Anti-siphon valve

for consistently quiet operation of the condensate pump

Prevents gurgling noises when the water outlet is positioned lower than the pump.

If the water outlet lies below the pump, a gurgling sound may occur after shutdown – a normal physical phenomenon.

The anti-siphon valve reliably prevents this: it is installed at the highest point of the discharge tube and automatically compensates pressure differences.
This keeps the pump quiet – both at standstill and when starting up again.

What is an anti-siphon valve?

An anti-siphon valve is a special valve fitted into the discharge tube of condensate pumps.
It reliably prevents gurgling noises that can occur when negative pressure builds up in the system after the pump stops running.

How does an anti-siphon valve work?

Water flows freely through the two main ports of the valve.
If a negative pressure occurs within the water stream, the side valve opens and lets air in.
When overpressure builds up, the valve remains closed.

This prevents the water column inside the discharge tube from drawing all remaining water out of the pump.
As a result, the pump stays silent when idle and restarts without delay or slurping noises.

When should an anti-siphon valve be used?

An anti-siphon valve is required when the outlet of the closed water system is positioned below the pump’s intake point.

If the outlet is located above the pump, installation is not necessary because no accelerating siphon effect occurs.
The valve should therefore only be used when the water outlet is lower than the pump.

What happens if an anti-siphon valve is missing or incorrectly installed?

In this case, a typical gurgling noise might occur after the pump stops – first increasing, then fading again.
It begins a few seconds after the pump shuts down and usually lasts for about 10–20 seconds, until the discharge tube is completely empty.
After that, the condensate pump is silent again.

Where should the anti-siphon valve be installed?

The ideal position is at the highest point of the discharge hose (point D) or slightly before or after it.

For higher discharge heights above 1 m, installation at point C is recommended, provided this point is significantly above opening B.
This prevents water from flowing back from the discharge tube into the pump reservoir.

The valve must be watertight when connected to the PVC tubes, mounted with the opening facing upwards, and remain easily accessible.

What are the alternatives to an anti-siphon valve?

An alternative option is to significantly increase the diameter of the downward line –
for example, by placing a corrugated hose over the PVC tube.

The PVC tube should be guided precisely to the pump’s intake port and cut to length there.
The corrugated hose should be pulled up as far as possible to ensure that, in case of blockage at the lower section, water cannot escape at the top.