Hello all,

My name is Wills and I own a fig (the fruiting plant) nursery in Florida as well as an online fig discussion forum, not sure if mentioning the sites is allowed? so wont.

In one of my greenhouses have about 10,000 gallons of water for passive heat retention and I also grow tilapia in the tanks. I have two RDF filters which are 55 gallon barrels where the sides are mostly removed and that are covered in very fine stainless steel mesh, it feels like cloth. Each barrel sitting horizontally inside a 300 gallon tank. The water flows into one end of the barrels where it falls out of holes inside the barrel and only way out of that barrel is through the SS fabric hence the filtration. As the SS screen plugs up with debris the water level in the 300 gallon tank falls and there is a 4" PVC pipe outside the tank with a float in it and a threaded rod out the top and through a mechanical well pump switch that has an added longer arm. When the float falls far enough it triggers the switch which turns on a 12V motor (12v marine battery powered) and the belt around the drum turns it about 1/8 revolution, takes about 2 seconds then shuts off. There is also a spray bar above the barrel which then cleans the screen of the debris which falls into a gutter inside the barrel and the waste leaves the system. The spray bar solenoid is powered normally and controlled through a solid state relay triggered by the mechanical well pump switch. That all works great. The problem is....there is really no reason for the spray bar to come on each time as it is just a waste of water. Now if the spray bar did not come on the barrel would still do its thing and eventually the screen will plug all the way around to the point where the barrel turning does not make the water rise so the barrel will keep turning. It is at that point I would want the spary bar to be triggered to come on which would be a much more efficient use of water. I just don't know how to do that I had thought of adding a second switch either a micro switch or well mechanical pump switch to each tank that triggers at a lower water point but that seems clunky and there has to be a way to do it that the spray bar solenoid (24V) does not activate unless the barrel turns for XX seconds?

The electronics are not in the greenhouse but in my attached shop so would be a dry location. Any guidance or ideas would sure be appreciated. I can build most anything but electronics of this sort I am not so comfortable with.

 

Well you could build a divider circuit so the spray only activates every 2nd 3rd etc time the barrel rotates.

 

I'm thinking a delay timer using a 555 timer chip as in the attached schematic. You will need to figure out where to use the relay contacts in controlling the spray bar solenoid.
Steve G

 

I appreciate the help but sadly that is way outside my comfort zone, I would not have the first clue how to build what is depicted in that schematic. I may be reaching too far and may have to do it with a more mechanical solution sadly.

 

I appreciate the help but sadly that is way outside my comfort zone, I would not have the first clue how to build what is depicted in that schematic. I may be reaching too far and may have to do it with a more mechanical solution sadly.

I could build it and send it to you if you want. Use "start a conversation" when you click on my avatar.
Steve G

 

You can purchase time delay relays that will do what sghioto suggests above. Cost in the neighborhood of $10 from surplus/salvage houses to $100 +/- new. What you want is an ON-Delay relay with 12 volt power, sufficient contact rating for your spray solenoid valve and adjustable time delay covering any possible delay you may end up selecting.

Consider the Grainger stock # 33VC05, 12V coil, 10 amp DPDT (Double Pole, Double Throw) contacts, 3 seconds to 5 minutes adjustable ON-Delay, $54.75. <https://www.grainger.com/product/MACROMATIC-Time-Delay-Relay-33VC05?breadcrumbCatId=> There are many other similar units out there but this one seems to fill your needs inexpensively. If it does not come with an "octal" socket you will have to buy one. Many models come with solder terminals. You will want to check current draw on your spray bar solenoid valve but I can't imagine it is over one amp.

Just to be safe, consider putting a reverse diode across the relay contacts to absorb any voltage kickback from the solenoid valve coil at turnoff, assuming the 24 volt supply is DC. If it is AC you can't use a diode and have to put a low voltage (say, 33 volt) MOV surge suppressor or a 0.1 microfarad 50 volt ceramic capacitor across the relay contacts. (This cap value is a guess. Anybody with more knowledge should correct me.)

 

Well just for fun and giggles here's a second version of a delay timer about as simple as it gets.


Steve G

 

If I understand what you are saying, the drum doesn't turn 1/8 turn because the system is designed to turn it 1/8 of a turn, but rather it turns until the water level rises back up to the desired level and, if the screen is clean on the part entering the water, this results in the drum having turned about 1/8 of a turn.

If that's the case, then it would seem like adding a delay to the water sprayer will do what you want. You can purchase relays that have build in delays. It sounds like it takes roughly 16 seconds for the drum to make a full rotation, so setting the delay to something like 20 seconds will let the drum screen become dirty all the way around. Once the spray bar turns on, then it will continue to be on until the drum has turned something like one and an eighth turns more and the entire screen will have been cleaned.

A couple things I would be concerned about is whether or not the parts of the screen that have been out of the water and didn't get cleaned will dry out making it so that the spray bar can't clean them. They will get submersed in the water for just a couple seconds as the move around to the spray bar, but is that enough?

The other thing is what is happening to all of the water that is entering the barrel while all of this is happening?

 

there has to be a way to do it that the spray bar solenoid (24V) does not activate unless the barrel turns for XX seconds?

xx seconds all at once, or xx seconds accumulated over a longer period of time?

This might have gone by already - what about a small limit switch that is pushed once per revolution by a bump on the drum?

ak

 

This sounds like a job for a small PLC (programmable logic controller). You can certainly cobble together a system that would do what you want but a PLC is designed for industrial applications with good reliability. I'm not sure a home-built solution would have the reliability you need.

Here's a link that describes it a bit more.

 

WBahn makes a good point. With the system as is ("all that works great ",from Willsc description) maybe it's not a waste of water after all.

 

WBahn makes a good point. With the system as is ("all that works great ",from Willsc description) maybe it's not a waste of water after all.

Also, it is really wasting that much water. Right now the spray bar comes on for about two seconds to clear an eighth of the drum. After the modification, it sounds like it will come on for about 16 seconds to clean the entire drum. To first order, isn't it six-for-one and half-a-dozen for the other? Wouldn't the optimal solution be more closely approach by adjusting the spray bar's water usage and/or the drums rotational speed so that it cleans the screen adequately but not excessively as it passes?