Vertical back flow preventer

I purchased a 3" horizontal back flow preventer to connect to the drain going to my grey water tank. Once the 90 degree 3" PVC elbows are installed, the setup is too big for the limited room under my sink.
 
I want to switch to a 2" vertical back flow preventer I found at home depot, which is the same style as this http://www.completeplumbi...sion-swing-check-valve .
 
My issue is that inside the unit there is a swinging door that I expect to be open (downward) so that the door will close (upward) is water fills the grey water tank. However when I inspected the unit up close in Home Depot, there is an arrow that points the direction of the water flow and text printed on the unit that says for vertical use "this way up". However, in the recommended position the door is closed (downward) and if water was to be flushed down the drain the back flow preventer would keep it from filling the grey water tank.
 
It just seems that the instructions on the unit are backwards. Has anyone installed a vertical back flow preventer?

test run the valve with a 3 feet piece of pvc pipe on the end with the end of the pipe pluged and fill with water and see what the valve does in both directions. Mike

Why are you using 3" pipe to drain to your waste tank?
When the waste tank is full, the sink will not drain, there is no pressure on the waste side, why the bfp?

chefbuba
When the waste tank is full, the sink will not drain, there is no pressure on the waste side, why the bfp?

 
it keeps waste water from contaminating the wash/rinse/sanitize water in the sinks

sorry I don't get it........if the waste tank is not full it wont contaminate the sink............grey water supposed to be bigger than fresh water so this should never happen any way... If grey water is plumbed correctly should have no issues??? Am I not seeing something?? it's early but..................

oohh no, i agree, thats just the only reason i could think of they would want it...
maybe sloshing around during travel ?

Buck & Vi's


sorry I don't get it........if the waste tank is not full it wont contaminate the sink............grey water supposed to be bigger than fresh water so this should never happen any way... If grey water is plumbed correctly should have no issues??? Am I not seeing something?? it's early but..................

It is required by GA health department. Here is a video on the BFP in a concession trailer in CA.
 
http://www.youtube.com/wa...u_in_order&list=UL

I found out that the vertical back flow preventers are meant to be used in a sump pump configuration where the water is meant to be pumped up and not flow back down into the well.
 
I decided to keep my 3" BFP but use reducing connectors to get the pipe down to 2".

Every place is different. First time I have heard of one. I would rather have that set up in place of the air gap I am required to have. It leads to spills on the floor under the sink. Worst thing that they could come up with..... an open septic system.

chefbuba


Every place is different. First time I have heard of one. I would rather have that set up in place of the air gap I am required to have. It leads to spills on the floor under the sink. Worst thing that they could come up with..... an open septic system.

 
I saw one of the open air gap setups, that looks like a mess. In the GA health interpretation manual, it mentions an air gap or back flow preventer. I am glad I have the option.