air bubbles circulating around in the water. These air bubbles must be removed for optimum performance (water transports heat a lot more efficiently than air).

As the water enters the relatively large volume of the reservoir, the water velocity will decrease (don’t confuse velocity with flow – the overall flow rate will remain constant in a closed system). Air bubbles can become trapped in a high velocity fluid stream and may only rise to the surface when the water velocity slows down enough to release them.

In general the higher the overall system flow rate, the larger the reservoir volume will need to be to effectively remove air from the system. Remember though, just because you may have a pump that is rated at 300 GPH free flow, doesn’t mean you will have anywhere near that amount in a real system. In addition to the total volume, the shape of the reservoir and use of baffles and/or screens can have a large affect on a reservoir’s ability to remove trapped air bubbles. The Bay-Res Rev. 2 incorporates a center baffle, which forces the water to flow down one side and back the other. This helps minimize turbulence and gives the air bubbles a greater chance to reach the surface.

One of the nice features of an inline reservoir is that you can place it most anywhere you want in your system. This means the Bay-Res can go in the top, middle or bottom drive bay. Now some people think that having the reservoir at the highest point in the case is best since air bubbles rise to the highest point, right? Well actually, no. Air bubbles will only freely rise to the highest point when there is no flow. The normal flow in an operating system is usually enough to keep air bubbles trapped and circulating in the coolant stream. Only when the water velocity decreases in the reservoir do the air bubbles have a chance to slow down and rise to the surface.


Installing the Bay-Res in an open 5.25” drive bay was much like installing a typical optical drive. The reservoir is held in place with the four supplied screws. Having a case that uses sliding drive bay rails is a big advantage – it allows quickly and easily sliding the reservoir out for filling or topping off the system.

Angel Eye Bay-Res Water-Cooling Reservoir - Cases and Cooling 10

If your case does not have sliding bay rails then you will have to remove the reservoir mounting screws before you can slide the reservoir forward for filling or topping off the system. Alternately, if the bay(s) above the reservoir are empty, that can also provide access to the fill port.

I generally find that mounting the Bay-Res in the lower 5.25” drive bay works the best for me as it keeps the reservoir below the optical drives (just in case we experience a leak) and the tubing more closely lines up with other components (like the waterblock). In reality, with the option of using either straight or 90º fittings, you can place it in any drive bay you choose.

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