Chris said:
....
Thank you for all the replies.
The system we have is this:
The RIGID pump is 1/3 HP, and is the main pump. There is also a backup
pump, a Basement Watchdog. These are plumbed inline. Here is a really
crappy picture of the setup.
http://farm4.static.flickr.com/3206/...9b75d367_b.jpg
In that picture, the discharge for the Rigid pump is on the right, the
basement watchdog on the left.
At this point I am not convinced all is hooked up correctly though.
When the pump stops, there is a clunk, which I can oly assume is the
water closing the sump pump.
Each of the 2 pumps has it's own check valve, and they are directly at
the pump discharge.
Thanks for all the replies. Maybe I should add some gravel or rocks to
the bottom of the pit and raise the pumps themselves. These were
installed by a contractor, and a competent one at that 
The basement watchdog pump worked very oddly when we got alot of
water, som I am not sure if that was a worthwhile investment. It is
currently unhooked because it alreasy needs a new battery (1 year
old).
Chris
Decent looking installation and a pic's worth a thousand words:
Unless it's a semantics issue, the pumps are installed in parallel, not
inline. One pump does not push anything through the other pump, which
would be the case were they "inline".
Can one safely assume that, were the cover removed, and the pump
outlsetS clearly visible, that the check valveS would BOTH be right
there and visible? From the pic, I can't see anything that looks like a
check valve.
If so, BOTH check valves need to be functional or either one would
allow water to run back into the pit. If either one leaked, the water
would just flow right back into the pit, maybe even siphoning extra
water from wherever they connect to outside.
In order to use only one check valve, it would have to be in the
horizontal pipe, to the left of the place where the two pumps connect
into the horizontal pipe. And I'm sure I don't see a check valve there.
If the check valve is farther away than the pieces shown in the picture,
then it's mislocated and simple air in the pipe/s/outlets could flip one
of the other open on you and you might get a slow return from a poor
closure.
IMO:
1. Either get two check valves in there, one at each pump, or, remove
one pump and plug its pipe so nothing can flow either way. The latter
makes it harder to put the emergency pump back into service though, so
makeing sure each one has a good check valve is better.
2. If the bottom of the sump isn't clean, has sand, floor grit, fur,
wet dust dust bunny fur, small pebbles that can get into the pumps, then
those can easily defeat the check valves by getting stuck and tangled up
in and around them. Sump pump regular debris screens are almost never
fine enough to keep out debris that would let a check valve be
compromised. And sand will wear it very quickly.
So perhaps a good cleaning of the pit is in order, and possibly the
addition of a galvanized screen around the two of them so there is
plenty of surface area on it, but a much smaller grid opening size, to
keep out normal flooring debris. But get the water-return problem fixed
before worrying about this one.
3. The dead battery: Died within a year? Was it kept properly
charged/topped off as per the installation instructions? It's hard to
see but I don't see any charger connections, IF it is supposed to need
one, which I suspect it is. If the charger is there & I just can't see
it, do you know it works?
4. Last and least likely, are you certain the water is coming back in
via the pipes to the pumps, or is it leeching in somewhere
in/under/along the floor/walls? I had a very similar problem once,
changed the check valve and no help: It turned out the water was
seeping back to the wall from outside and coming into the floor tunnels
and then running into the put. All the water routing is underneath the
cement, so you couldn't easily just look at the ditch and see the water
running; I had to remove inspection caps to look for it.
It's a fairly simple solution, whatever it turns out to be, and just as
simple to diagnose, once the right thngs are looked at. Try getting the
house quiet and just sit and watch it run thru a cycle or two while it's
doing that. Between your eyes, ears and mental visualization of what's
happening,, the problem and thus the solution may jump right out at you.
Question: Where does the water go outside? How far away, above or
below the grade of the exit thru the wall, etc.?
Are you certain the check valve/s are working? Yes, that clunk
usually indicates the valve closing; but are there two of them and is
the second one staying closed and correctly closed? Etc.
HTH
Twayne