Andrew Burgess wrote:

"Marty Bach" writes:

I installed a 20 gallon circular pond container. In the container, I
have a couple of cement blocks that support a ceramic garden planter
just above the surface of the water. A 1/2 tube from the pump (lying
at the bottom of the pond container) runs through the bottom of the
ceramic planter. The intended effect is for the planter to fill with
water and spill over the sides into the pond container below. The
distance from the pump to the discharge is about 3 feet in height. The
pump is 310 gph.

My issue is that the pump runs and fills the planter until it spills
over the side (as intended). It does this for about 25 seconds. Then
the pump reverses and sucks water back down through the 1/2 inch tubing
(slowly for about 90 seconds). Then the process starts over again:
filling the planter and spilling over the sides for 25 seconds followed
by 90 seconds of reversal.

One possibility is that the pump thermal cutoff trips, shuts the pump off
and the water just flows back through the pump. When the cutoff cools, the
pump starts again. The cutoff could trip if the pump is defective,
overloaded or overheating for some other reason like restricted intake.

Sounds right. Three feet is a _long_ height for a tiny 310gph pump to reach
(that size is usually designed for aquariums with no lift capacity) but you
can't measure to the _discharge_ from the pump. Pumping water from one
level to another takes only two variables into account: the height
difference between the _surface_ of the water from where your pumping and
the _surface_ of the water you're pumpping to ("static head"); and the drag
created in the pipe ("dynamic head"). Bending over the pipe makes _zero_
difference to the water pressure the pump operates against, but does
_increase_ the dynamic head. Dynamic head can be decreased by making the
hose as wide and as short as possible with as few turns as possible (and
_no_ right angle or tighter turns). Putting the pipe in the bottom of the
container, or over the side makes no difference - _but_ it makes it easy to
see what's happening. Take the hose out of the planter. Hold it level
with the top of the planter. Turn on the pump. If it keeps working, then
your pump can at least reach this level. More likely, it will run for 30
seconds or so, then stop.

The fact that you say it drains _slowly_ suggests to me that you're using a
much too small hose but it might just be clogging at the top.
--
derek