We recently helped a customer who was concerned their SPP2 Puddle Pump had developed a fault. The pump would clear water well at first, but as the level dropped it appeared to stop working, and water seemed to flow back out towards the pump. They understandably assumed something had failed.
After reviewing the video they sent us, we could see the pump was doing exactly what we would expect it to do in those conditions. No fault, no warranty issue, just physics. Because this comes up fairly often, here is what is actually happening and what you can do about it.
What is going on?
Puddle pumps are designed to work in very shallow water, and that is exactly where this behaviour shows up. The sequence usually looks like this:
1. The pump starts and fills the discharge hose with water.
2. The water level drops to the last few millimetres.
3. With so little water left, the pump begins to draw in air.
4. Once air enters the pump, it can no longer hold the column of water sitting in the hose.
5. That water flows back down the hose, through the pump, and returns to the area you have just cleared.
From the outside, it looks like the pump has cut out or is running in reverse. In reality, the pump simply cannot keep hold of a full hose of water once it is pulling air instead of water. The longer the hose run, and the higher the water has to be lifted, the more water there is to come back.
The air release valve fitted to pumps like the SPP2 reduces the risk of airlocking, but it cannot stop backflow. No pump can keep drawing water once the remaining depth is below what it needs, and no open discharge line will hold its water column once air gets into the system.
The fix: a non-return valve
The answer in most cases is simple. A non-return valve fitted to the pump outlet acts as a one-way gate. Water passes freely on the way out, but the valve closes the moment flow stops or reverses. The water already pumped stays in the hose instead of draining back, so you keep the ground you have gained, and the pump re-primes faster when the level rises again.
This is not a workaround, more expensive low-level pumps, such as the Stream SPK530 and the Tsurumi LSC1.4S, have a non-return valve built into their design for exactly this reason. Fitting one to a pump like the SPP2 gives you the same protection.
For the SPP2 you need a 1 inch BSP non-return valve and a matching 25mm hose tail. Screw the valve onto the pump outlet, fit the hose tail to the valve, push on your 25mm discharge hose and secure it with a hose clip. Our exclusive Non-Return Valve and Hose Tail Kit includes both parts.
Keep your hose run sensible
A non-return valve deals with the backflow, but the installation still matters. Keep hose runs as short and direct as practical. Very long runs and high lifts increase friction losses, reduce flow, and increase the volume of water the valve has to hold. If your pump seems to be underperforming, the hose arrangement is often the first place to look. Our Pump Performance Calculator will show you how hose length and lift affect real-world flow.
A note on site-specific advice
We are always happy to advise on pump specifications: flow rates, head heights, outlet sizes, solids handling and which pump suits which type of water. What we cannot do from a phone call or a video is give site-specific advice, because we cannot see the full picture of hose length, pumping distance, vertical lift and discharge arrangement.
If you need that level of detail, our Engineering Review Service is the right route. An engineer reviews your complete installation and provides tailored recommendations. Unless we have carried out an engineering review, our advice is limited to pump specifications rather than your specific setup.
Conclusion
If your puddle pump clears water and then seems to let it flow back when the level gets very low, it is almost certainly not faulty. Fit a non-return valve to the outlet, keep the hose run short, and the problem should disappear.
