My apologies, I didn't see anywhere previous in the thread where you mentioned that it was not feasible to run without the check valve due to your current sump size.

No apologies necessary. My fault for lack of information.
You are totally right whatcaneyedo my mistakes in the start are a pain in the a$$ now and I will have to break it down and do it right, but it has to wait till after the holidays at least. For now...band aid.

OK you guys got me thinking, maybe I could go with no check valve if I can reduce the amount of water backflow into the sump by raising my return outlets...hmmm

Yes...that is what you need to be thinking about to eliminate the check valve.

Here is the type of Check Valve I use this
http://www.bulkreefsupply.com/store/...lve-tu-112.jpg

I have it mounted horizontally and it works perfect........I needed one cause Having anti syphon holes on a dart with a single outlet would spray water all over the place and when I placed them lower in the water then my sump would overflow so I had to go with a check valve.

Thanks for the info Kevin....as far as this problem goes it's on the back shelf now since I just cracked my sump!:mad:

As a quick fix.. you could change out the elbow above the checkvalve for a Tee, and put an arrestor above it. if you really want a quick fix you could even just drill and fill it in. Any building supply store generally has them, they're used for basement faucets, toilets, washing machines, stuff like that. They come brass or plastic, washing machine ones are generally plastic, and only run you about $20-$30 (yeah a lot for a chuck of plastic with an air cushion behind it). Also noticed the double elbows for what looks like power cord access, this could be the main problem of the water hammer, if you take that out while fixing your sump just throw a flexi pipe for the corner and you might dodge the problem completely. Anyways, good luck with the sump :D

I use this check valve as well and mine hammers right now. It did not on my other tank though. It must be a plumbing problem I made the return higher in the tank with a flex line so it only hammers for a bit now untill the water drops.

re
 

yeah, that sounds like it would work. if you drill a hole right below the waterline (the lowest point of water that can be drained without overflowing the sump) the hole will let in air cutting the siphon...

hey man you can always use a piece of foam to allow the air to get in and still have the water get defused alot.

exactly and try to dril a hole on a angle if you can. and drill it on the back of the pipe so if it does spray it will hit the tank and not go out front.......