Z-type Overflow Pipe

From ReefPedia

Contents 1 DIY Z type overflow pipe 2 How it works: 3 Initial starting of the overflow piping 4 Flowrate of the Z type overflow pipe

DIY Z type overflow pipe

On the left is the diagram of the DIY Z-type overflow piping that can be used for aquarium that does not have holes drilled at the bottom of the tank. The design of this overflow piping once primed will still retain its siphon even when the return pump is stopped. As you can see from the design the water level in the tank partition will only drop, up to the level of the Tee joint.

How it works:

During normal operation the overflow pipe ( this design is commonly known as Z pipe) is filled with water and the siphon break pipe is empty.

When there is a power failure or the sump return pump is switched off the water level in the tank partition (baffle is black colour piece in my diagram). The water level will drop until it is the same level as the "tee" joint between the suction break pipe and the discharge pipe to the sump.

The water level in the tank partition is above the opening of the intake of the overflow pipe. Thus the water will be trapped in the overflow pipe shown as blue colour in the diagram.

When the power supply is back or the sump return pump is switched on the water level of the tank will increase, also in the tank partition area. The water level will raise above the "tee" joint, the siphon effect kicks in and the overflow pipe returns to normal operating condition.

Initial starting of the overflow piping

This is the method I used

• 1. temporarily close the opening of the siphon break pipe.
• 2. suck the air out using a siphon pump at the discharge end of the overflow pipe.
• 3. once the water is flowing out, remove the temporary seal of the siphon break pipe.

Another method of starting of the overflow piping

• 1. temporarily close the outlet of the overflow pipe
• 2. fill the overflow piping with water from the opening of the siphon break pipe.
• 3. temporarily seal the opening of the siphon break pipe.
• 4. open the outlet overflow pipe while the siphon break pipe still remains closed, the water will start to flow into the sump and start siphoning from the tank.
• 5. open the siphon break pipe

Flowrate of the Z type overflow pipe

The maximum flowrate of the Z type overflow piping depends on :

• 1. the height difference between the water level and the "tee" (bigger height difference higher flowrate)
• 2. the size of the pipe (bigger pipe more flow)
• 3. the friction loss from the piping and fitting.

However the actual flowrate for the system will depend on the flowrate of the return pump. If the return flowrate is too high for the Z type overflow pipe you can either increase the diameter of the pipe or use more than 1 overflow pipe.

Problem with reduced flowrate when the hole at the end cap is too big or the end cap is removed

One of the problems encounterd is when the hole in the end cap is too big or it is removed the flowrate is reduced greatly.

This is because the water level difference for the siphon is now only between the water level in the overflow compartment and the Tee joint. As the bigger height difference the higher will be the flowrate.

Sometimes this causes the maximum flowrate achievable by the overflow pipe to drop below the return pump flowrate. This is a major problem and if not resolved can cause flooding.

Solution

The solution I have is to connect an air tubing from the hole to about 1 to 2 cm below the water level of the overflow compartment. This maintains a negetative pressure in the piping and thus the water level height difference is now increased from the tank water level to the outlet of the overflow pipe. However if the return pump fails the water level in the overflow compartment will drop until it passes the air tubing opening. Siphon break will occur at this point to ensure sufficient water remains in the overflow pipe to kick start the siphon once the return pump cuts in.