On Thu, 23 Nov 2006 00:35:05 -0500, mm
wrote:

I finally realize that I need a battery powered back up sump pump, and
finally have time to install it.

I want to use 2 check valves and then combine the output into the
existing output pipe.

1) I'm not sure I will be able to do all the piping within the sump:
The sump came with a perfect plastic plug that has room for the
pedestal pump, the float rod, and the output pipe, but no room for
anything more, no room for another pipe, and the plug is such that the
notch in it can't be enlarged or the plug will fail, collapse or
something. So I want to do the connections inside the sump. And
have only one output pipe like it is now.

The sump is 17 inches in diameter and there is room on the floor of
the sump for both the old pump and the new one.

The sump is 18 inches deep. Is that likely to be enough?

2) Is it a mistake to do it this way? Should I put a second output
pipe in parallel with the current one, at least until I get out of the
house? Once in 27 years there was so much water coming into the sump
that my 1/2? HP pedestal pump wasn't enough to expel it all, and the
sump overflowed.

The battery operated pump will run at the same time the AC pump runs,
but maybe the standard diameter output pipe will restrict the output
so that the total won't be much more than the one pump does now.
Should I put a second output pipe in parallel with the current one?

Thanks.

The standard method is to join both output pipes with a wye a couple
of feet above the pumps. You need a separate check valve for each
pump above the pump and below the wye. Remember to drill a small (1/8)
hole below each check valve to prevent air-lock.

You may be able to do this in 18" but it will be tight. Probably
easier to drill another hole in the sump cover for the extra pipe, and
then wye them together above the cover. (You will have to slit the
cover, or be willing to dissassemble the piping at the check valves to
get the cover off, though.)

You generally don't want both pumps to run together all the time. Set
the switch for the backup so it comes on a few inches above the on
point of he main pump. Then the backup will only run if the main
fails or can't keep up with the flow.

The water carrying capacity of the output line depends on many
factors, lift, pump pressure, how long the run is, etc. If it's cheap
and easy to run a second line it's cheap insurance, but it wouldn't
typically be necessary. But a single 1.5 inch line probably won't be
able to handle the full rated capacity of both pumps running at the
same time, so if you really think both pumps will run a lot of time,
then you use double lines. But that is a *lot* of water.

HTH,

Paul