Filter Physics

[pkppv]

Ok, so I'm in the process of designing a trickle filter, but there is just one problem. Many trickle filters use the siphon effect to get water from the tank to the filter and then a pump to get the water back to the tank. Say there is a power outage or the pump malfunctions. Would the siphon effect not empty the tank all the way down to the siphon tubes depth and thus flood my floor or perhaps even my whole room? I don't know much about these kinds of filters but these are my potential resolutions.

1) Use a very shallow intake depth. Therefore during an outage only a few gallons would overflow and if you had your trickle filter in a large bin this would not be a problem. This teqniques would present difficulties in keeping the flow equal, so one would have to put the pump that returned the water at a shallow depth in the reservoir and make sure it was faster than the siphon. I'm not sure if pumping air is bad for a pump, so perhaps this would in fact be a terrible idea...


2) Use two pumps, one to take the water out of the tank and one to return in. This would be useful as it would keep the intake and output speeds equal at all times if the pumps were the same. A shallow intake depth would work for this as well, but if a large bin for potential overflow is not available, then you could design a system that pumped the water up out of the tank then let it fall into tubing below. This would eliminate a potentially dangerous siphon effect as there would be no pressurized connection from the tank to the filter.

-I have heard of an overflow box, but Im not really sure how it works.

Have these methods been used? What works best for intake? How does an overflow box work? Thanks a lot!

 

[pkppv]

No one has any ideas?

 

[Tolak]

1) An overflow does not siphon, it removes the added water that goes above the level of the overflow. Some are set up similar to a self siphoning overflow, but once the tank water level reaches a predetermined level it stops overflowing. The flow rate is determined by the pump adding water, not the overflow removing it. In theory it's no different than the overflow in a bathtub or bathroom sink. As long as it is set up properly, and can handle a higher flow rate than the pump can produce the tank will not overfill.

2) You will never get two pumps totally balanced equally as far as flow rate is concerned. They can be identical pumps, eventually one will pump slower or faster. This means either the tank or the sump will overfill.

The best from a water/flood management standpoint is double drilling the side of the tank, installing bulkhead fittings, and piping these to the sump. Set up the sump in whatever way you think is best for filtration, add the pump, pipe that back to the tank. Fill the sump to a suitable level, plug in the pump, good to go. There are many methods used on the bulkhead fitting to reduce noise, skim the surface, and so on, but for reliability that is your best bet, less is more.