Suction from closed loop

[Jessbo]

I installed a closed loop into my system to rid myself of powerheads. I am running an Ampmaster 3000 through six 3/4" bulkheads, two inlets, four outputs. All the plumbing is done in 1.5" PVC, just the bulkheads are 3/4". I have overflow strainers on each inlet, but the suction is pretty strong. My snails, and sometimes hermits get stuck, and turn into processed fish food. Just last night had a newly purchased perpermint shrimp turn into chum.

The strainers I have inside the tank now are about 2" long, so would increasing the length to 3.5" lessen the suction? Or do I somehow need to increase the size of the bulkheads? The tank is acrylic, but enlarging the holes in the tank would be no easy task!

 

[reedman]

You are starving the pump. 1.5" pipe is equivalent to 4 3/4" pipes. By using 2 3/4" pipes for your inlet you aren't even providing the equivalent of a straight inlet.

Solution:
1) Add at least 2 more 3/4" inlets (preferably 4 to lesson the suction).


2) Enlarge the size of the two 3/4 inlets to two 1.5" inlets. This is the best solution in my opinion.

If you don't do something you are going to burnout the pump or cause cavatation.

 

[Jessbo]

Hope I won't burn out the pump. Thought ampmaster was ok to throttle back. I would like to just enlarge the to holes I currently have. Much more of a pain the drill more holes, change plumbing, etc. Any ideas of how to enlarge the hole without ruining the tank surface? I have tried that on a piece of wood before with not so great results.

 

[reedman]

If you can drain down the water to the point of the bulkheads, you can clamp 2 pieces of wood (one inside and one out) together and use a hole saw to cut the new holes. This will ensure a good circle cut without skipping around. I haven't done this on a tank, but I have done it on wood and it works fine. Just take your time and be careful. Others should chime in too and you may want to see if someone else has done this.

 

[Jessbo]

I was thinking about the same process, but the bulkheads are about 10" below top of tank, so no real way to clamp wood together, of even a piece on the inside. I have a central overflow so maybe could put a piece of wood over hole, use pvc pipe to wedge against board and overflow to hold in place. Don't need to use much pressure to risk damaging overflow you think(using pilot bit on hole saw)?

Also, edge of 3/4" bulkheads are about 2" from joint. So new hole would be around 1" from joint. Would this jeopardize the seal at all?

 

[IAP Brian]

In theory, moving closer to the overflow edge shouldn't hurt, but if the tank is bowing, I would not recommend it. Have you considered moving away from the current suction inlets and drilling new holes? That would be the best solution if you have room. As far as the Dolphin pump goes, you can throttle it back as much as you would like.... on the pressure or outlet side, any restriction of the suction or inlet side is a very bad thing. I have gone round and round with Dolphin about their "prefilter" solution to the leaky seal issue. I don't like to put foam filters on pump inlets. If you have access to an inductive amp meter, you can have fun watching the pump work harder and harder with restriction on the suction side.
reedman is right on with his warning and his method for providing a new guide for the hole saw. I also have welded a piece of scrap acrylic around the hole and drilled through both for a new hole. Weld on 16 works great for this, but the down time for your tank would be too long for your livestock unless you moved them for 8 or so hours.

 

[Jessbo]

Would like to enlarge the current holes rather than drill more, and have two unused bulkheads looking, well, silly. The inlet holes are on the sides of my tank which is 48x24 so there is no bow. Will try a board pressed against the inside to guide my pilot bit, take it slow, and go from there. Least amount of down time with my tank.

Guess that would also explain why my tank temp is so high for me not having a heater. Would throttling back the output reduce the strain on the pump until I can solve this problem this weekend? Have I done any permanent damage to the pump as a result of its current operation?

 

[reedman]

I would recommend shutting the pump down and running some powerheads until you can remedy the intake issue. You run the risk of damaging the pump (or at best shortening its life) if you continue to run it with a restriction on the intake.

Glad Brian popped in. Good validation from someone who really knows acrylic.

 

[Jessbo]

So even dialing down the output won't help to reduce the strain at all? Will try and get things rolling tomorrow, since this issue is quite serious!

 

[jsmkmavity]

you dont need to clamp the wood or acryllic with the larger hole, you can just hold it by hand. two people would make the job easier. if this is not an option maybe you could run an extra return over the top temporarily and tie it into the return pipe.

 

[reedman]

So even dialing down the output won't help to reduce the strain at all? Will try and get things rolling tomorrow, since this issue is quite serious!

If this was any other pump but an ampmaster I wouldn't be so worried, but ampmasters (though good pumps) are meant to run wide open without any restriction on either side. They are especially sensitive to restriction on the suction side. You could do an over the top 1.5" intake like the other poster suggested. I run mine this way and it works great. Would be a good solution either short term or long.

 

[Jessbo]

Well I am taking the time today to re-drill the holes. Going to be a feat, will keep you all posted on the progress. I have the ampmaster shut down now, hoping to save any further damage.

 

[reedman]

Good idea. Good luck with the drilling. I'm sure it will go fine and you'll be very happy with the result (long life on the pump, cooler running temps, and increased flow)

 

[tomz]

If you want to make the original holes larger cut a 1.5" hole in a scrap piece of acrylic, take the inner circle that you're left with and superglue it (superimposed) over the 3/4" hole in the tank. It then works as a great guide for drilling out the new larger hole.


Tom

 

[Jessbo]

tomz what a great idea! But thought more about the flow in my tank and decided to just close of the original bulkheads and drill two new 1.5" inputs. Got these large diameter screen to cover the opening. So should have next to no suction to grab my little ones.

Used a 2.5" hole saw bit, and remember from long ago how bigger hole saws can bind up easily. Was a real pain in the butt, but they are both done, just waiting to refill tank and turn pump back on.

Thanks to all for your help!