Bidirectional tidal flow

[sphelps]

I should also point out that even with a cheap DIY mod the cost of adding the OM isn't much different than adding an additional pump. In order to accomplish this specific flow pattern I fail to see the advantage of adding something that requires more maintenance, adds more flow restriction and has less reliability. The OMs work great to simply alternate flow between a few outputs but in this specific case it's far from ideal.

[StirCrazy]

Originally Posted by MitchM

Steve,

How are you going to deal with stuff getting drawn into the suction bulkheads if you're using the same ones for discharge?


Mitch

thee will be strainer guards on them all. and I will not be running sand in the tank so I don't have to worry about that. I am also thinking of making some DIY live rock pannels for the back and sides. the side ones will hide the intake/discharges

Steve

[golf nut]

Originally Posted by sphelps

Yeah I'm not sure this will make a reliable system. If the drum always moves 100% freely then it'll be fine but unfortunately my experience with OMs is they can get a little sticky under pressure and with a small amount of debris. As far as I can tell this timer works by simply energizing the motor briefly to reset the switch, the idea is this brief pulse of power will move the switch and close the circuit thus resetting it, this is an open loop control system or one without feedback. If this is the case it will work fine in ideal conditions but put it in use and you'll have nothing but problems. When the drum stops it might not start moving immediately with a big pump downstream and a few grains of sand or whatever in the drum area. The drum rotates on magnetism so it's not a direct drive so sometimes it can slip a little before being able to over power the static friction. If the drum doesn't move immediately after being energized the circuit will remain open and the counter will start again even though the drum hasn't moved to the next location. This would be the case if the switch was measuring the actual drum location. If the switch is measuring the motor shaft location then the drum could slip throwing the whole thing out of whack, ie the drum will stop at a different position.

For the system to be reliable and work in real conditions you need a closed loop control system or one with feedback. A smart relay can accomplish this and they run for around $150. You should also use two separate switches that measure the actual drum locations so the relay can distinguish between the two positions which will further enhance the reliability.

If you have a jammed drum, then the smart motor or extra sensors will do nothing, unless they are smart enough to phone you and or take the unit apart.

When using a 2 way version the orientation of the magnet is changed deliberately so that it isn't possible to get out of whack.

[sphelps]

Originally Posted by golf nut

If you have a jammed drum, then the smart motor or extra sensors will do nothing, unless they are smart enough to phone you and or take the unit apart.

When using a 2 way version the orientation of the magnet is changed deliberately so that it isn't possible to get out of whack.

Correct if the drum is completely jammed but typically the drum will just need more than an quick pulse to overcome the static friction. The closed loop control has feedback and therefore will activate the motor until it actually moves and hits the next switch. Unlike the open loop which won't know the difference and could end up in an infinite loop. You could also program an error code with a closed loop control system so a lite or alarm is triggered if the drum doesn't move within a set time limit. All this is called error proofing which is an important part of designing a control system.

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[golf nut]

Originally Posted by sphelps

Correct if the drum is completely jammed but typically the drum will just need more than an quick pulse to overcome the static friction. The closed loop control has feedback and therefore will activate the motor until it actually moves and hits the next switch. Unlike the open loop which won't know the difference and could end up in an infinite loop. You could also program an error code with a closed loop control system so a lite or alarm is triggered if the drum doesn't move within a set time limit. All this is called error proofing which is an important part of designing a control system.

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In my lifetime I have built thousands of machines, I am well aware of dummy proofing.

I just did a simple test for you. the result is that if the drum stalls the sensor keeps the motor running, it isn't a quick surge, it remains running till the sensor sees the decay and the the timer starts once it sees the next magnet, if the magnet doesn't move the motor stays on.

[golf nut]

Originally Posted by sphelps

If you had a common suction 2 valves would work. I think ideally to create the cross flow you need a suction on one side and the output on the other so in this case you would need 4, which is what I was talking about.

Here is a quick bad video, there are 8 holes drilled , 4 at either end of the tank for coverage, the lower holes are C/L feeds, the uppers are C/L returns, they are being switched by a common drum, when water enters top right it is being removed bottom left and vise verse, if you watch carefully you can see the pellets being drawn in from the bottom. the pellets are an injection molding pellet about the same specific gravity as water.

just one pump.


http://www.youtube.com/watch?v=XxlOvNN-OPE

[StirCrazy]

Originally Posted by golf nut

Here is a quick bad video, there are 8 holes drilled , 4 at either end of the tank for coverage, the lower holes are C/L feeds, the uppers are C/L returns, they are being switched by a common drum, when water enters top right it is being removed bottom left and vise verse, if you watch carefully you can see the pellets being drawn in from the bottom. the pellets are an injection molding pellet about the same specific gravity as water.

just one pump.


http://www.youtube.com/watch?v=XxlOvNN-OPE

all that looked like was a ocean motion device with a common inlett and two outlets.

Steve

[golf nut]

Originally Posted by StirCrazy

all that looked like was a ocean motion device with a common inlett and two outlets.

Steve

Except is isn't, both the inlets and the outlets reverse to direct flow through the tank and also to be pulled out on the opposite end, each is aiding the other.

[golf nut]

This is one of a pair that were installed an a good sized tank in a public aquarium, these were equipped with proximity switches and then driven by a PLC, this would alternate flow as in the video but enable to turn the tank clockwise or anticlockwise when viewed from above, ideal in a through wall viewed tank.

[schroeder]

I have not checked into this but maybe there is another valve type that you could use.

I do service work on commercial dishwashing equipment. These machines sometimes use a valve that has a servo actuated diaphram to close 1 outlet (say the outlet to the wash arms) while opening the other (the drain).

They typically have cast ABS or PVC bodies but I cannot attest to the materials used inside the valve. I can however guarantee that they are under $250 and usually operate on 120V.

I'll try to get some contact info at work tomorrow and post if I find anything out.