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Sump pump backflow preventer needed?

johnjingles's picture

I have a basement sump pump. PVC pipe comes up from the pump 4 feet then 90 degree turn thru wall to outside (4 feet). Then 90 degree turn down 2 feet into 4" pvc that runs the length of the back of the house - above grade and simply empties out on the side of the house - 15 feet from the house. Do I need a backflow preventer on this and why?

(post #87674, reply #1 of 10)

What backflow would there be to prevent?

Is there any source upstream of that point of connection between the sump drain to the 4" line which could continue to flow and thereby find its way back into your sump in case the 4" line were plugged downstream of the connection?

In that case, it would be prudent to install a check valve in the sump drain line. The only exception would be if the branch drain from the sump doesn't make a solid connection to the 4" line, which is not likely.

If the 4" line serves only as a drain for the sump, there is no reason for a check valve or backflow preventer.

Edited 9/3/2009 9:42 am ET by rdesigns

(post #87674, reply #2 of 10)

I had a sump pump that I HAD to put in a check valve.  I placed it just above the pump itself.   This way I'm not pumping that 4' of water every time.   Without the check valve, that 4' tall column of water will just go right back into the sump pit and might start the pump again. 

" Although I have the right to remain stupid, I try not to abuse that right"

" Although I have the right to remain stupid, I try not to abuse that right"

(post #87674, reply #3 of 10)

In one sense, you will always "pump" the 4 feet of water--either at the beginning of the pump cycle or at the end. By having the check valve down close to the pump, the pump starts its cycle against a 4-foot head of water, which is no big deal because a 4-foot head amounts to less than 2 lbs/ against the pump.

Unless the vertical pipe is larger than about 2" diameter, the water that drains back into the sump would not usually be enough to activate the float switch.

(post #87674, reply #4 of 10)

 A little more info on that old pump of mine.. When I moved in, the floor drain to the outside had been blocked by the town when they installed new sewer lines.   The sump pump was always "burning up" and the previous owner had a few "spares" sitting around to drop in place.   Turns out that the "pipe from the pump to the outside was made from 3/4 ID plastic pipe!   He had "necked" it into the pump's 1-1/2 outlet.   Said pipe was then routed up 8' to a 90, and then out a basement window.  No check valve to be seen, anywhere.   I re-plumbed with 1-1/2" pvc, added a check valve at floor level.   That one pump then lasted for several years until I moved.   House, with basement, was built right in a swale.   It was like being in the middle of a creek. 

" Although I have the right to remain stupid, I try not to abuse that right"

" Although I have the right to remain stupid, I try not to abuse that right"

(post #87674, reply #5 of 10)

I bet you're glad to be out of there!

BTW, do you have any experience with those sump pumps that electronically detect water in the sump when it rises to a certain level--like 3/4"-- and then pump it down to another pre-determined level--like 1/4" according to label on the box on the one I looked at in Lowe's?

I'm asking because they're small, and I'd like to use one in my sump, which is, unfortunately, just a plastic 5-gallon bucket sunk into the concrete floor of my cellar. It's small, and easy for a float to get hung up.

I intend for it to be used only as an emergency floor drain.


(post #87674, reply #6 of 10)

 Actually , no, I haven't seen those kind of pumps.   A side note on that "house":  the next owner thought the drain I had sealed up should have been un-sealed so it could work.  Yeah, right.   The drain tile to the outside had been cut and sealed when the town install the new sewer line in the back yard.   When the new owner un-sealed the floor drain, surprise, the basement flooded.  When I had the drain sealed, the basement was dry enough to have a woodshop down there.   The "pit" the sump was in was just a hole in the floor, and had a block to keep the sump pump out of the mud.   You could sit there and watch water running in under the 3" thick concrete floor like a waterfall.   I did "dowse" the yard, and found a large "pool' in front of the house, the house was acting like a "dam" in the swale, with the basement acting as a sluice gate.  Got out of there as fast as I could. 

" Although I have the right to remain stupid, I try not to abuse that right"

" Although I have the right to remain stupid, I try not to abuse that right"

(post #87674, reply #7 of 10)

I always figured that without the check valve you won't get the full volume of the sump to work with. The pump will short cycle because at the end of each cycle the water will run back down partially refilling the sump you just pumped out. Psychologically at least it just seems less satisfying.

(post #87674, reply #8 of 10)

The pump would not short-cycle in the sense of not pumping the full volume of water that the setting of the float switch allows it to pump, but, of course, you're right about the fact that quantity of water that's in the vertical pipe would drain back into the sump. That amount is usually small since the vertical discharge pipe is usually 2" or less. So, we're talking about 1 or 2 quarts in most cases.

However, I am well-acquainted with the "psychological" aspect of it that you mentioned--I used to have a commercial kitchen style SS sink in my cellar, and I thought that would be a great place to kill, dress and butcher some rabbits that a friend of mine raised. He didn't have the heart to kill them on his own, but he knows I'm heartless when it comes to killing for food.

Anyway, the stuff that went down into the sump I could never get completely out by running more water, and the drainage from the riser pipe made it worse. I would end up opening the sump and scraping and scrubbing to get it clean.

I've since moved the sink up into the garage, and the cellar sump is just for emergency drainage.


(post #87674, reply #9 of 10)

No. Not enough head above the pump that the backflow would refill the pit to any degree, and no danger of water being forced back into the basement from other sources.

Of course, local code may require one, in which case it's a lot simpler to just install it than argue.

As I stood before the gates I realized that I never want to be as certain about anything as were the people who built this place. --Rabbi Sheila Peltz, on her visit to Auschwitz

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #87674, reply #10 of 10)

Thanks DanH

I did not think I needed one for my situation. The previous owner had the set up I inherited. I was working in the cellar a month ago and all of a sudden the pump comes on. Yes it was raining crazy for some time. The backflow preventer is installed with compression connectors and the whole thing blew apart - split right in two. Thank godness I was down there when this happened. I quickly unplugged the pump, tightened the compression connectors again and ran the pump.

I am going to redo the pvc and remove the backflow preventer - and I am going to install one of those Basement Watchdog systems.

Thanks for the reply.