ᐅ Issues with Pump in Cistern / Rainwater Tank

Hello dear forum community,

I’ll try to explain my problem:

In the garden, I have a cistern with a capacity of about 2,000 liters (approx. 528 gallons) that collects rainwater (about 2.50 m deep (8.2 ft), and the emergency overflow is positioned so that the water level can only rise to about 50 cm (20 inches) below the top edge, i.e., around 2.0 m (6.6 ft) height).
I bought a standard garden pump to occasionally pump water out.
A hose about 5–6 m (16–20 ft) long is connected to the pump and reaches into the cistern. At the open end of the hose, there is a kind of check valve with a mesh screen that prevents water standing in the hose from flowing back into the cistern when the pump is off and also stops dirt from entering the pump. When the pump is running, it creates suction that opens the check valve and allows water to be drawn from the cistern.

This worked well several times, but now it no longer works. Apparently, the valve no longer opens properly. However, the valve should not be broken because a test with a rain barrel (same height as the pump) ran without problems for minutes. Without the valve, the water flows out of the hose so fast that a test is not possible.
I also can’t imagine that the pump (bought earlier this year) suddenly can’t handle the height. The pump’s delivery pressure was very good during the rain barrel test.

Does anyone have any ideas what I could test or do? Or do you need more detailed information?

Thanks for suggestions
Martin

Was the cistern full when it worked and is it now empty? Besides the pump’s delivery pressure, there is a maximum suction height. Submersible pumps are usually more suitable in this case. But thinking about it… with such a small height difference, it shouldn’t be an issue. The hose may need to be vented, meaning filled with water, before the pump can work again, because it can suck up water but won’t operate with air in the system. This is also something submersible pumps do not experience.

The cistern was full when we installed the pump, and we were able to irrigate perfectly for some time. Then, due to the dry period, the cistern slowly emptied, and the pump was left "idle." When the cistern was full again, we switched on the pump in good faith, but nothing happened...

I have already tried several things, but nothing has worked permanently:

- I filled the hose and the pump completely with water several times (and the pump was able to deliver this amount of water without any problems, but nothing beyond that).

- Since we live on a slope and the cistern (its upper edge) is located on the upper part of the hillside, I placed the pump a bit downhill (as far as the hose allowed). The idea was that the pump would be at or below the water level of the cistern. This worked well for a short time but stopped working again fairly quickly... although I can’t say for sure if the water level in the cistern (which visibly dropped during this short period) fell below the pump’s standing height.

The technical data of the pump are: 750 watts power, 7.5m (25 feet) suction height, 55 l/min (14.5 gallons per minute) flow rate, 4.7 bar (68 psi) delivery height.

PS: I have also considered a submersible pump—there was one recently at Lidl—but it said "Max. particle size 8mm (0.3 inches)," and since our water is quite turbid, I did not dare try it.

An 8mm particle size is quite large. Usually, a leaf strainer is installed in the gutter, and I have even seen tea strainers used, which filter down to about 1/2mm (0.02 inches) of particles passing through. Then the water can be passed through a second filter, and if the cistern is sealed properly, the water inside can reach drinking water quality, biologically purified by a slight sediment at the bottom.

Is the hose end actually submerged in the water? The pump seems to be working... Could a stone be blocking the hose end?

The end of the hose is at least one meter (3 feet) underwater. The only possible issue might be that the hose end is not positioned vertically in the water, if that makes any difference. I might need to try attaching something additional to weigh down the hose or filter...