I would say that drop is not normal. It implies that it is sucking
air as soon as the pump is turned on.

In addition to the other suggestions, possible air leaks can occur in
the seal on the shaft, the gaskets in the pump housing, and the cover
gasket for the prime pot.

My experience with problems like this is the amount of air in the
prime pot DECREASES as the pump runs and the flow of water into the
pot captures the air and it is drawn into the impeller and discharged.
The fact that it takes the pump some time to lose it's prime implies
the flow is restricted, either on the input or the output.

One approach is to slowly pour water over all possible leak points and
observe if it appears to be sucked in. Another would be to cap the
ends of the system and pressurize. A third would be to rig a
temporary run of pipe from the suction side of the pump to the pond
and see if the problem goes away. Yes, all of these are messy.

PlainBill

On 6 Sep 2006 08:00:35 -0700, "Bob" wrote:

I am not able to watch the level of water get lower in the prime pot,
so it must be a very slow process. I'm still trying to determine how
long the pump will actually run before it goes dry, but I suspect that
it is 6-24 hours.

The pump and prime pot are above the water line, so it is sucking water
up to the pump. At this point it would not be possible to position the
pump below water line.

After completely filling the prime pot and starting the pump, I have
noticed that the water level in the prime pot immediately drops to
approx. 3/4 full, which is slightly below the input of the prime pot.
Is this normal?

I imagine that it must be a small leak somewhere on the input side that
is allowing air to enter. Any ideas as to how to identify such a small
leak?

--Bob--

Phyllis and Jim wrote:
Could be...Loss of suction...air entry...insufficient flow rate in feed
pipe. Can you watch it get lower?

Is your pump a gravity-flooded prime or does it need to suck water up
to the pump. If it can draw from a flooded reservoir, it is less
likely to pull itself dry. To do that, the pump needs to be lower than
the pond level and has to have sufficient flow to keep drawing water
instead of air.

Jim


Bob wrote:
I recently installed an external pump with a priming pot for my pond.
After a few hours of running I discover that the pump is still running
but there is no water flow and the priming pot is empty of water. I
can stop the pump, refill the priming pot, restart it and it will pump
water for a few more hours until it runs out again. I am confident
that the power to the pump has not gone out temporarily. I have also
verified that I can remove power from the pump and restart it just
fine, since I have a swing valve on the input of the priming pot that
prevents it from emptying. Any ideas as to what could be causing this?

Hal wrote:
On 5 Sep 2006 09:03:30 -0700, "Bob" wrote:

I recently installed an external pump with a priming pot for my pond.
After a few hours of running I discover that the pump is still running
but there is no water flow and the priming pot is empty of water. I
can stop the pump, refill the priming pot, restart it and it will pump
water for a few more hours until it runs out again. I am confident
that the power to the pump has not gone out temporarily. I have also
verified that I can remove power from the pump and restart it just
fine, since I have a swing valve on the input of the priming pot that
prevents it from emptying. Any ideas as to what could be causing this?

Tube/hose/fitting/cracked housing leak above the waterline.

Regards,

Hal